Geology Reference
In-Depth Information
Automatic data loggers, whether 'built-in' or attached, are essential rather
than optional if instruments are dragged, pushed or carried along a traverse
to provide virtually continuous readings. In many cases, all that is required
of the operators is that they press a key to initiate the reading process,
walk along the traverse at constant speed and press the key again when the
traverse is completed. Additional keystrokes should be used to 'mark' the
passing of intermediate survey points on lines more than about 20 m long,
but even this can be made unnecessary by integrating a DGPS unit (see
Section 15.2) into the system. Many instruments can now record GPS data
and can be synchronised using the GPS signal as a common time reference,
enabling on-the-move recording to almost 1-metre positional accuracy with
relatively cheap systems and without significant loss of data quality (Figure
1.15). Apart from the obvious productivity benefits of lines being traversed
more quickly and survey grids being set out in significantly less time, the
permanent record of where the instrument has actually measured data is
valuable for quality control.
Figure 1.15 Magnetometer coupled to a differential GPS navigation system
for continuous profiling. Unless allowance is made in processing for the
offset between the GPS and magnetic sensors, anomaly locations will be
incorrectly plotted (photo courtesy of Geometrics).
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