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GSM19 Series Magnetometers - Version 7
GEM Systems, Inc. Advanced Magnetometers
For more technical information, visit www.gemsys.ca
First
press
B-destination
on the unit with the
incorrect
time, and
then
press
A-source
on the unit
with the
correct
time. After the synchronization, the destination unit displays screen 59, while the
source unit displays screen 60.
SCREEN 59
SCREEN 60
04 II 95sa12:02:21.3
C or 1C
synch done =+-1ms
04 II 95sa12:02:21.3
C or 1C
You is able to check the time by pressing the
C
button on both mags simultaneously. This "freezes"
the time on the display for an easier comparison but the internal timer continues running.
Press
1 C
to return to main menu. After the aforementioned steps, time synchronization can be
inspected again at any time and on both mags. To do so from the Main Menu press
C-info
and then
press
F-time
. Press and hold the
F
key simultaneously on both units to freeze the time display.
5.9 APPLYING DIURNAL CORRECTIONS
Diurnal corrected data is obtained by combining the readings of a Mobile unit with the readings of a
Base Station unit. The diurnal correction is obtained from the following equation
corrected field = mobile field
-
base field + datum
The Datum is just a positive shift of the corrected data. It is normally set to the average or expected
magnetic field of the area, but it could also be set to any other positive value or to zero
Since the Base is a stationary unit, its changes of the magnetic field are only caused by diurnal
variations. The readings of the Mobile unit however, are influenced by the diurnal and also by the
local variations of the field encountered during the survey (anomalies). The Diurnal Correction
removes the diurnal variations from the Mobile data so the anomalies can be better appreciated.
The reference or criteria to combine the Mobile and Base readings is the time stamp of the readings.
•
If the time of the readings of the mobile unit exactly match the time of the readings of the Base
unit, the Diurnal Correction is performed directly according to the equation above.
•
If the times do not match, the magnetic field from the Base unit is obtained by linearly
interpolating the field of the two Base readings that are closest in time to the Mobile reading.
The best way of obtaining diurnal corrected data is by using a Base Station and a Mobile unit.