Using Horizontal Magnetic Dipole Sources to Improve AMT Data Quality within the “Dead Band”

Summary Due to the properties of natural high-frequency EM fields there is an inherent problem of obtaining high-quality AMT data in the frequency band from about ∼500 Hz to ∼5 kHz. To solve this problem, we propose using an additional artificial signal source when carrying out measurements using the AMT method. The source must be in the far-field zone and include several EM field polarizations. In this case, it becomes possible to obtain better data quality while remaining within the framework of the regular AMT method. In the course of this work, we have developed an EM field source consisting of two horizontal magnetic dipoles oriented in orthogonal directions and creating several field polarizations, which allows tensor AMT measurements. The main features of the proposed transmitting system include the ease of its deployment, the relatively low required power of the generated signal, synchronization of the generated signal with the working schedule of the AMT station, and a fully automatic signal generation mode that does not require operator intervention during surveying. Field tests of the system have shown its effectiveness in relatively conductive regions.