The electromagnetic methods of Earth exploration have considerable development last years in Ukraine. The magnetotelluric sounding (MTS) remains one of the most efficient geophysical methods for the study of the Earth's interior with depths from first tens of meters till several hundreds of kilometers. There are some important requirements to the corresponding instrumentation which has to cover the frequency range from DC to ∼ 10 kHz with as high as possible sensitivity.
This problem is discussed in details in the presentation. First, the magnetic sensor selection criteria are given which allow using appropriately the induction coil or flux-gate magnetometers. Next the peculiarities of super-wide band induction coil magnetometers design are presented. Finally two major challenges in the field - to get reliable data in the so called "dead band" (from ∼1 to 0.1 Hz) and to prolong the apparent resistivity plots till the periods ∼100 000 second and more - are discussed. The ways to complete both these problems and to develop a high-class magnetotelluric instrument (MTI) are outlined in the paper.
An essential development problem is how to upgrade the flux-gate magnetometers sensor in order to lower the sensitivity threshold till picotesla level for the "dead band" and to reach long-term stability at least ∼ ±1 nT per week, preferably to get both these advantages simultaneously.
Second problem in sensorics is proper construction and methodology of use of non-polarized electrodes for electric field measurement in order to get as high as possible their own potential stability and low transient resistance.
And last but not least problem is data processing. A quick algorithm of robast processing of big amount of data (up to 3000000 samples from each measuring channel) is realized and user friendly software is created. It allows to carry out data and instrumentation parameters correction, calculation of transfer function and construction of MTS curves.
The modern state of the art in all these directions is analyzed and the best achieved results are given. The experimental data of MTS use in different regions of the Globe, including Antarctica, are presented. The best obtained processing results are demonstrated and discussed.
This study was partially supported by STCU grant 3165 and NSAU Contract No 1-02/03 (1274).
