Applications
B2-4 ENVI-MAG Manual
Tuning
Sensor tuning is used to maximize the precession signal while minimizing the
effects of interfering electrical signals, such as power line harmonic frequencies
at 50 and 60 Hz.
The automatic sensor tuning function will free you from having to pay close
attention to the tuning details. However, this may lead to some potential trouble.
In areas where there are very large local anomalies with strong gradients or
electrical interference, the ENVI-MAG may lock onto those signals.
Automatic tuning is quite useful for mineral exploration surveys. This is primarily
due to the fact that these surveys are usually away from major electrical noise
sources and encounter large variations (in excess of ±1000 nT) of the magnetic
field over large distances.
Fixed tuning is recommended where small field variations are encountered or
where there is a greater possibility of strong electrical interference.
Fixed tuning is also recommended for base-station applications or for
exploration surveys where there are only low-intensity variations in the magnetic
responses. Environmental surveys are also prime candidates for fixed tuning
since they are usually conducted in areas of large cultural noise — electrical or
large magnetic gradients (due to the close proximity of the magnetic sources).
Survey mode
Once you have determined the degree to which you need noise removed from
the data, you will need to select the appropriate survey mode.
WALKMAG
The most commonly used mode of operation in environmental applications
is the WALKMAG mode. With the ENVI-MAG, the operator can take almost
continuous readings (at sampling rates of up to every 0.5 seconds) in this
mode. For a walking pace of 3 km (2 miles) per hour, data will be collected
at approximately every half a metre (or about every two feet). This tight
spacing of data is necessary for the very shallow targets that are usually
encountered in environmental applications. The next figure (Figure B15)
illustrates the set-up for a WALK-MAG survey
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