Advanced Geophysical Operations and Services Inc. (AGCOS) participated in the 7th All-Russian EM Induction of the Earth Seminar and Workshop in the name of M.N. Berdichevsky and L.L. Vanyan which was held in Irkutsk, Russia from September 14 to 19, 2015. AGCOS presented the following papers:
Appearance at the turn of the century of the 5th generation multifunction electroprospecting instruments has made significant contribution to the development of electroprospecting techniques. New properties of the equipment include – light weight, compact, low power consumption, simple operation, high accuracy of the recorded parameters. One of the defining features is the application of 24-bit ADC. Technological advancements in the microprocessor development and computer technology allowed significantly improving hardware capabilities of the 5th generation instruments, i.e. going to 5+. Super multifunction 4 and 8 channel receivers can be used in both autonomous and manual modes (operator control). Receivers have intuitive user interface implemented on touch-screen display and several communication modes with a PC, touchpads, and smartphone. Instruments have flexible configuration of electric and magnetic channels (channels are interchangeable), which allows to use same receiver for such seemingly incompatible methods – Electrical Profiling, IP, Electrotomography, TDEM, MT and MVP. Application of wideband high frequency ADCs and corresponding processors can significantly improve the frequency range of field investigations, as well as noise filtering capabilities. Data acquisition systems are equipped with a wideband electric and magnetic components EM field sensors, as well as a wideband portable transmitter.
Magnetovariational profiling method (MVP) was introduced into the field practice in the 1950-60s of the last century subsequent to the works of Parkinson, Wiese and Schmucker . At that time, low frequency variant (10-1000sec frequency range) was widely used for the detection and parameter estimation of large electrical conductivity anomalies in the Earth’s crust and upper mantle. The appearance of the 5th generation of electroprospecting equipment in the 1970-80s allowed MVP method to become regular add-on to magnetotelluric soundings (MT) in the 5-component variant. At the turn of the century, active implementation into field survey practice of the 5th generation digital multifunction EM instruments  resulted in significant increase to the number of carried out AMT measurements, which were widely used for mining exploration. In turn, emphasized was the demand for the induction vector and tipper interpretation techniques. Besides the development of effective 2-D inversions, proposed were express interpretation methods [1, 2, 4] which allowed to estimate the parameters (depth, conductivity, angle of inclination, etc.) of the conductive body during the course of the field survey. Consequently, as well as due to the application of precision field tripods for quick and accurate installation of the magnetic sensors, the 3-component MVP method became an effective independent ground electroprospecting technique for solving wide range of mining exploration tasks.
Seabed EM surveys in shallow water environments have a number of specific particularities. Specifically, there is difficulty with hermetical sealing of EM instruments and the necessity of overcoming electromagnetic noise caused by underwater currents and sea surface disturbances. Another problem is the inability to employ large ocean going vessels in many areas, while the use of small vessels increases the demands on the size and weight of the equipment. There are also certain positive aspects in this, pertaining to the ability to use reliable acoustic communication between the marine EM instrument positioned on the seabed and the sea surface, as well as the use of beacons for identifying the location of the bottom apparatus. In this paper, discussed is a shallow marine EM data acquisition equipment complex that allows efficient use of standard ground EM instruments for carrying out investigations at a sea depth interval of 0-200m. This complex consists of 2x – 4x – 5-channel marine EM systems.
Application of the Frequency Domain Electromagnetic Soundings Method (FDEMS) for Geological Mapping and Mining Exploration
The electromagnetic (EM) methods in the frequency domain (FDEM) have become increasingly popular in the past decade due to their high resolution and sensitivity, as well as high immunity to EM noise. They could be separated in two groups:
- Shallow FDEM profiling techniques which use high frequency bands and mainly utilize only the magnetic components of the EM field;
- Electromagnetic soundings in wide depths intervals, consisting of two sub methods: the impedance soundings (CSAMT); and the individual components EM soundings (FDEMS). The last sub method combines geometric and induction soundings techniques.
Both electromagnetic soundings sub methods actively use magnetic and electrical EM field components and, whereas in the CSAMT only the far zone of the control source is being used, the FDEMS engages all three control source zones: nearest, middle and far. Such feature provides a number of significant advantages during field data interpretation. At the present time, hardware capabilities of recently developed wideband (50 000 – 0.0001 Hz) multifunction EM data acquisition systems allow to take full advantage from the application of the high resolution FDEMS method for solving a variety geological engineering and groundwater exploration tasks.