Specifications

University of Pretoria etd – Combrinck, M (2006)

[V/s]. voltagemeasured of derivative time

[V] loopeiver ideal recof force iveelectromot

[s] time

coil receiver of turns ofnumber

[marea receiver

[Amr transmitte ofmoment dipole magnetic

[m] depth

[S] econductanc cumulative

here

′

⎟

⎠

⎞

⎜

⎝

⎛

∂

∑

−==

∑

]

The time derivative of the measured voltage (|V|’) is the parameter that has to be

determined through numerical differentiation. This value is used to calculate both

cumulative conductance (S) and depth (d) of an equivalent S-layer for each time channel

and noise generated by differentiation will consequently be introduced into both these

numbers. However, in order to find the earth parameter of interest, conductivity (σ),

another numerical differentiation has to be performed as,

(4.3) ]

[Siemens.m

∂

=)(

which follows from the definition of cumulative conductance. Thus, not only is a new set

of errors generated in this step, but all errors from the first differentiation are carried over

and enlarged by this second differentiation.

The following features are investigated:

• three numerical differentiation techniques are analysed in terms of the

specific nature of TDEM data, as described above

• the most appropriate use of smoothing filters

• the effects of the re-sampling of data points to equal time intervals.