University of Pretoria etd – Combrinck, M (2006) Development of an automated analysis of TDEM data for the delineation of a finite conductor in a conductive half space. by Magdalena Combrinck A thesis submitted in partial fulfillment of the requirements for the degree of Doctor in Philosophy in Exploration Geophysics In the Faculty of Natural and Agricultural Science of the University of Pretoria.
University of Pretoria etd – Combrinck, M (2006) Development of an automated analysis of TDEM data for the delineation of a finite conductor in a conductive half space. by Magdalena Combrinck Supervisor: Professor W. J.
University of Pretoria etd – Combrinck, M (2006) A remaining concern when implementing the S-layer transform is found in two consecutive numerical differentiations and various approaches are analysed to ensure stable differentiation procedures. The automated algorithm is applied to a variety of synthetic models to validate its accuracy and finally examples are shown of its application to both ground and airborne data sets.
University of Pretoria etd – Combrinck, M (2006) TABLE OF CONTENTS 1 INTRODUCTION......................................................................................................................1 1.1 General overview ...................................................................................................................1 1.2 Objective .................................................................................................................................
University of Pretoria etd – Combrinck, M (2006) 5 4.5.5 Imaged conductivity depth sections generated from synthetic data ...................93 APPLICATION TO FIELD DATA......................................................................................100 5.1 Introduction........................................................................................................................100 5.2 Ground survey..............................................................................................
University of Pretoria etd – Combrinck, M (2006) LIST OF FIGURES Figure 2-1 The use of equivalent current filament concept in understanding the behaviour of TEM fields over a conducting half space (after Nabighian and Macnae, 1991)................................................................................................................................8 Figure 2-2 Conductive sheet parameters.............................................................................................
University of Pretoria etd – Combrinck, M (2006) data, (c) equally spaced points without smoothing of data and (d) equally spaced points with smoothing. ..............................................................................................................46 Figure 4-6: A summary (in ascending order) of the average error over twenty data points for each of the alternatives in Figure 4.5. (ES: equal spacing, US: unequal spacing) .....47 Figure 4-7: Synthetic data and model for three-layer earth......
University of Pretoria etd – Combrinck, M (2006) Figure 4-27: Imaged conductivity versus depth for two layers of decreasing conductivity; first layer thickness 200m..................................................................................71 Figure 4-28: Cumulative conductance versus depth for two layers of increasing conductivity; first layer thickness 200m..................................................................................
University of Pretoria etd – Combrinck, M (2006) Figure 4-49: Cumulative conductance for a 2 S/m plate of 20 m thickness at 150 m depth in 0.02 S/m host rock. The horizontal dimensions vary from 100 m to infinite. ..........................................................................................................................................85 Figure 4-50: Imaged conductivity for a 2 S/m plate of 20 m thickness at 150 m depth in 0.02 S/m host rock.
University of Pretoria etd – Combrinck, M (2006) Figure 5-5: Line 4950, Station 400. Top: Raw data with calculated cumulative conductance and imaged conductivity. Middle: No filter effect on input data values, only on cumulative conductance curve with imaged conductivity of filtered conductance values. Bottom: Input data filtered for late channel erratic behaviour and filtered cumulative conductance values. ................................................... 106 Figure 5-6: Line 4950, Station 450.
University of Pretoria etd – Combrinck, M (2006) Figure 5-22: Conductivity depth section in greyscale with conductor decay constants plotted at scaled channel positions. ...................................................................................... 124 Figure 5-23: Conductivity depth section in greyscale with channels on stations showing sign changes indicated in blue................................................................................................
University of Pretoria etd – Combrinck, M (2006) ACKNOWLEDGMENTS The author wishes to thank Prof. Willem Botha (my supervisor) for his patience and when it was required, the lack thereof. Many other people including family, friends, training partners and colleagues contributed to this work through their continued moral support.
University of Pretoria etd – Combrinck, M (2006) Chapter 1 1 INTRODUCTION "I believe that we cannot live better than seeking to become still better than we are." (Socrates) 1.1 General overview The Time Domain Electromagnetic (TDEM) method, also referred to as Transient EM (TEM), has been used in mineral exploration since the late 1950’s. The basic theory of this method is defined in totality by four differential equations, known as Maxwell’s equations.
University of Pretoria etd – Combrinck, M (2006) forward modeling and is the reason why synthetic data is normally used as a first run to test new interpretation algorithms. The third factor proves to be the most difficult – accurately solving Maxwell’s equations. These equations can only be solved analytically for a few very simple geometrical models and only if assumptions regarding homogeneity, isotropy, frequency dependence, and frequency and conductivity ranges are made.
University of Pretoria etd – Combrinck, M (2006) One of the most common assumptions is that the host rock containing the ore body of interest is very resistive. This implies a significant decrease in computational effort, but unfortunately is one of the assumptions not always met in true field conditions.
University of Pretoria etd – Combrinck, M (2006) Chapter 2 2 OVERVIEW OF ELECTROMAGNETIC THEORY FOR GROUND, INLOOP TDEM DATA "There is a theory which states that if ever anybody discovers exactly what the Universe is for and why it is here, it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another theory which states that this has already happened.” (from “The Hitchhiker’s guide to the Galaxy”, Douglas Adams) 2.
University of Pretoria etd – Combrinck, M (2006) strategy allows for both 1D and 3D model considerations. The late time mathematical approximations are implemented for most procedures. 2.3 Analytical TDEM responses for four common models Analytical responses for TDEM data are calculated by solving Maxwell’s equations.
University of Pretoria etd – Combrinck, M (2006) In these equations the dielectric permittivity, magnetic permeability and electric conductivity should all be regarded as tensor functions of angular frequency, position, time, temperature, pressure and magnetic/electric field strength. However, in order to derive analytical solutions some assumptions regarding these parameters are necessary.
University of Pretoria etd – Combrinck, M (2006) • Thin, conductive sheet (S-layer) • Finite conductor in a resistive host rock (half space) • Finite conductor in a conductive host rock (half space). 2.3.1 TDEM central-loop response over a conductive half space The quasi-static approximation of EM-field propagation in a half space can be described as a diffusion process (Nabighian, 1979).
University of Pretoria etd – Combrinck, M (2006) Figure 2-1 The use of equivalent current filament concept in understanding the behaviour of TEM fields over a conducting half space (after Nabighian and Macnae, 1991). The quasi-stationary (derivative of) magnetic field transient response of a central-loop, step-current system over a conductive earth is given by Kaufman and Keller (1985) as ∂H z I =− ∂t µ 0σa 3 ( ) 2 ⎡ −u 2 ⎤ 2 ⎢⎣3erf (u ) − π 12 u 3 + 2u e ⎥⎦ (2.
University of Pretoria etd – Combrinck, M (2006) electromotive force (emf) is directly proportional to t −5 2 for an ideal step function excitation. This behaviour is described as a power-law decay with time and manifests as a straight line with a slope of m = –5/2 on a graph of log (emf) versus log (t). The horizontal component of the emf can be shown to exhibit the same behaviour (Kaufman and Keller, −3 1983); the only difference being that it shows a time-decay proportional to t in the late time.
University of Pretoria etd – Combrinck, M (2006) Transmitter loop Thin, conductive sheet with conductance S Siemens. t=t1 t=t2 t=t3 Figure 2-3 Equivalent current filaments (images) for a conducting thin sheet at various times after current interruption in the transmitter loop (after Nabighian and Macnae, 1991).
University of Pretoria etd – Combrinck, M (2006) of 2t + 2d >> r (where r now represents the small loop radius after reciprocity) and µ0 S simplifying equation 2.3 we have 3M 1 2 16 Sr (τ + d )4 emf late time emf late time ∂H z 3M 1 = = =− 2 ∂t effective Rx area 16 Sπ (τ + d )4 nr πr where M = magnetic dipole moment of the transmitter (large) loop emf late time = − τ= (2.4) (2.5) t µ0 S nr = number of turns in receiver loop r = radius of the small receiver loop[m].
University of Pretoria etd – Combrinck, M (2006) τ= σµa 2 π2 (2.6) σ = conductivity of sphere [S] a = radius of sphere [m], so that emf sphere late time = Ae −t τ (2.7) A = constant containing geometrical information. Emf measurements taken at this stage of “late time” will manifest as a straight line when plotted on a semi-log graph of ln(emf) versus time.
University of Pretoria etd – Combrinck, M (2006) the diffusion of the smoke-ring currents (Nabighian and Macnae, 1991) and the assumptions stated in 2.3 are not valid anymore. This different nature of the inducing field has two consequences. Firstly, the toroidal vortex (induced) currents will not be as strong as in the case of a conductor in free space, because of the reduced ∂B/∂t component (fields are varying slower with time).
University of Pretoria etd – Combrinck, M (2006) component (hz(t)) generated from a vertical magnetic dipole source through abrupt termination of current in a horizontal loop. The response for a sphere in free space (σ1/σ2=0) corresponds with solutions obtained by Nabighian (1971) and McNeill (1980). Figure 2-5 A permeable conducting sphere embedded in a conducting infinite space. The dipolar source is located at S(r0,0,0) outside the sphere (after Singh 1973).
University of Pretoria etd – Combrinck, M (2006) Figure 2-7 Time characteristic of hv1θr(t) for r/a=2, µ2/µ1=1, and variable σ1/σ2 (after Singh 1973). Figure 2-8 Time characteristic of hu1θθ(t) for r/a=2, µ2/µ1=1, and variable σ1/σ2 (after Singh 1973). The curves for hv1rr(t) reach a maximum at T>0 and then decay at a rate slower than the case σ1/σ2=0, whose maximum occurs at T =0.
University of Pretoria etd – Combrinck, M (2006) power law decays; straight lines with equal slopes, independent of the actual conductivity values. Figure 2.7 shows the hv1θr(t) component as a function of time, once again comparing free space with conducting space responses. The delayed and reduced peaks with straight-line behaviour in the late time are still present, but the most interesting feature is the sign change that occurs in this response when a conducting space is introduced.
University of Pretoria etd – Combrinck, M (2006) 2.4 Conclusion It is possible to describe electromagnetic field propagation analytically for only a few simplified earth models. Modelling realistic geological environments imply numerical solution of Maxwell’s equations which are very time-consuming and not yet commonly used in industry.
University of Pretoria etd – Combrinck, M (2006) Chapter 3 3 CONVENTIONAL INTERPRETATION TECHNIQUES "The definition of insanity is doing the same thing over and over and expecting different results.” (Benjamin Franklin, 1706-1790) 3.1 Introduction The ultimate goal of doing any geophysical survey is to deliver a map or model indicating the subsurface distribution of physical properties, i.e. conductivity in the case of TEM and to interpret this data in terms of geology.
University of Pretoria etd – Combrinck, M (2006) The second type of target is considered to be a half space or layered earth. The theoretical assumptions made in this case are that there are no finite conductors present and that the subsurface layers are perfectly horizontal. Mathematically this means that all processing reduces to one dimension. TEM surveys designed for this type of target emphasize vertical variations in conductivity and are called sounding surveys.
University of Pretoria etd – Combrinck, M (2006) modelling software still approximates complex geological units in terms of simplified geometries as well as mathematical simplifications sometimes needed to solve a problem (see 2.3). Since TEM is an active source method (as opposed to magnetics and gravity) the transmitter current waveform, geometry and position all determine the actual shape and amplitude of anomalies.
University of Pretoria etd – Combrinck, M (2006) 3.4 Limitations on automation of inversion techniques Forward modelling as defined in 3.3 cannot be automated as it includes the active involvement of a geophysicist at every guess of a new model. In fact, inversion is the process whereby “guessing of models” is taken over by an algorithm or computer.
University of Pretoria etd – Combrinck, M (2006) where mathematical solutions are found subject to geological truths such as dip, strike, conductivity ranges and limits on dimensions of bodies. However, this information is very rarely available in the exploration industry before TEM interpretations have to be done.
University of Pretoria etd – Combrinck, M (2006) inside the transmitter loop. It is impossible to see this behaviour in a conductive half space or layered earth environment and it therefore implies either an IP effect or extensive lateral variations (including two- or three-dimensional conductors) in the subsurface. Table 3-1 Summary of late time approximations and behaviour for four general models. Late time behaviour 1.
University of Pretoria etd – Combrinck, M (2006) 3.6 Transforms (Depth imaging) Spies and Frischknecht (1991) describe depth imaging techniques as low cost (i.e. fast and automated) alternatives to modelling and inversion to provide an approximate image of the resistivity section directly from observed data. Originally developed as a “processing” step they now appear very useful for interpretation.
University of Pretoria etd – Combrinck, M (2006) system data and only results applied to synthetic data are available in literature (GEOTEM (APPARENT) CONDUCTIVITY is a registered trademark of Geoterrex).
University of Pretoria etd – Combrinck, M (2006) Figure 3-2 Cross-section of the model (top); Conductivity-depth image obtained by differential S-transformation (centre); Conductivity-depth image obtained by regularized S-inversion (bottom). (After Tartaras et. al.
University of Pretoria etd – Combrinck, M (2006) 3.7 Combining Strategies Interpreting geophysical data almost never comprises the straightforward application of a fixed procedure. As with putting together the different pieces of a puzzle, the more information you have and the more angles you can view it from, the better your chances are of success. TEM data and processing are no different.
University of Pretoria etd – Combrinck, M (2006) Chapter 4 4 AUTOMATED INTEGRATED ANALYSIS OF TDEM DATA “Nature is not a competition. It doesn’t really matter, when you go out, if you don’t identify anything. What matters is the feeling in the heart.” (Richard Adams, B. 1920, British Writer) "Exploring the unknown defines the essence of humanity." (The author) 4.
University of Pretoria etd – Combrinck, M (2006) late time values often being more significant) and the fact that the half space (or background) response often dominates that of the target. A very simple approach was followed to minimize the effects of these two factors. Data at every station are presented as a fraction of an average response calculated over the complete data set.
University of Pretoria etd – Combrinck, M (2006) Figure 4-1 In (a) the raw data are presented in a contoured log-scale. In (b) the data were normalised using the half space value used in the forward model. In (c) the data were normalised as discussed above. 4.3 Decay curve analysis The decay curve analysis is implemented in three steps. • Decay curves analyzed for layered earth (i.e. power law) behaviour. • Decay curves analyzed for exponential decay indicating confined conductors.
University of Pretoria etd – Combrinck, M (2006) 4.3.1 Layered earth behaviour The objectives of this analysis are: • to determine whether there is any straight line behaviour in the logarithmic domain of a sounding data set; • to determine the largest number of channels (and channel numbers) on which the behaviour can be found; • to test whether these slopes are close to either -2.5 or -4 and consequently • to classify the sounding as half space or S-layer type.
University of Pretoria etd – Combrinck, M (2006) Repeat for NumberOfChannels=4 to NumberOfChannels=(20-4) Repeat for beginChannel=0 to beginChannel=(20-NumberOfChannels) Calculate least squares regression parameters: m := slope c := y-intercept R := correlation coefficient 2 Calculate closest distance of m to either -2.5 or -4 mError = minimum of abs(m+2.5) AND abs(m+4.0) Test whether calculated parameters fall within user-specified (or default) limits.
University of Pretoria etd – Combrinck, M (2006) slope values that need to be tested for and any regression fit within the specified R2 limit is accepted as a possible conductor. The channels exhibiting the exponential decay are stored as well as the decay constant which is calculated as the inverse of the “best fit” slope. 4.3.
University of Pretoria etd – Combrinck, M (2006) • Speed • No need for an initial model • Although it is based on the same imaging principles as the CDI transform it is easier to implement with fewer empirical factors that need to be included • The late time approximation used in the algorithm is very applicable to the impulse response, central-loop configuration this work is based on • For the specific case of a conductive host rock environment the S-layer differential transform shows good resolv
University of Pretoria etd – Combrinck, M (2006) where S = cumulative conductance [S] d = depth [m] M = magnetic dipole moment of transmitter [Am 2 ] 2 ∑ = receiver area [m ] n = number of turns of receiver coil t = time [s] ⎛ ∂B ⎞ V = electromotive force of ideal receiver loop [V] = − ∑ n⎜⎜ z ⎟⎟ ∂t ⎝ ⎠ ′ V = time derivative of measured voltage V [V/s]. The time derivative of the measured voltage (|V|’) is the parameter that has to be determined through numerical differentiation.
University of Pretoria etd – Combrinck, M (2006) 4.4.2 Numerical differentiation of TEM data In the late time, TDEM responses measured over a one-dimensional subsurface can be described as a power-law function, equation 4.4, with k=2.5 for a half space and k=4 for a thin conductive layer (S-layer). This creates the possibilities of using standard polynomial approximations, but in the logarithmic and semi logarithmic domains. Consider the following power-law decay: V (t ) = At − k A = constant ( 4 .
University of Pretoria etd – Combrinck, M (2006) apply polynomial-based differentiation techniques to data in the domain where they can be approximated best by polynomial functions. These very specific properties of being logarithmically sampled and exhibiting power-law or exponential decays make TEM data distinctly unsuitable for the most common numerical differentiation schemes such as the Lagrange formulas (Burden and Faires, 1993) which are based on functions exhibiting polynomial behaviour. 4.4.2.
University of Pretoria etd – Combrinck, M (2006) The formulas for transforming the derivatives are straightforward, trivial to apply, and analytically correct (i.e. no truncation error is induced in the transformation process). This enables us to choose the best domain for performing numerical differentiation based on the nature of data and available differentiation schemes. Synthetic TEM data for a 10 ohm.m half space are used to illustrate this point.
University of Pretoria etd – Combrinck, M (2006) enough to reconstruct with confidence and an exact comparison of this method with the other methods is not included in this study. Tartaras et. al. (2000) also applied smoothing of data “… prior to and following differentiation”. This is a common technique applied to reduce noise but ultimately alters data.
University of Pretoria etd – Combrinck, M (2006) enhanced in derivative calculations), computer round-off effects and how accurately the causative function can be approximated locally by a second order polynomial. 4.4.2.2.2 Derivative of cubic spline interpolated function (referred to as “cubic spline derivative method”) The Lagrange three-point method will give analytically correct results for functions of order one or two.
University of Pretoria etd – Combrinck, M (2006) However, low order polynomials will result in loss of high frequency information and high degree polynomials still suffer from unwanted oscillations. TEM is based on diffusion of electrical currents into the earth and this is a smooth process, never oscillating in nature, and therefore not suited to this type of interpolation.
University of Pretoria etd – Combrinck, M (2006) For the case where A is singular, not square or a non-linear operator, equation 4.12 must be solved with a method such as generalised least squares inversion or other equivalent techniques (Cooper, 2004).
University of Pretoria etd – Combrinck, M (2006) where c can take on any value (implying an infinite number of solutions). An easy solution is to use definite integrals instead, so that b ∫ f ′( x)dx = f (b) − f (a). (4.15) a From equation 4.12, the system of equations that has to be solved now reduces to a general form as shown in equation 4.16. ⎡ a11 a12 ⎢a . ⎢ 21 ⎢ . . ⎢ . . ⎢ ⎢a . ⎣ n1 . . a1n ⎤ ⎡ f ′( x1) ⎤ ⎡ f ( xb ) − f ( xa ) ⎤ ⎥ . . . ⎥⎥ ⎢⎢ . ⎥⎥ ⎢⎢ . ⎥ ⎥. . . . ⎥⎢ . ⎥ = ⎢ . ⎥⎢ ⎥ ⎢ ⎥ . . .
University of Pretoria etd – Combrinck, M (2006) ⎡5 ⎢ 4 ⎢1 ⎢0 h⎢ ⎢0 3⎢ ⎢0 ⎢0 ⎢ ⎢⎣ 0 2 −1 4 1 4 f ( x2 ) − f ( x1) ⎤ 0 ⎤ ⎡ f ′( x1) ⎤ ⎡ ⎥⎢ ⎥ ⎢ ⎥ ′ ( ) ( ) − f x f x ( ) f x . . 0 ⎥⎢ ⎥ 3 1 2 ⎥ ⎢ ⎥ ⎢ f ( x4 ) − f ( x2 ) ⎥ . 0 . 0 ⎥⎢ ⎥⎢ ⎥ ⎢ ⎥ ... . 1 . 0 ⎥⎢ ⎥=⎢ ⎥ ⎥ ⎥ ⎢ f (x ⎥ ) ( ) − f x . . . 0 ⎥⎢ n −1 n−3 ⎥ ⎢ ⎥ ⎢ 1 4 1 ⎥ ⎢ f ′( xn − 1)⎥ ⎢ f ( xn ) − f ( xn − 2 ) ⎥ ⎥⎢ ⎥ ⎢ ⎥ −1 2 5 ⎥ ⎣ f ′( xn ) ⎦ ⎣ f ( xn ) − f ( xn − 1) ⎦ 4 4⎦ 0 . 0 1 4 1 0 1 4 . . . . . 0 . . 0 .
University of Pretoria etd – Combrinck, M (2006) data to equal intervals is that the weights (and inverse matrices) used for differentiation and smoothing only has to be calculated once. Applying the transform to unequally spaced data points means less tampering with the original data but it is much more time intensive. The method use for smoothing is the three-point moving average filter for equally spaced points and a weighted extension for unequally spaced points (equation 4.22).
University of Pretoria etd – Combrinck, M (2006) The inversion method gives the smallest average error, followed by the cubic spline and three point methods. For unsmoothed data the equally spaced points slightly outperform the unequally spaced points, but the reverse is true for smoothed data. Smoothing of data seems to be the largest contributing factor to errors in noise-free data.
University of Pretoria etd – Combrinck, M (2006) 3.5 Lagrange Three Point 3 Average percentage error Cubic Spline 2.5 Inverse of Integration 2 1.5 1 0.5 ES, smoothed US, smoothed ES, smoothed US, smoothed ES, smoothed US, smoothed US ES US ES US ES 0 Figure 4-6: A summary (in ascending order) of the average error over twenty data points for each of the alternatives in Figure 4.5. (ES: equal spacing, US: unequal spacing) 4.4.3.
University of Pretoria etd – Combrinck, M (2006) The numerical calculation of the S-layer transform was done using the following steps: ⎛ ∂B ⎞ 1. Input |V| values ⎜ = z if normalised to receiver area of 1m 2 ⎟ ⎝ ∂t ⎠ 2. Calculate |V|’, i.e. ∂ 2 Bz ∂t 2 3. Calculate S from equation 4.1 4. Calculate d from equation 4.2 5. Calculate ∂S =σ ∂d Numerical differentiations are performed in steps 2 and 5.
University of Pretoria etd – Combrinck, M (2006) 0.14 Smoothed dB/dt Smoothed dB/dt and S Imaged Conductivity [S/m] 0.12 Smoothed dB/dt, S and dS/dd 0.1 0.08 0.06 0.04 0.02 0 0 100 200 300 400 500 600 700 800 600 700 800 Depth [m] 0.6 Imaged Conductivity [S/m] 0.4 0.2 0 -0.2 Smoothed dB/dt -0.4 Smoothed dB/dt and S Smoothed dB/dt, S and dS/dd -0.6 Smoothed dB/dt, d(dB/dt)/dt, S and dS/dd -0.
University of Pretoria etd – Combrinck, M (2006) (b) 0.25 Lagrange Three-Point Cubic Spline Inverse of Integration 0.2 Imaged Conductivity [S/m] Imaged Conductivity [S/m] (a) 0.25 0.15 0.1 0.05 0 -0.05 0.2 0.15 0.1 0.05 0 -0.05 400 Depth [m] 600 800 (c) 0.25 (d) 0.25 Imaged Conductivity [S/m] 200 Imaged Conductivity [S/m] 0 0.2 0.15 0.1 0.05 0 -0.05 0 200 0 200 400 Depth [m] 600 800 600 800 0.2 0.15 0.1 0.05 0 -0.
University of Pretoria etd – Combrinck, M (2006) 1.E-05 Sounding 1 Sounding 2 Sounding 3 Sounding 4 ABS(dB/dt) [T/s] 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 1.E-12 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 Time [s] Figure 4-10: Four field data soundings; 1 to 4 are very smooth and considered to be clean data, while 5 & 6 contains noise. Lagrange Three-Point Cubic Spline Inverse of Integration 1.E-01 1.E-02 (b) 1.E+00 Imaged Conductivity [S/m] Imaged Conductivity [S/m] (a) 1.E+00 1.E-03 1.
University of Pretoria etd – Combrinck, M (2006) Sounding 1 (Figure 4-11) would be considered “noise-free” in that none of the data points would probably be masked (ignored) in manual interpretation of the data. However, comparing the smoothed and unsmoothed results it is clear that it does contain some noise which can be filtered out successfully with the weighted moving average filter.
University of Pretoria etd – Combrinck, M (2006) function, implying more than one S value for each depth and this is not accounted for in re-sampling with the cubic spline method.) (b) 1.E+02 Imaged Conductivity [S/m] Imaged Conductivity [S/m] (a) 1.E+02 1.E+01 1.E+00 1.E-01 1.E-02 Lagrange Three-Point Cubic Spline Inverse of Integration 1.E-03 0 100 200 1.E+01 1.E+00 1.E-01 1.E-02 1.E-03 300 0 100 200 Depth [m] 300 0 100 300 (c) 1.E+02 (d) 1.
University of Pretoria etd – Combrinck, M (2006) Lagrange Three-Point Cubic Spline Inverse of Integration (b) 1.E+00 Imaged Conductivity [S/m] Imaged Conductivity [S/m] (a) 1.E+00 1.E-01 1.E-02 1.E-03 1.E-01 1.E-02 1.E-03 200 Depth [m] 300 400 (c) 1.E+00 (d) 1.E+00 Imaged Conductivity [S/m] 100 Imaged Conductivity [S/m] 0 1.E-01 1.E-02 1.E-03 0 100 200 300 400 0 100 200 Depth [m] 300 400 0 100 200 Depth [m] 300 400 1.E-01 1.E-02 1.
University of Pretoria etd – Combrinck, M (2006) S-layer transform remains very fast (less than five seconds on a PC for 1500 soundings) no matter which differentiation method is chosen. Finally, only good quality data can be expected to give good quality results and if a truly automated process is required a filter passing only relatively noise-free data should be applied before the S-layer differential transform is applied . 4.5 4.5.
University of Pretoria etd – Combrinck, M (2006) 1.E+05 10 Ohm.m WJ Botha Late Time 50 Ohm.m 1.E+04 Resistivity [Ohm.m] WJ Botha Late Time 100 Ohm.m 1.E+03 WJ Botha Late Time 500 Ohm.m WJ Botha 1.E+02 Late Time 1000 Ohm.m WJ Botha Late Time 1.E+01 5000 Ohm.m WJ Botha Late Time 1.E+00 1.E-05 1.E-04 Time [s] 1.E-03 1.E-02 1.E-01 Figure 4-15: Half space resistivities compared to resistivities from S-Layer differential transform. The 10 ohm.
University of Pretoria etd – Combrinck, M (2006) ⎛ ∂S ⎞ ⎛ ∂S ⎞ = ⎜ ⎟ / 2.6192 ⎜ ⎟ ⎝ ∂d ⎠ SCALED ⎝ ∂d ⎠ ⎞ ⎛ ⎟ ⎜ ⎜ ∂ ( S ⋅ S factor ) ⎟ =⎜ ⎟ d ⎜ ∂ (d ⋅ factor ) ⎟ ⎜ S factor ⎟⎠ ⎝ So that, 2.6192 = S factor ⎛ d factor ⎜ ⎜S ⎝ factor S 2 factor = d factor ⎞ ⎟ ⎟ ⎠ There are of course an infinite number of correction factors that will satisfy this requirement (Figure 4.16) and an urgent need arouse to explain the origin of this discrepancy.
University of Pretoria etd – Combrinck, M (2006) 3 Correction factor value [dimensionless] S_factor d_factor effective depth correction 2.5 2 3 1 2 1.5 1 0.5 0 1 51 101 151 201 251 301 Number Figure 4-16: Values for S and d corrections giving correct resistivity values and the effective depth correction resulting from each pair. (from Excel: summary of depth conversion factor models) 4.5.1.
University of Pretoria etd – Combrinck, M (2006) d FACTOR = 1 = 0.3818 2.6192 S FATOR = 1 this leads to a depth correction multiplication factor of 0.3818. 4.5.1.3 Correction factor: Possibility 3 The third possibility is that the equations used in the transform are indeed mathematically sound but that the physical assumptions regarding current distributions made in the S-layer transform lead to poor approximations of the models used. In figure 2.
University of Pretoria etd – Combrinck, M (2006) 35 Equivalent Current Filament 30 Electric Field Maxima Conductance [S] 25 20 y = 0.0333x + 5E-15 15 10 5 0 0 100 200 300 400 500 600 700 800 900 1000 Depth [m] Figure 4-17: Cumulative conductance curves for late time halfsapce approximations. Looking specifically at depths, the equivalent current filament depths range from 99 m to 920 m, while the electric field maxima map between 63 m and 577 m.
University of Pretoria etd – Combrinck, M (2006) 35 Equivalent Current Filament Electric Field Maxima Cumulative conductance S-Layer Corrected S layer Linear (Cumulative conductance S-Layer) Conductance [S] 30 25 20 y = 0.0127x - 5E-07 15 10 5 0 0 200 400 600 800 1000 1200 Depth [m] Figure 4-18: Cumulative conductance curves for late time half space and S-layer approximations.
University of Pretoria etd – Combrinck, M (2006) Ch. 1-5 Ch. 6-10 Ch. 11-15 Ch. 16-20 8.8E-05 0.000251 0.000799 0.002648 0.000107 0.000314 0.001014 0.003373 0.000131 0.000396 0.001287 0.004297 0.000162 0.000499 0.001636 0.005475 0.000201 0.000631 0.002081 0.
University of Pretoria etd – Combrinck, M (2006) MODEL 1: Two-layer earth Layer Thickness Resistivity (conductivity) 1 100 m 50 ohm.m (0.02 S/m) 2 infinite 5 ohm.m (0.2 S/m) Apparent conductivity [S/m] 10 Input model SLDT: no depth factor SLDT: depth factor 1 SLDT: depth factor 2 SLDT: depth factor 3 TEMIX 2L inversion TEMIX 10L smooth inversion 1 0.1 0.
University of Pretoria etd – Combrinck, M (2006) Apparent conductivity [S/m] 1 Input model SLDT: no depth factor SLDT: depth factor 1 SLDT: depth factor 2 SLDT: depth factor 3 TEMIX 3L inversion TEMIX 10L smooth inversion 0.1 0.01 0.001 0 50 100 150 200 250 300 350 400 450 500 Depth [m] Figure 4-20: Comparison of S-layer differential transform (SLDT) solutions using different depth factors and layered earth inversions of synthetic data for a three layer earth (thin conductive layer).
University of Pretoria etd – Combrinck, M (2006) Apparent conductivity [S/m] 0.5 0 -0.5 -1 Input model SLDT: no depth factor SLDT: depth factor 1 SLDT: depth factor 2 SLDT: depth factor 3 TEMIX 3L inversion TEMIX 10L smooth inversion -1.5 -2 -2.5 0 50 100 150 200 250 300 350 400 450 500 Depth [m] Apparent conductivity [S/m] 1 Input model SLDT: no depth factor SLDT: depth factor 1 SLDT: depth factor 2 SLDT: depth factor 3 TEMIX 3L inversion TEMIX 10L smooth inversion 0.1 0.01 0.
University of Pretoria etd – Combrinck, M (2006) in cumulative conductance with time can be mapped again (Figure 4-2 bottom). This behaviour is investigated in more detail in the next section. MODEL 4: Conductive plate in half space Half space resistivity (conductivity) 50 ohm.m (0.02 S/m) Plate resistivity (conductivity) 5 ohm.m (0.
University of Pretoria etd – Combrinck, M (2006) model than the three layer inversion. This is to be expected as the basic assumption of an infinite layer (in horizontal extent) is violated. MODEL 5: Conductive prism in half space Half space resistivity (conductivity) 50 ohm.m (0.02 S/m) Prism resistivity (conductivity) 5 ohm.m (0.
University of Pretoria etd – Combrinck, M (2006) In conclusion, the third scenario for correction correlates best with the actual model depths on synthetic data and was implemented in the software. 4.5.3 Behaviour of the S-layer transform when applied to synthetic data In order to test (and develop a better understanding of the method) the conductivity-depth results of the improved S-layer transform a number of synthetic models are presented with their corresponding transformed results.
University of Pretoria etd – Combrinck, M (2006) Cumulative Conductance [S] 100 10 1 0 100 200 300 400 500 600 700 Depth [m] Figure 4-24 Cumulative conductance versus depth, 0.02 S/m (50 Ω.m) half space . Imaged conductivity [S/m] 0.1 0.01 0 100 200 300 400 500 Depth [m] Figure 4-25 Conductivity versus depth, 0.02 S/m (50 Ω.m) half space.
University of Pretoria etd – Combrinck, M (2006) Two layer earth with decreasing conductivity (σ1>σ2) 4.5.3.2 Two models with different contrasts are presented in Figures 4-26 and 4-27. The first layer has a conductivity of 0.02 S/m and is 200 m thick in each instance while the second layer conductivity is changed from 0.002 S/m to 0.0002 S/m.
University of Pretoria etd – Combrinck, M (2006) Imaged Conductivity [S/m] 0.1 0.01 0.001 Two Layers: Layer 1, 0.02 S/m, 200 m; Layer 2, 0.002 S/m Two Layers: Layer 1, 0.02 S/m, 200 m; Layer 2, 0.0002 S/m 0.0001 0 100 200 300 400 500 600 700 800 900 1000 Depth [m] Figure 4-27: Imaged conductivity versus depth for two layers of decreasing conductivity; first layer thickness 200m. 4.5.3.
University of Pretoria etd – Combrinck, M (2006) assumption made in this method that cumulative conductance will always increase with increasing depth and the standard algorithm only calculates the derivatives for points until the depths start decreasing. For this specific case the slope of the curve was calculated in an alternate manner to investigate the conductivity behaviour.
University of Pretoria etd – Combrinck, M (2006) 100 Two Layers: Layer 1, 0.02 S/m, 200 m; Layer 2, 0.2 S/m Two Layers: Layer 1, 0.02 S/m, 200 m; Layer 2, 2 S/m 10 Imaged Conductivity [S/m] Two Layers: Layer 1, 50 Ohm.m, 200 m; Layer 2, 0.5 Ohm.m (Alternative dS/dd calculation): dashed lines negative 1 0.1 0.01 0.001 0 50 100 150 200 250 300 350 Depth [m] Figure 4-29: Imaged conductivity versus depth for two layers of increasing conductivity; first layer thickness 200m. 0.6 0.
University of Pretoria etd – Combrinck, M (2006) The physical implication of this phenomenon can possibly be explained by a reflection of the equivalent S-layer filament at the very conductive high contrast boundary. As currents are induced into the second layer it can act as a secondary source and induce currents in the first layer again, diffusing away from this source, i.e. upwards.
University of Pretoria etd – Combrinck, M (2006) 1 Imaged Conductivity [S/m] 0.04 S/m 0.2 S/m 2 S/m 10 S/m 0.1 0.01 0.001 0.0001 0 100 200 300 400 500 600 Depth [m] Figure 4-32: Imaged conductivity versus depth for a 15m thick layer of varying conductivity at 150m depth in a 0.02 S/m half space. 0.1 0.045 0.04 S/m 0.2 S/m 2 S/m 10 S/m 0.08 0.04 0.035 0.07 0.03 0.06 0.025 0.05 0.02 0.04 0.015 0.03 0.01 0.02 0.005 0.
University of Pretoria etd – Combrinck, M (2006) contrast cases are predicted accurately although the high contrasts are not accurately mapped. The two most conductive layers generate underestimated values for conductivity (Figures 4-32 and 4-33) and might be interpreted to be more resistive than the half space if the conductivity sections are consulted without reference to the distinctive cumulative conductance signature.
University of Pretoria etd – Combrinck, M (2006) Imaged Comductivity [S/m] 10 5m 10m 15m 20m 50m 100m 1 0.1 0.01 0 100 200 300 400 500 600 Depth [m] Figure 4-35: Imaged conductivity for a 0.2 S/m layer of varying thickness at 150m depth in a 0.02 S/m half space. 1.4 0.16 5m 10m 15m 20m 50m 100m 0.12 1.2 1 0.1 0.8 0.08 0.6 0.06 0.4 0.04 Imaged Conductivity [S/m] (50m,100m) Imaged Conductivity [S/m] 0.14 0.2 0.
University of Pretoria etd – Combrinck, M (2006) The effect of layer thickness for the high contrast scenario is presented in figures 4-37 – 439. Cumulative Conductance [S] 100 2m 5m 10m 15m 20m 10 1 0 100 200 300 400 500 600 Depth [m] Figure 4-37: Cumulative conductance for a 2 S/m layer of varying thickness at 150m depth in a 0.02 S/m half space. Imaged Conductivity [S/m] 1 2m 5m 10m 15m 20m 0.1 0.01 0.
University of Pretoria etd – Combrinck, M (2006) 0.2 Imaged Conductivity [S/m] 0.18 0.16 0.05 0.14 0.04 0.12 0.1 0.03 0.08 0.02 0.06 0.04 0.01 0.02 0 Imaged Conductivity [S/m] (20m) 0.06 2m 5m 10m 15m 20m 0 0 100 200 300 400 500 Depth [m] Figure 4-39: Imaged conductivity for a 2 S/m layer of varying thickness at 150m depth in a 0.02 S/m half space – linear scale. Except for the 2 m layer, all the curves exhibit the high contrast behaviour.
University of Pretoria etd – Combrinck, M (2006) Cumulative Conductance [S] 100 50m 150m 200m 250m 300m 10 1 0 100 200 300 400 500 600 Depth [m] Figure 4-40: Cumulative conductance for a 0.2 S/m layer of 20 m thickness at various depths in a 0.02 S/m half space. Imaged Conductivity [S/m] 1 50m 150m 200m 250m 300m 0.1 0.01 0 50 100 150 200 250 300 350 400 450 500 Depth [m] Figure 4-41: Imaged conductivity for a 0.2 S/m layer of 20 m thickness at various depths in a 0.
University of Pretoria etd – Combrinck, M (2006) 0.2 50m 150m 200m 250m 300m Imaged Conductivity [S/m] 0.18 0.16 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0 50 100 150 200 250 300 350 400 450 500 Depth [m] Figure 4-42: Imaged conductivity for a 0.2 S/m layer of 20 m thickness at various depths in a 0.02 S/m half space – linear scale. The last factor contributing to the thin layer anomaly investigated is the host rock conductivity. A 20 m thick plate having conductivity of 0.
University of Pretoria etd – Combrinck, M (2006) Cumulative Conductance [S] 100 10 0.1 S/m 0.04 S/m 0.02 S/m 0.01 S/m 0.0067 S/m 0.005 S/m 0.0002 S/m 1 0 100 200 300 400 500 600 Depth [m] Figure 4-43: Cumulative conductance for a 0.2 S/m layer of 20 m thickness at 150 m depth in various host rock conductivities. Imaged Conductivity [S/m] 1 0.1 S/m 0.04 S/m 0.02 S/m 0.01 S/m 0.0067 S/m 0.005 S/m 0.0002 S/m 0.1 0.01 0.
University of Pretoria etd – Combrinck, M (2006) 0.25 0.1 S/m 0.04 S/m 0.02 S/m 0.01 S/m 0.0067 S/m 0.005 S/m 0.0002 S/m Imaged Conductivity [S/m] 0.2 0.15 0.1 0.05 0 0 100 200 300 400 500 600 700 800 900 Depth [m] Figure 4-45: Imaged conductivity for a 0.2 S/m layer of 20 m thickness at 150 m depth in various host rock conductivities - linear scale.
University of Pretoria etd – Combrinck, M (2006) Cumulative Conductance [S] 100 10 100 m X 100 m 200 m X 200 m 300 m X 300 m 400 m X 400 m Infinite Sheet 1 0 100 200 300 400 500 600 Depth [m] Figure 4-46: Cumulative conductance for a 0.2 S/m plate of 20 m thickness at 150 m depth in 0.02 S/m host rock. The horizontal dimensions vary from 100 m to infinite. Imaged Conductivity [S/m] 1 100 m X 100 m 200 m X 200 m 300 m X 300 m 400 m X 400 m Infinite Sheet 0.1 0.01 0.
University of Pretoria etd – Combrinck, M (2006) 0.16 100 m X 100 m 200 m X 200 m 300 m X 300 m 400 m X 400 m Infinite Sheet Imaged Conductivity [S/m] 0.14 0.12 0.1 0.08 0.06 0.04 0.02 0 0 100 200 300 400 500 600 Depth [m] Figure 4-48: Imaged conductivity for a 0.2 S/m plate of 20 m thickness at 150 m depth in 0.02 S/m host rock. The horizontal dimensions vary from 100 m to infinite; linear scale.
University of Pretoria etd – Combrinck, M (2006) Imaged Conductivity [S/m] 1 100 m X 100 m 200 m X 200 m 300 m X 300 m 400 m X 400 m Infinite Sheet 0.1 0.01 0.001 0.0001 0 100 200 300 400 500 600 Depth [m] Figure 4-50: Imaged conductivity for a 2 S/m plate of 20 m thickness at 150 m depth in 0.02 S/m host rock. The horizontal dimensions vary from 100 m to infinite. 0.4 100 m X 100 m 200 m X 200 m 300 m X 300 m 400 m X 400 m Infinite Sheet Imaged Conductivity [S/m] 0.35 0.3 0.25 0.2 0.15 0.
University of Pretoria etd – Combrinck, M (2006) The plates show very similar responses compared to that of the infinite layer. The main differences are that the depths would be underestimated slightly for the smaller plates if the same criteria are used as for the infinite layer and that the finite plates cause “lower than background” imaged conductivity anomalies after the peak values, reaching negative values in the high contrast cases.
University of Pretoria etd – Combrinck, M (2006) 1 Imaged Conductivity [S/m] 100 m X 100 m X 100 m 200 m X 200 m X 200 m 300 m X 300 m X 300 m 400 m X 400 m X 400 m 0.1 0.01 0.001 0 100 200 300 400 500 600 Depth [m] Figure 4-53: Imaged conductivity for a 0.2 S/m prism at 150 m depth in a 0.02 S/m host rock. The prism dimensions vary from 100 m to 400 m. 0.3 100 m X 100 m X 100 m Imaged Conductivity [S/m] 0.25 200 m X 200 m X 200 m 300 m X 300 m X 300 m 400 m X 400 m X 400 m 0.2 0.15 0.
University of Pretoria etd – Combrinck, M (2006) 1 Imaged Conductivity [S/m] 300 m Prism 300 m Plate Infinite Sheet 0.1 0.01 0.001 0 100 200 300 400 500 600 Depth [m] Figure 4-55: Comparison between imaged conductivities of a 0.2 S/m prism, 20 m thick plate and infinite sheet of 20 m thickness at 150 m depth in a 0.02 S/m host rock. Both the plate and prism have horizontal dimensions of 300 m. Figure 4-55 shows a comparison of the infinite sheet, thin plate and prism responses.
University of Pretoria etd – Combrinck, M (2006) Cumulative Conductance [S] 100 10 100 m X 100 m X 100 m 200 m X 200 m X 200 m 300 m X 300 m X 300 m 400 m X 400 m X 400 m 1 0 100 200 300 400 500 600 Depth [m] Figure 4-56: Cumulative conductance for 2 S/m prisms at 150 m depth in a 0.02 S/m host rock. The prism dimensions vary from 100 m to 400 m. Imaged Conductivity [S/m] 1 0.1 0.01 100 m X 100 m X 100 m 0.001 200 m X 200 m X 200 m 400 m X 400 m X 400 m 300 m X 300 m X 300 m 0.
University of Pretoria etd – Combrinck, M (2006) 0.4 Imaged Conductivity [S/m] 0.35 0.3 0.25 0.2 0.15 0.1 100 m X 100 m X 100 m 0.05 400 m X 400 m X 400 m 200 m X 200 m X 200 m 300 m X 300 m X 300 m 0 0 100 200 300 400 500 600 Depth [m] Figure 4-58: Imaged conductivity for 2 S/m prisms at 150 m depth in a 0.02 S/m host rock. The prism dimensions vary from 100 m to 400 m; linear scale. 0.4 200 m X 200 m X 200 m Imaged Conductivity [S/m] 0.35 300 m X 300 m X 300 m 0.
University of Pretoria etd – Combrinck, M (2006) 4.5.4 S-layer differential transform compatibility filter The “returning smoke ring” behaviour illustrated in high conductivity contrast scenarios in 1.3 can also be observed in field data (Figure 4-60). 8 Cumulative conductance [S] 7 6 5 4 3 2 1 0 0 500 1000 1500 2000 2500 3000 3500 4000 Depth [m] Figure 4-60: Examples of field data showing "returning smoke ring” behaviour (stations -1200 and -150 from line 4950, Rosh Pinah data set).
University of Pretoria etd – Combrinck, M (2006) Step 2: Find the first following data point not conforming to S-layer late time behaviour. Apply the same conditions as in step 1, but look for the first point NOT satisfying these. The last point passed through the filter is then (d[i], S[i]). The value of “1” chosen in conditions (b) and (c) is chosen based on empirical analysis of the case history 1 data set consisting of 1500 soundings over both resistive and conductive terrain.
University of Pretoria etd – Combrinck, M (2006) Figure 4-61: S-layer differential transform results (conductivity depth section) on synthetic data. Top: Thin vertical plate (400mX 400m X 20m) Middle: Thin horizontal plate (400m X 400m X 20m) Bottom: Prism (400m X 400m X 400m). Left hand side are low contrast scenarios (0.2 S.m-1 conductor in 0.02 S.m-1 half space). Right hand side are high contrast scenarios (2 S.m-1 conductor in 0.02 S.m-1 half space).
University of Pretoria etd – Combrinck, M (2006) Channels are scaled so that channel 1 corresponds with the top of the section and channel 20 to the bottom. Note the half space (-2.5) decay that is observed on all models at some stage. Although conductors are present the conductive nature of the half space itself causes the dominant decay to be that of -2.5 as mentioned by Singh (1973) and discussed in 2.3.4. Only the high contrast horizontal plate shows finite conductor decay in the late time.
University of Pretoria etd – Combrinck, M (2006) Table 2: Summary of S-layer differential transform performance on synthetic models. (h = thickness, d =depth, l= side length of square plate and prisms) Cumulative Imaged Conductivity vs Model Comments Conductance vs depth depth Good approximation (12% Half space Smoothly σ = 0.02 S/m with depth Two Layers σ1= 0.02 S/m σ2 = 0.002 S/m h1 = 200 m Two Layers σ1= 0.02 S/m σ2 = 0.
University of Pretoria etd – Combrinck, M (2006) σLayer = 0.2 S/m dLayer = 150 m hLayer = 15 m Conductive layer in half space (varying σ contrast) Layer depth overestimated σHS= 0.02 S/m proportional σLayer = 2 S/m Decreasing depths with initial and increasing times conductivity to contrast; decrease of before σLayer = 10 S/m increasing to dLayer = 150 m erroneously high values.
University of Pretoria etd – Combrinck, M (2006) 200 m, 250 m, 300 m can be mistaken for two hLayer = 20 m layer earth. Conductive layer in half space (varying Host rock conductivities host rock cond.) < 0.01S/m results in the σHS= 0.0002 S/m, depths decreasing with 0.005 S/m, 0.0067 time S/m, 0.01 S/m, 0.02 conductance S/m, 0.04 S/m and although the extent of 0.1 S/m. this reversal is less than σLayer = 0.
University of Pretoria etd – Combrinck, M (2006) σPlate = 0.2 S/m conductivities l Plate = 100 m, 200 m, prism. below 300 m, 400 m dPlate = 150 m Conductive prism in half space (varying hor. dimensions) σHS= 0.02 S/m σPlate = 2 S/m l Plate = 100 m, 200 m, 100m still not resolved. Decreasing depth with increasing time for 300m and 400m prisms. Behaviour similar to infinite high contrast plates with overestimation of depths High contrast. and negative conductivities below prisms.
University of Pretoria etd – Combrinck, M (2006) Chapter 5 5 APPLICATION TO FIELD DATA "The bitterness of low quality remains long after the sweetness of low price is long forgotten.” (Benjamin Franklin, 1706-1790) 5.1 Introduction This chapter contains results of S-layer differential transform applied to two data sets, one from a ground survey and one from an airborne survey.
University of Pretoria etd – Combrinck, M (2006) Component: Vertical (z) Synchronization: Reference cable. Power Supply: 1,000W 110/220V, 50/60 (Hz single-phase motor-generator) Current Waveform: Bipolar rectangular current with 50% duty cycle Effective surface area of receiver coil: 100m2 Receiver Size: 34 x 38 x 27 cm Figure 5-1: Mountain with TDEM survey team.
University of Pretoria etd – Combrinck, M (2006) Figure 5-2: Grid locality and layout. 5.2.2 Objective Based on the TDEM and other investigations (including geochemical and structural geological interpretations) some exploration boreholes were drilled and follow-up borehole TDEM surveys were done. This chapter is not intended to be a discussion of the exploration program or to propose a geological model for the area.
University of Pretoria etd – Combrinck, M (2006) noise or geological noise. Whatever the cause, noise in data will produce noise in the processed product and in extreme cases may even cause a technique to fail. The S-layer differential transform is especially sensitive to noise because of the numerical differentiations performed. In addition to the optimal smoothing of data (chapter 4) a filter is also applied to remove noisy data points from each sounding before the transform is applied.
University of Pretoria etd – Combrinck, M (2006) Figure 5-3: Line 4950, Station 100. Top: Raw data with calculated cumulative conductance and imaged conductivity. Middle: No filter effect on input data values, only on cumulative conductance curve with imaged conductivity of filtered conductance values. Bottom: Input data filtered for late channel erratic behaviour and filtered cumulative conductance values.
University of Pretoria etd – Combrinck, M (2006) Figure 5-4: Line 4950, Station 300. Top: Raw data with calculated cumulative conductance and imaged conductivity. Middle: No filter effect on input data values, only on cumulative conductance curve with imaged conductivity of filtered conductance values. Bottom: Input data filtered for late channel erratic behaviour and filtered cumulative conductance values.
University of Pretoria etd – Combrinck, M (2006) Figure 5-5: Line 4950, Station 400. Top: Raw data with calculated cumulative conductance and imaged conductivity. Middle: No filter effect on input data values, only on cumulative conductance curve with imaged conductivity of filtered conductance values. Bottom: Input data filtered for late channel erratic behaviour and filtered cumulative conductance values.
University of Pretoria etd – Combrinck, M (2006) Figure 5-6: Line 4950, Station 450. Top: Raw data with calculated cumulative conductance and imaged conductivity. Middle: No filter effect on input data values, only on cumulative conductance curve with imaged conductivity of filtered conductance values. Bottom: Input data filtered for late channel erratic behaviour and filtered cumulative conductance values.
University of Pretoria etd – Combrinck, M (2006) Figure 5-7: Line 4950, Station -1550. Top: Raw data with calculated cumulative conductance and imaged conductivity. Middle: No filter effect on input data values, only on cumulative conductance curve with imaged conductivity of filtered conductance values. Bottom: Input data filtered for late channel erratic behaviour and filtered cumulative conductance values.
University of Pretoria etd – Combrinck, M (2006) 100 (Figure 5-3) contains four data points at the end that are filtered out. No data are discarded by the SDTC filter and therefore the first two options yield identical results.
University of Pretoria etd – Combrinck, M (2006) Figure 5-8: Comparison of SDTC filter only (top) and SDTC with additional noise filter (bottom). Black dots are station elevations (DTM) and white dots represent depths at which conductivities are calculated. 5.2.4 Comparison of 25Hz (high, H) and 6.25Hz (medium, M) base frequency data The high frequency time channels range from 0.088ms to 6.978ms and the medium frequency channels from 0.35ms to 27.92ms.
University of Pretoria etd – Combrinck, M (2006) will be noisier than the other in the overlapping range. If data quality is good for both frequencies, the conductivity depth sections obtained from the different frequencies should also overlap for intermediate depths with the high frequencies adding shallower data and the medium frequencies contributing to the deeper parts of the sections.
University of Pretoria etd – Combrinck, M (2006) The top of the conductor is defined better by the high frequency. The medium frequency shows behaviour as in Figure 4-44 where it was found that when a conductor is shallower than the depth to where the 1st channel would plot in the surrounding half space (compare the depths of the first channel plots on the rest of the line), the cumulative conductance and conductivity curves are distorted.
University of Pretoria etd – Combrinck, M (2006) Figure 5-10 shows an example of poor correlation between conductivity depth sections for the two frequencies. In block A conductors are mapped on both frequencies but with more than 100m discrepancy in depth. In block B a conductor is mapped consistently over at least 4 stations on the medium frequency, but nothing is seen on the high frequency although this depth range is well covered. The question is where exactly these discrepancies originate.
University of Pretoria etd – Combrinck, M (2006) Figure 5-12: Line 1650; Stations -200, 150 and 250; medium and high frequency measured data. 5.2.5 Imaged conductivity sections Figures 5-13 and 5-14 show screen dumps of a 3-D presentation of the complete data set as a series of imaged conductivity – depth sections plotted underneath the station positions which are draped over the DTM.
University of Pretoria etd – Combrinck, M (2006) values. A final filter is applied keeping only values between -5 and 5S/m to grid and contour. The contouring colour scheme is fixed for all sections and assigns dark blue to all negative values and a logarithmic scale from light blue (0S/m) to magenta (5S/m) for positive values.
University of Pretoria etd – Combrinck, M (2006) Conductor decay constant [s] (Draped over topography) Imaged Conductivity [S/m] (Sections) Figure 5-14: .3D view from inclination 60˚, declination 180˚ and 5km distance with and without contour map of conductor decay constants.
University of Pretoria etd – Combrinck, M (2006) In the following section one area of interest will be isolated and compared with plate modelling results. 5.2.6 Comparison of automated conductor location with Maxwell plate model results The results of the automated processing and conductor location of line 4050 are presented in Figure 5-15. At the very top, the profile data are shown for channels 1-10 and channels 11-20 respectively.
University of Pretoria etd – Combrinck, M (2006) Figure 5-15: Line 4050. EM response profiles and sections from automated processing procedures.
University of Pretoria etd – Combrinck, M (2006) Figure 5-16: Line 4150. EM response profiles and sections from automated processing procedures.
University of Pretoria etd – Combrinck, M (2006) Figure 5-17: Line 4050. Comparison of Maxwell plate model and conductivity depth section. Figure 5-18: Line 4150. Comparison of Maxwell plate model and conductivity depth section.
University of Pretoria etd – Combrinck, M (2006) 5.3 5.3.1 Airborne survey Data acquisition and system parameters The airborne data were acquired with the VTEM system. The VTEM is a helicopterborne TDEM system with central loop configuration developed by Geotech. One line is used to demonstrate the use of the S-layer transform. The data are presented here courtesy of BHP Billiton.
University of Pretoria etd – Combrinck, M (2006) 4 EM Response (pV/Am ) Channels 1-13 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 4 EM Response (pV/Am ) 0 2800 3000 3200 3400 3600 Distance [m] Channels 14-27 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 3200 3400 3600 Distance [m] Figure 5-19: EM Response over conductor. 5.3.
University of Pretoria etd – Combrinck, M (2006) underneath the conductor where data not complying to the S-layer transform assumptions were filtered out (indicating high conductivity contrasts). Elevation above sea level [m] Distance [m] Figure 5-20: Conductivity depth section from S-layer transform, showing dipping conductor. Elevation above sea level [m] Distance [m] Figure 5-21: Conductivity depth section in greyscale with channels corresponding to half space power law decay indicated in red.
University of Pretoria etd – Combrinck, M (2006) Elevation above sea level [m] Distance [m] Figure 5-22: Conductivity depth section in greyscale with conductor decay constants plotted at scaled channel positions. Elevation above sea level [m] Distance [m] Figure 5-23: Conductivity depth section in greyscale with channels on stations showing sign changes indicated in blue.
University of Pretoria etd – Combrinck, M (2006) 5.4 Conclusions and recommendations The automated procedures outlined in chapter 4 can be implemented on both ground and airborne central loop configuration TDEM data. Filters to remove noise as well as clean data not conforming to the assumptions made in the S-layer differential transform can be applied efficiently in the time and spatial domains retaining the main advantage of the transform compared to inversion algorithms, namely speed.
University of Pretoria etd – Combrinck, M (2006) REFERENCES Barnett, C. T., 1984, Simple inversion of time-domain electromagnetic data. Geophysics, 49: 925-933 Theory. Elsevier Science Publishers, Amsterdam. Burden, R. L., and Faires, J., D., 1993, Numerical Analysis –5th Ed. PWS Publishing Company: 156-164 Marquardt, D. W., 1963, An algorithm for least-squares estimation of non-linear parameters: J. SAIM, 11: 431-441. Butler, D. K.
University of Pretoria etd – Combrinck, M (2006) Newman, G. A., Hohmann, G. W., and Anderson, W. L., 1986, Transient electromagnetic response of a threedimensional body in a layered earth. Geophysics, 51: 1608-1627 Elura orebody: Sydney, Austral. Soc. Expl. Geophys.: 130-139 Spies, B. R., and Frischknecht, F. C., 1991, Electromagnetic Sounding; in Nabighian, Misac N., Ed., Electromagnetic Methods in Applied Geophysics, Volume 2, Application: Soc. of Expl. Geophysicists: 285-425 Newman, G. A.
University of Pretoria etd – Combrinck, M (2006) inversion: J. Appl. Geophys.
University of Pretoria etd – Combrinck, M (2006) APPENDIX A Derivation of Simpson’s rule for unequally spaced data values (centre points). A Lagrange polynomial p(x) is obtained such that p(xi)=f(xi) for i=1,2,3 and integrated over the interval x1 < x < x 3 . p ( x ) = f ( x1 ) (x − x 2 )(x − x 3 ) + (x1 − x 2 )(x1 − x 3 ) (x − x1 )(x − x 3 ) + (x 2 − x1 )(x 2 − x 3 ) f (x2 ) f ( x3 ) (x − x1 )(x − x 2 ) (x 3 − x1 )(x 3 − x 2 ) (B.
University of Pretoria etd – Combrinck, M (2006) ( ) ( ) ⎡ 13 x 33 − x13 − ( x 2 + x 3 ) 12 x 32 − x12 + x 2 x 3 ( x 3 − x1 ) ⎤ ⎥ = f ( x1 ) ⎢ (x1 − x 2 )(x1 − x 3 ) ⎢⎣ ⎥⎦ ⎡ 13 x 33 − x13 − ( x1 + x 3 ) 12 x 32 − x12 + x1 x 3 ( x 3 − x1 ) ⎤ ⎥ + f ( x 2 )⎢ (x 2 − x1 )(x 2 − x 3 ) ⎢⎣ ⎥⎦ ⎡ 13 x 33 − x13 − ( x1 + x 2 ) 12 x 32 − x12 + x1 x 2 ( x 3 − x1 ) ⎤ ⎥ + f ( x3 )⎢ (x 3 − x1 )(x 3 − x 2 ) ⎢⎣ ⎥⎦ = f ( x1 )W1 + f ( x 2 )W 2 + f ( x 3 )W3 ( ) ( ) ( ) ( ) Derivation of Simpson’s rule for unequall
University of Pretoria etd – Combrinck, M (2006) and x3 ∫ x2 x3 f(x)dx ≈ ∫ x2 f ( x1 ) (x − x 2 )(x − x 3 ) + (x1 − x 2 )(x1 − x 3 ) ( ) f (x2 ) (x − x1 )(x − x 3 ) + (x 2 − x1 )(x 2 − x 3 ) ( f ( x3 ) (x − x1 )(x − x 2 ) dx (B.
Oasis montaj 6.3 Viewer The core software platform for working with large volume spatial data QUICK START™ TUTORIAL www.geosoft.
The software described in this manual is a completely free software environment that you can distribute freely to any recipient with whom you need to share your earth science results and ideas. Manual release date: 26/04/2006. Written by, Nancy Whitehead. Please send comments or questions to info@geosoft.com Copyright © Geosoft Inc. 2006. All rights reserved.
Contents Oasis montaj 6.
Opening a Database 15 Adding Compression to your Database 16 Displaying Data Files in an Oasis montaj Database 16 Displaying Channels (Columns) in the Spreadsheet 18 Displaying Basic Channel Statistics 20 Displaying Profiles in the Spreadsheet 21 DataBase Tool Bar 23 Profile Panel Options 23 Plotting Profile Windows 24 Metadata Tool Data Types 25 25 Drag-n-Drop 27 Oasis montaj Maps 28 Displaying a Map 28 Adding Map Comments 28 Using the Map View/Group Manager Tool 28 Rendering
Grid Report and Statistics 52 Sending E-maps 53 Unpacking an E-map 54 Exporting Data 54 Exporting Databases 55 Export Geosoft XYZ Data Format 55 Export CSV Format 56 Exporting Maps 56 Printing Maps in Oasis montaj 57 Printer Setup 58 Print a Map 58 Appendix 1: Geosoft Concepts Oasis montaj Viewer 60 60 What is Oasis montaj? 61 Viewer Capabilities 61 Projects Data and Profiles Maps, Grids and Images Online Help and Technical Support 61 62 62 62 Keeping you in touch with your dat
Dynamically link data and information to knowledge 73 Geosoft Algorithms and Techniques 74 Process Maker technology links data processing 75 Appendix 2: Displaying Data Formats 76 Geosoft XYZ File Format 76 ASEG-GDF File Format 77 Geosoft GBN (Binary Data File) Format 78
Oasis montaj 1 Oasis montaj 6.3 Oasis montaj 6.3 is the latest release from Geosoft. Oasis montaj is available in two versions – a free Viewer and a licensed Mapping and Processing System. The Oasis montaj Viewer is a free software product that enables you to view Geosoft databases, Geosoft grids and a variety of common image and data exchange formats.
2 Oasis montaj requirements. Internet To use the Internet capabilities in Oasis montaj, you will need to install Internet Explorer 5.0 or later. This does not mean that you have to have Internet Explorer as your default browser; Oasis montaj just uses the Internet connection technology supplied in IE5 Installing Oasis montaj Viewer The Oasis montaj Viewer can be installed from a CD-ROM or downloaded from the web and installed via an EXE file.
Oasis montaj 3 3. When ready, the program displays the Geosoft Oasis Montaj Viewer – InstallShield Wizard Welcome screen. To continue, follow the directions on the screens that appear. 4. When the "Installation Completed" dialog is displayed, you can check the boxes provided to launch Oasis Montaj Viewer or view the release notes. 5. Click the [Finish] button to complete the installation process.
4 Oasis montaj All communication with the server saved in a log file on your local computer so that you can check to see what information was sent and received. This is the default setting Restricted This setting will not authorize any communication with the server. This means that you do not want any communication with the server to take place. With this setting, you will not be able to download any data from the server.
Oasis montaj 5 Finding More Help Information There are several other functions included in the basic Oasis montaj help system that may be useful to your work. The entire documentation for the system is available through the online help system. This electronic library of information enables us to constantly update the information and provide you with the most up-to-date information available.
Tutorial 1: Getting Ready to Work 7 Tutorial 1: Getting Ready to Work In this tutorial, we will guide you through the steps you need to know to start working with your new software. At this point you should have already installed Oasis montaj. You should begin by starting Oasis montaj. TO START USING OASIS MONTAJ 1. On the Start menu bar click Programs and then click Geosoft and then click Oasis montaj Viewer|Oasis montaj Viewer. or 2.
8 Tutorial 1: Getting Ready to Work Map file, including plots and grids *.MAP Geosoft grid file *.GRD Colour information for grids/images *.AGG Geosoft eXecutable *.GX Geosoft Script file *.GS Oasis Menu, Oasis sub-menu *.OMN, * .SMN Geosoft Project file *.GPF Geosoft projection information file *.GI Geosoft Map file (used in the MapInfo software to distinguish a Geosoft map file from a MapInfo (*.map) file *.
Tutorial 1: Getting Ready to Work 9 access the Tools window click the Tools bar on the bottom of the Project Explorer. To return to the Data window, click the Data bar on the top the Project Explorer. TO CREATE A PROJECT: 1. Start Oasis montaj. 2. On the File menu, click Project and then click New. The New Project dialog is displayed. Oasis montaj assumes that your data is in the directory containing this project 3. Specify a name and directory for the project.
10 Tutorial 1: Getting Ready to Work 5. To close a project, click File|Project and then click Close. Changing Default Settings The program will work correctly with all of the standard default settings; however these may be changed to reflect your personal requirements or those of your computer. The default settings are the selections made for many of the programs where there is no user input and are designed to yield logical results.
Tutorial 1: Getting Ready to Work 11 The following list summarizes the default settings: Default grid colour table Select the default colour table to use for displaying grids Print memory (megabytes) Select the amount of RAM you would like the Geosoft print driver to use when printing. This only effects print configurations that use the Geosoft drivers. Enter 0 to use the default, which is 33% of the total physical RAM available on the system.
12 Tutorial 1: Getting Ready to Work directory, and there must be sufficient room to hold the cache plus other Geosoft temporary files. The image cache should not be more than 50% of the available room in GEOTEMP. Temporary file directory This directory is used by Oasis montaj to store temporary files. Depending on the application, the requirements for storage in this directory can be VERY large (from 10 megabytes to gigabytes). We recommend setting this parameter to a very FAST drive.
Tutorial 1: Getting Ready to Work 13 Finding Help Oasis montaj provides help information through two different interfaces. The Online Help system can be used to locate quick information using contents, index and find search tools. For new users we recommend that you take the online tour included in the About topics, which will introduce you to Oasis montaj. The Manuals, Tutorials, and Technical Notes system (using Acrobat Reader 4.
Tutorial 2: Working with Data 15 Tutorial 2: Working with Data To a use Oasis montaj effectively, you will need to understand a bit about databases, spreadsheets, profiles and maps. The “window” to the database in Oasis montaj is a specialized earth science spreadsheet that appears automatically when you open a database. This spreadsheet provides access to a wide range of data management and profile viewing capabilities. Maps have special properties that you will learn about in later tutorials.
16 Tutorial 2: Working with Data 4. Select the tutorial database (casaber.gdb) and click [Open]. The casaber.gdb is displayed in your project. Adding Compression to your Database 1. On the Data menu, click Save database as. The Save database as dialog is displayed. 2. Specify a new database name (casaber_size.gdb). From the Compression Type dropdown list select (Size) click the [OK] button to continue. 3. The new database (casaber_size.gdb) is displayed in your project.
Tutorial 2: Working with Data 17 file. For more information about the Geosoft XYZ format and other file formats that can be displayed in an Oasis montaj database see Appendix 2: Displaying Data Formats. DISPLAYING AN XYZ FORMAT FILE IN A DATABASE 1. On the Data menu, click Open, and then click Geosoft XYZ. 2. The Open a Geosoft XYZ file into a new database dialog is displayed. 3. Using the [Browse] button locate the Geosoft XYZ file (xyz_format.xyz) in your project directory.
18 Tutorial 2: Working with Data Note: The default placeholder for missing or blank data (i.e. dummy value) in an XYZ file is “*”. Displaying Channels (Columns) in the Spreadsheet Unlike traditional spreadsheets, the Oasis montaj Spreadsheet windows provide a view of your database instead of the actual data in the database. This design enables you to customize the spreadsheet to display data to your specifications. TO REMOVE A CHANNEL (COLUMN) 1.
Tutorial 2: Working with Data 19 2. A box will appear beneath the empty channel header listing all the available channels that are not currently being viewed in the Spreadsheet window.
20 Tutorial 2: Working with Data 3. Select Z1 and click the [OK] button, to display the channel in the Spreadsheet. If you know the name of the data channel already, you can simply position the cursor on a specific Channel Header Cell, type the name and press the [Enter] key. Note: The symbol ‘**’ in a channel cell indicates that the data are too wide for the spreadsheet column. To change the width of a column, place the cursor on the dividing line between the column headers.
Tutorial 2: Working with Data 21 7. In the New statistics file box, specify a file name (xyz_F1_stats.txt). Click the [OK] button to save the file to your project directory. Then, click the [OK] button to close the Stat Report dialog box. The following list summarizes how to obtain results on specific parts of your database: Click once on the channel header cell to highlight the header cell. No statistics can be calculated.
22 Tutorial 2: Working with Data To see where the Z1 values are located on the profile line simply click on a value in the Mag channel and the system will show a box indicating the corresponding area on the profile. 3. We recommend you experiment with the various options available for profile display, appearance, scaling and plotting etc. available via the Profile menu, under Profile Options. Tip: TO DISPLAY A DIFFERENT PROFILE: 1.
Tutorial 2: Working with Data 23 Tip: When the Line Number Cell is highlighted, you can use the [Page Up] and [Page Down] keys from your keyboard to scroll through lines. You can also use the Database Tool Bar to scroll through the lines. The figure below shows what each of these buttons do. DATABASE TOOL BAR Display First Line/Group. Click this button to show the data and profiles for the starting line in your database. Display Last Line/Group.
24 Tutorial 2: Working with Data 2. The system will display the Panel Options dialog box. Make sure the Scale to fit for each line option button is selected and there is a check mark in the Same scale for all profiles in panel option box. The following list summarizes the different scale options available to you: Scale to fit for each line Adjusts the scale in the profile box to fit each line that is displayed. Fix the range Uses the same range for all the profiles that are displayed..
Tutorial 2: Working with Data 25 4. Click [OK]. The profile plot map (xyz_format_L350.map) is displayed in your project. Metadata Tool The Metadata Tool is a context-oriented, interactive method for viewing and editing attributes assigned to Geosoft data. Attributes (or metadata), information about data, can be simple or complex and the descriptive needs of different kinds of data are infinitely diverse.
26 Tutorial 2: Working with Data can exhibit attribute information for specific map elements. For example, a polygon contains specific attributes which are displayed if a polygon is the current selection (only permitted in map edit mode).Map views and groups exhibit different characteristics and the tool is adjusted with each context change.Map elements (polygons, lines, points, etc.) exhibit their own attributes depending on the context chosen.
Tutorial 2: Working with Data 27 3. The white letter in a grey circle to the left of the “Attribute” indicates the data value type; "i" for integers, "r" for real floating point numbers, "t" for text, and "o" for data objects. 4. Some information is contained in an object, which will normally display an object icon and object name as the Value. The CoordinateSystem attribute shown above is an example of an object. Objects can usually be edited or activated by doubleclicking on the object value.
28 Tutorial 2: Working with Data Oasis montaj Maps In Oasis montaj, a Map is more than a printed sheet of information. Maps are special items that serve a number of purposes in the system. The map window provides the basic mechanism for creating maps, displaying images, and linking to other maps and data. To work effectively with maps, you need to be familiar with the purposes of maps in the system as well as the role of Views and Groups. Maps use Views to organize and display information.
Tutorial 2: Working with Data 29 The effect of a double click on any item depends on the state of the map. If in shadow cursor mode the map will switch to either group or view selection mode and select the item that was clicked upon. If the map is already in either of these selection modes a button or using the activate double click has the same effect as hitting the shortcut key (default key).
30 Tutorial 2: Working with Data OTHER TOOL OPTIONS The other Tool options include moving, masking, transparency settings, editing and deleting. All of the following properties require the licensed version of Oasis montaj. Frozen Scale Click this button to freeze the scale of the currently selected map group, independent of the view scale of the map. For example, when zooming in the text size in a group will not grow but remain the same size on the screen.
Tutorial 2: Working with Data 31 changes and revert to the original map. Using the Viewer Tool Bars The following Tool Bars can be displayed in the Oasis montaj Viewer. Note that the Database Tool Bar can be found on page 23. To Show|Hide tool bars, on the Tools tab of the Project Explorer select the tool bar of interest, right-click and select Show|Hide from the popup menu. STANDARD BAR Open Database Use this command to open a previously defined Oasis montaj database.
32 Tutorial 2: Working with Data Shadow Cursors with Dynamic Link Click this button to create a dynamic link between one or more maps and data (in Spreadsheet and Profile windows) to assist in locating and comparing data, profiles and maps. If you have plotted flight lines on your map, you can use this button to dynamically link the map to the database and profiles. When you move the Shadow cursor on the map, the database and profile views will update to show the corresponding data.
Tutorial 2: Working with Data 33 Pan (Default Shortcut: P-Key or Spacebar) Click this button to move around in the currently selected map. Click the left mouse button and while holding the button down, move the hand cursor to pan around the current map area. You can also access this command by clicking the right mouse button on a map and selecting Pan from the popup menu. Interactive Zoom (Default Shortcut: Shift-Z) Click this button to activate the interactive zoom.
34 Tutorial 2: Working with Data Full Map (Default Shortcut: F-Key) Click this button to display the whole map area in the map window. You can also access this command by clicking the right mouse button on a map and selecting Full Map from the popup menu. Zoom Level Control This option enables the user to specify an estimation percentage of print size on screen (100%) or various other levels (for example, 400%, 200%, 100%, 75%, 50% and 25%).
Tutorial 2: Working with Data 35 Displaying Grids and Images on a Map In Oasis montaj, grids and images are always displayed on a map in the Map window. There are several types of grids and images you can display. For a complete list of the grid and image formats that are supported in Oasis montaj see the online help topic Data Exchange formats. In Oasis montaj, a Grid is a visual representation of a survey area interpolated from a series of survey points.
36 Tutorial 2: Working with Data 2. Select the Grid name (casaber.grd), Colour method, Colour table, Brightness, Contour interval, and the Location. For more information on these parameters click the [Help] button. 3. Click [New Map]. The grid is displayed on a new map. Note: To display a grid on a current map, click the [Current Map] button. DISPLAYING AN IMAGE ON A MAP 1. On the Map menu, click Display, and then click Image (bmp, tiff, etc.). The Place an Image on a map dialog is displayed. 2.
Tutorial 2: Working with Data 37 Data Access Protocol (DAP) DAP is a technology that enables efficient transfer of high volume spatial data from a designated DAP data server to a DAP client via the Internet or an Intranet. There are two types of DAP clients, a thick client (a desktop software application) and a thin client (web browser). Oasis montaj, MapInfo and ArcGIS are thick DAP client software applications.
38 Tutorial 2: Working with Data 2. Specify in Longitude/Latitude the data range you want to download and display. Click the [Next>] button. The Create a new map dialog is displayed. 3. Specify the map parameters: Map name, Map template, Map scale (by clicking the [Scale] button the default map scale - based on the data range and map template - will be displayed), and Map Titles. Note that, the default map projection is displayed in the Coordinate system box. 4. Click the [OK] button to display the map.
Tutorial 2: Working with Data 39 5. On the DAP menu, click Get DAP data. The Authorize Internet Communication dialog is displayed (Note: If you Internet Trust Configuration is set to "Trusted" this dialog will not appear). 6. Click the [Authorize] button to query the DAP server to determine what grid data the DAP server has that matches the data view of the current map. The Get DAP Data dialog will be displayed.
40 Tutorial 2: Working with Data 7. Select the data you wish to download (e.g. Topography) and click the [Get Data] button. The DAP Data Options dialog is displayed.
Tutorial 2: Working with Data 41 8. Use this dialog to specify the parameters for your data. For more information on the data options, click the [Help] button. 9. Once you have specified your data options, click the [OK] button to download and display the DAP data on your current map. 10. Once the download is complete, the Get DAP Data dialog will again be displayed. Click the [Exit] button to close the window. The gridded data will be displayed in your open map.
42 Tutorial 2: Working with Data Note: Oasis montaj licensed users have access to a variety of DAP display technology features including; Re-project the grid to the projection of the current map view, Re-project and resample the grid to a specified resolution, Save the grid in the native projection format, Display the grid as a simple colour image, Display the grid as a shaded colour image, and Download and save only, do not display the grid.
Tutorial 2: Working with Data 43 Data: The Data branch contains all metadata associated with any spatial data type. The information at the "Data" level is common to all types of spatial data. Grid: This example describes a grid of data; hence there is a "Grid" branch, which contains metadata that is specific to grids. Display: Grids may contain display information about the grid data set, which is stored in the "Grid|Display" branch.
44 Tutorial 2: Working with Data - enables you to modify the overall view of the 3D View on a map - enables you to modify the individual planes within each 3D View - enables you to add labels, axis, and a box around the 3D View - enables you to adjust the rendering resolution in the 3D tool - enables you to modify the voxel display parameters in the 3D tool View Tab The View tab enables you to: • Rotate your 3D View 360 degrees in all directions • Zoom in and out of the displayed View • Use the Pan t
Tutorial 2: Working with Data 45 2. Left click, and while holding down on the mouse key move to the right to zoom in and to the left to zoom out. TO USE THE PAN TOOL: When you select the Pan button the curser changes to the pan mode, and enables you to move the entire displayed grid. 1. Select the Pan button. The curser changes to pan mode ( ). 2. Left click, and while holding down on the mouse key move the grid right to left or up and down.
46 Tutorial 2: Working with Data Planes Tab The Plane tab enables you to: • Select the Plane to modify • Select the plane Offset in Z units relative to the plane coordinates.
Tutorial 2: Working with Data 47 detail at the expense of performance. You can select a number up to 768 (you entry will be converted to an even multiple of 16). Press the [Enter] key. The relief grid will be redrawn in the 3D viewer with the new sample resolution. TO SPECIFY THE BASE VALUE OF THE RELIEF GRID: 1. In the Base box, specify the base value of the relief grid. Press the [Enter] key. The relief grid will be redrawn in the 3D viewer with the new base value.
48 Tutorial 2: Working with Data Axis Tab The Axis tab enables you to: TO • Add a box around the 3D View display • Add an axis to the 3D View display • Specify the X axis label • Specify the Y axis label • Specify the Z axis label ADD OR REMOVE AN AXIS ON MY 3D V IEW : The Axis check box enables you to draw an X, Y and Z axis on the View display. 1. Click the Axis check box to add or remove the X, Y, and Z axis on the View display.
Tutorial 2: Working with Data 49 • Full rendering occurs every time you modify the 3D view and the view is redrawn. • Fast rendering occurs when the image is in constantly motion for example while rotating, zooming or panning. • The 3D Views rendering process makes heavy use of the available memory on your video card, and performance will be substantially reduced if your limits are exceeded.
50 Tutorial 2: Working with Data Use the 3D Voxel tab to modify the voxel display parameters in the 3D tool.
Tutorial 2: Working with Data 51 2. This button works as a toggle you can toggle on or off the Voxel box. TO DISPLAY VOXEL GRID LINES: 1. Click the display Voxel grid lines ( ) button and the Voxel colour shading will be removed/added and the Voxel grid/Voxel colour fill will be displayed. 2. This button works as a toggle you can toggle on or off the Voxel grid lines or colour shading. TO DISPLAY VOXEL CONTROLS DIALOG: 1.
52 Tutorial 2: Working with Data Fast render resolution: The fast render resolution moves 128k to the video card at the low range, 2 Mb at the middle range and 24 Mb at the high range. This means that every time you draw in FAST mode you move that much memory to the video card. Unfortunately, if your memory bandwidth is low or your video card is not very fast this slows down the rendering time.
Tutorial 2: Working with Data 53 4. Click the [Stats] button to view the Grid statistics report dialog. 5. Click the [
54 Tutorial 2: Working with Data are included in the e-mail. When you open an e-map in Oasis montaj, all the information can be read in this format by all related functions, such as grid statistics. 1. Select (highlight) the map you want to send. 2. On the Map menu, click Send map to. 3. A new e-mail is composed in your default e-mail program with an attached e-map file.
Tutorial 2: Working with Data 55 Exporting Databases Oasis montaj Viewer enables you to export Oasis databases in a variety of data formats. This tutorial will describe how to export to a Geosoft XYZ and CSV Data format file. Export Geosoft XYZ Data Format The directions below describe how to export a database as a Geosoft XYZ file. 1. Select the Casaber.gdb database in your current project. 2. On the Data menu, click Export, and then click Geosoft XYZ. The Export XYZ data dialog box is displayed. 3.
56 Tutorial 2: Working with Data increment), and to include (or not include) dummies, comment headers, line headers, and CSV formatting. 4. You can specify a Template name (Export_XYZ.o0) or use the default (default.o0) template. 5. Click [OK] to return to the Export XYZ data dialog, click [OK] to export the data as Export_XYZ.xyz. Export CSV Format 1. Select the Casaber.gdb database in your current project. 2. On the Data menu, click Export, then click Other.
Tutorial 2: Working with Data 57 3. In the Image Type box, choose the Output Format as (TIFF (*.tif)) and select the Colour Depth (True Color (24-bit)) 4. In the Region to Export box click the (Full Map) option. 5. In the Image Resolution box, change the Pixel Size to 35.75. Note: Pixel Size is the number of ground units each pixel in the image represents. In the example above, each pixel in the exported map represents 35.75 meters. You can set the pixel size to match the grid cell size closely*.
58 Tutorial 2: Working with Data If you are not satisfied with your driver's performance, you can try selecting; Geosoft bands, Geosoft bands and dither, HP-RTL or the Postscript printing option. Refer to the on-line help system for a complete discussion on the pros and cons of the different printing modes.
Tutorial 2: Working with Data 59 2. On the File menu, click Print. The system displays the Print dialog box. 3. In the Select Region to Plot box select Entire Map. In the Plot Scale box select Fit To Page. Note: Map may not be plotted to scale. To maintain the map scale, select the Use Scale Factor option and specify a value, (1 = 100%). If you use this option, the map may require more than one page depending on the media to which you are printing or plotting. 4. In the Panels box, select All.
60 Appendix 1: Geosoft Concepts Appendix 1: Geosoft Concepts This chapter contains information about the components included in Oasis montaj™ and describes the concepts you will need to know to use the system. A quick overview of the concepts described in this chapter are available in the Oasis montaj Viewer help system in the About directory called Tour for New Users. Oasis montaj is Geosoft’s core software platform for working with large volume spatial data.
Appendix 1: Geosoft Concepts 61 What is Oasis montaj? The concept of an integrated environment for earth science data emerged from over two decades of software development at Geosoft and is now implemented in the Oasis montaj software platform.
62 Appendix 1: Geosoft Concepts DATA AND PROFILES • • • • • • Open new databases imported from Geosoft GDB, Geosoft GBN, Geosoft XYZ and ASEG-GDF formats Export databases as Geosoft GDB, Geosoft GBN, Geosoft XYZ, ASEG-GDF, CSV (Excel), ODDF (USGS), POST PC (USGS) and POST UNIX (USGS) Show and plot data profiles in upto five database profile windows View data projected coordinate system information View data statistics and historical processing logs Dynamically link data between spreadsheet, profile window
Appendix 1: Geosoft Concepts 63 Keeping you in touch with your data An important design strategy in Oasis montaj was to keep you in touch with your data.
64 Appendix 1: Geosoft Concepts Projects and the Project Explorer To work in Oasis montaj requires an open Project. An Oasis montaj "Project" encompasses every item in your working project; from the data files in your project (databases, maps, and grids), to the tools used (including auxiliary tools such as histograms, scatter plots etc.
Appendix 1: Geosoft Concepts 65 • Tools; 3D Tool, Metadata Tool, Project Explorer and Undo/Redo Tool and the View/Group Manager Tool. • Toolbars; Database Tools Bar, Map Tools Bar, Navigation Bar and Standard Toolbar. Also available with the licensed version, Map Edit Tools Bar, Polygon Tools Bar and Script Bar. • Auxiliary Tools: Histograms, Scatter plots, Probability plots and Triplots (licensed version only).
66 Appendix 1: Geosoft Concepts Databases and high-volume data processing Many commercial and governmental groups currently use Oasis montaj for routine processing of high volume datasets (tested up to 10 gigabytes) and also for relatively low volume processing in a variety of mapping and other applications. One key to the system’s capabilities is the proprietary 3-dimensional database architecture, which enables the rapid processing and analysis of high volume data.
Appendix 1: Geosoft Concepts 67 Organized in lines (or groups), columns and elements, the database stores all data values of a particular type in individual columns or channels. This enables stand-alone processing of columns and eliminates the need to write results to interim storage areas and then re-write them after processing. The result is a significant increase in processing efficiency.
68 Appendix 1: Geosoft Concepts Spreadsheets are the windows to your database When you create or open a database, you see a spreadsheet. The Spreadsheet view is your “window” to the Oasis montaj database and it also provides you with flexibility in setting up your working environment. All data is stored securely in the underlying database — you simply decide which data you want to display in the spreadsheet and keep all other data in the background, hidden from view.
Appendix 1: Geosoft Concepts 69 • The ability to process selected samples, selected channels and selected lines or groups How the Spreadsheet Displays Project Data The spreadsheet does not display your actual data, but rather a view of the data. Depending on your type of project, the spreadsheet will display your data as either values or arrays. For surveys where a single value is recorded at each station, for example an assay survey, each data cell will contain a single value.
70 Appendix 1: Geosoft Concepts Profiles and viewing your data graphically The Profile view is your “graphical window” to the Oasis montaj database. You can display profiles of one or more variables in your database simply by selecting the channel and selecting a simple menu item. The profile appears directly below its corresponding database in a profile window. You can have up to five “panes” with 32 variables in each pane.
Appendix 1: Geosoft Concepts 71 Maps are more than printed sheets of information Geosoft’s mapping capabilities are the result of more than a decade of programming development, and the options for producing and editing maps — as well as the quality of output — reflect this level of experience. You can use the system to produce a variety of professional presentations quickly and easily.
72 Appendix 1: Geosoft Concepts from the Map View/Group manager. These transparency settings affect both 2D raster images and vector line work. As you use the system, you will become familiar with the information that is stored in each type of View and how to manipulate them (for example, by turning off a map layer for plotting purposes).
Appendix 1: Geosoft Concepts 73 Dynamically link data and information to knowledge Dynamic links are a key part of Geosoft’s strategy of helping professional’s stay in close touch with their data—from import to processing to analysis. By definition, dynamic links are interactive graphical connections that you can activate between databases, profiles and any number of maps in your project.
74 Appendix 1: Geosoft Concepts Geosoft Algorithms and Techniques The Geosoft eXecutable (GX) is the basic mechanism through which Geosoft provides the basic resources for all Geosoft Applications and Tools. GXs are programmed processes that are attached to the main menus in the system and to the special menus used in application suites. GXs run interactively in the graphical user interface but many GXs can also run in batch mode (using script commands). All Geosoft GXs are signed.
Appendix 1: Geosoft Concepts 75 Process Maker technology links data processing A dynamic process link is a built-in feature that remembers the processing parameters associated with a specific object such as a channel, grid or map and that enables you to quickly rerun the process using different settings. A quick tool for reprocessing data, the process link is also useful for remembering processing settings.
76 Appendix 2: Displaying Data Formats Appendix 2: Displaying Data Formats Oasis montaj Viewer enables users to display various file formats (Geosoft XYZ, Geosoft GBN, and ASEG-GDF) in an Oasis montaj database. Geosoft XYZ File Format The following is an example of a Geosoft XYZ file format: Line 290.0 10517.0 10517.0 10516.0 10515.0 10515.0 10514.0 10514.0 10513.0 10512.0 10512.0 8013.0 7977.0 7940.0 7904.0 7867.0 7831.0 7794.0 7758.0 7721.0 7685.0 56600.4 Line 300.0 10209.0 10209.5 10210.0 10210.
Appendix 2: Displaying Data Formats 77 ASEG-GDF File Format Following is an example of an ASEG-GDF import template: [IMPORT ASEG-GDF] DEFN BOOTHILL.dfn DATA BOOTHILL.
78 Appendix 2: Displaying Data Formats Geosoft GBN (Binary Data File) Format The following is an example of a Geosoft GBN file format: A Geosoft Binary Data file (.GBN) contains survey data in a binary format that can be imported directly into an Oasis montaj™ database. The format is intended for programmers who wish to design output data files that can be easily imported into an Oasis montaj database. //--------------------------------------------------------------// // gbn.
Appendix 2: Displaying Data Formats 79 // The first 17 characters of the comment header must be: // // "Oasis BINARY DATA" // // Any amount of ASCII text may follow. Oasis montaj will start reading // binary data at the first byte after the first <1A> byte. // // The file structure is as follows: // // Oasis BINARY DATA // required first 17 bytes. // comment text // As much ASCII text as // . // desired can be placed // . // in the comment header. // . // // <1A> // end of ASCII comments.
80 Appendix 2: Displaying Data Formats // you have defined three channels, they will be numbered 0, 1 and // 2. Channel data records can be in any order(i.e. 0,1,2 or 1,0,2) // and you do not need to specify all channels on every line. // // If the channels already exist in the database, the channel // parameters are ignored. // //-------------------------------------------------------------// // Example: // // Hex values are in , other binary values are in (value, // value,...).
Appendix 2: Displaying Data Formats 81 // 642 [<01> ("EM_I",4,0,10,0) ] EM inphase // 723 [<01> ("EM_Q",4,0,10,0) ] EM quadrature // 808 [<04> ("Spec",1,256,0,6,0) ] 256-channel spec. // 804 [<02> (100,0,0,10,1995,1,19) ] line 100 // 889 [<03> (0,4,1000.0,1.0,3610) (data,data, 3610 times) ] Time data // 15358 [<03> (1,5,1000.0,1.0,3610) (data,data, 3610 times) ] X data // 44267 [<03> (2,5,1000.0,1.0,3610) (data,data, 3610 times) ] Y data // 73176 [<03> (3,4,1000.0,0.
82 Appendix 2: Displaying Data Formats #define GS_LONG 3 // signed 4-byte integer #define GS_FLOAT 4 // 4-byte floating point #define GS_DOUBLE 5 // 8-byte floating point // A string type is indicated by the negative string length. For example, // a 10 byte string would be type -10. String data should be NULL // terminated.
Appendix 2: Displaying Data Formats 83 typedef struct { long lLineNumber; long lLineVersion; long lLineType; // one of LINE_? long lFlight; long lYear; long lMonth; long lDay; } GBN_LineRec; // record type <02> // --- data record --typedef struct { long lChanNumber; // number from channel list, 0 is first long lBinaryType; // incoming binary data type, one of GS_? double dFidStart; // start fiducial number double dFidIncrement; // fiducial increment long lLength; // number of data elements that follow // Fo
84 Appendix 2: Displaying Data Formats } GBN_ParameterRec; // record type <05> //---------------------------------------------------------------// BINARY TYPES // // Some of the data types in a GBN file have special usage in Oasis // montaj. These are: // // GSF_TIME 2 // Time (HH:MM:SS.SSSS) // GSF_DATE 3 // Date (YYYY/MM/DD) // GSF_GGRAPH 4 // Geographical (DEG.MM.SS.
Appendix 2: Displaying Data Formats 85 // *psMin = (short) (*psSec / 60); // *psSec = (short) (*psSec % 60); // // // --- Negative ? --// // return(sNeg); // } // // -------------------------------------------------------------// // static const short DateNGS[12] = {31,28,31,30,31,30,31,31,30,31,30,31}; // static const short DateLGS[12] = {31,29,31,30,31,30,31,31,30,31,30,31}; // // #define NORMAL_YEAR 365 // #define LEAP_YEAR 366 // // void // sBreakDate(double dVal, // Value to break // short *psYear, //
86 Appendix 2: Displaying Data Formats // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // // *psMonth = sMonth+1; *psDay = sDay+1; } -------------------------------------------------------------double dMakeTime(long lHour, long lMin, double dSec) { double dVal; // Hour Value // Minute // Second // --- Limit the Information --if (dSec > 30000000.0) dSec = 0.
Appendix 2: Displaying Data Formats 87 // // --- Get the Month --// // sMonth--; // if (sMonth < 0) sMonth = 0; // if (sMonth > 11) sMonth = 11; // // // // --- Get the Day --// // sDay--; // if (sDay < 0) sDay = 0; // if (sDay >= psMonths[sMonth]) sDay = (short) (psMonths[sMonth]-1); // // // // --- Add days in the previous months --// // i=0; // while (i < sMonth) sDay += psMonths[i++]; // // // // --- Compute the Value --// // return((double) sYear + ((double) sDay / (double) sDays)); // } #endif
