User's Manual

12-Survey & Map Mode Noggin
82
12.2.11.3Target of Known Depth
If there are no suitable hyperbolas visible in the data to perform the Hyperbola Matching
described above, it may be the situation that there is a target of known depth in the area being
scanned. If this is the case, selecting the button with the circle with a horizontal line through it will
superimpose a horizontal line on the data. This line can then be moved up or down until it lies on
top of the Noggin response to the known target. Then, the user can adjust the velocity value up
or down until the known target depth is correct. Once the depth is matched, the current velocity
value is the one used for all subsequent data acquisition.
(a) (b)
Figure: 12-6 Using a target of known depth to extract velocity. After selecting CALIB, choosing the
known depth button (a circle with a horizontal line through it) will superimpose a horizontal line on the
data (a). Using the depth buttons, this line can then be moved up or down until it lies on top of the
Noggin response to the known target (b). Then, the user can use the velocity buttons to adjust the
velocity value up or down until the known target depth is correct. Once the depth is matched, the
velocity value should be used for all subsequent data acquisition.
If units are metres then depths will appear in metres and velocities in metres per nanosecond (m/
ns). If units are feet then depths will appear in feet and velocities in feet per nanosecond (ft/ns).
To change units see Depth Units on page 85.