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1. The use of a controlled-source transmitter will provide signal without worrying about the time
of day, weather conditions, etc.. It is always available and tends to be relatively strong
compared to natural-field signals.
2. Because the receiver can be band limited to acquire only the exact frequency of the
transmitter, you can work in more noisy environments than is possible with traditional MT and
AMT.
3. Acquisition time can be reduced since the source is strong and always available.
CSAMT disadvantages:
1. CSAMT transmitters generally cost more than $80,000 USD.
2. The acquisition band of CS transmitters tends to be limited to a low end of 0.1 Hz in order to
avoid near-field signal processing issues. This means very deep surveying (greater than 5 km)
generally cannot be done using CSAMT.
3. A CSAMT transmitter generally can transmit up to 1,000 Volts at anywhere from 2 to 30
Amps into the ground. This requires health and safety precautions to be strictly observed.
4. Often when lower frequencies are acquired they enter into the near field. This is mostly seen
in high resistivity sites when the transmitter is too close for far field measurements. If near-field
measurements are made the results cannot be trusted without including the transmitter
parameters into the processing.
In short MT and AMT work well in low-noise environments where good natural field signal is
available. CSAMT is preferable in more noisy areas when the depth of investigation can be
achieved with a band width of from 0.1 Hz to 10 kHz. In some areas signals approaching 0.01 Hz
can be used if the ground is conductive (< 10 Ohm-m) and the transmitter is powerful enough to
be placed at a great distance away (say 20 km).
