GD-4 electromagnetic instrument is based on and refers to a technique in which electrical resistivity is determined by making measurements of electric and magnetic fields related to naturally occurring currents (“tellurics”, caused mostly by lightning strikes) flowing in the ground.
It has many characteristics like the random signal processing technology, embedded real-time operating system technology, large-scale field programmable logic array technology, 32 A/D high precision and high speed recording technology and the latest electronic technology, electromagnetic high frequency earth (HMT), It also can do survey like audio magnetotelluric (AMT) and magnetotelluric (MT or LMT).
Common applications for AMT and HSAMT (GD-4)
1.Minerals and ground water exploration to 1,500m depth.
2.Deep engineering site characterization.
Considerations and Limitations for AMT and HSAMT
1.Data quality for AMT and the low-frequency bands of HSAMT depend on the availability of natural field sources. Natural AMT signal availability depends on the season, time of day, and weather.
2.Contamination by 50 Hz or 60 Hz power sources such as power lines, industrial machinery, or urban settings negatively affect data quality.
Advantages of AMT and HSAMT over similar techniques
1.AMT acquisition is faster than traditional MT. Acquisition for low-frequency MT data requires up to 12 hours on a single station. Collection of high-frequency AMT data at 10 Hz and above can be done in less than 15 minutes.
2.HSAMT transmitter setup is much faster and easier. A traditional grounded dipole CSAMT transmitter can take several hours to set up. A dual-loop induction transmitter as a high-frequency source can be set up in less than 10 minutes.
3.HSAMT can resolve shallow targets. HSAMT up to 100 kHz can image targets as shallow as 5 meters. Traditional low-frequency MT cannot resolve targets in the upper 100m. AMT to 10 kHz can resolve targets as shallow as 20 meters in conductive earth.
4.AMT and HSAMT sensor setup is easier. Traditional low-frequency MT surveys require the magnetic sensors to be buried at least 20cm in the ground, which can take considerable time and may be impossible in frozen or otherwise hard ground. High-frequency AMT or HSAMT magnetic sensors can often be used unburied. MT electric sensors use non-polarizing porous pot electrodes which must be buried in moist ground. The AMT electrodes can be metal stakes that are simply hammered into the ground.
Techncial Specifiaction of GD-4 Electromagnetic geophysical equipment
Method：MT,AMT, CSAMT Controlled Source Audio MT
Number of Channels 2Magnetic，2Electric
ADC: 32bit, high (maximum sampling rate 192ksps);
Dynamic range: 160dB, instant 130dB@24kHz, 0dB;
Frequency range: DC to 92kHz;
Input range: 10 V PP @ 0dB;
Noise level: <5nV/√Hz@24kHz, 36 dB;
Input impedance: electrical channel >10MOhm, Magnetic channel >20kOhm;
Gain control: programmed 0dB, 12dB, 24dB, 36dB;
Synchronization accuracy: ±100ns;
Power consumption: <10W@12VDC;
Size: 26 x 17.3x 10.6 cm;
Waterproof rating: IP67.
Self-test content: instrument gain, dynamic range detection, acquisition box, magnetic sensor sensitivity calibration;
Operating system: embedded Linux;
Display: 6.5 inch industrial grade LCD;
LCD brightness: 1200cd/m2, daylight visible;
Storage capacity: 32G;
Data transmission: USB2.0&
Battery capacity: 12.6V 13.4Ah, can work continuously for 16 hours;
Power interface: External 12V battery or adapter works.
M100K magnetic sensor
1Hz to 100kHz
M10K magnetic sensor
0.1Hz to 10kHz
1.0-6.0kHz (dead band compensation)
No.of sweep frequency
Transmit input power
25 x 10cm 30x transmitter