A Study On Measuring Technology Of Fix-wing Frequency Domain Airborne Electromagnetic System

HDY401 system, a tri-frequency fix-wing airborne EM system (FAEM system), is the only one with independent intellectual property at present in our country and has been applied successfully in the geophysical survey. In order to improve the quality of measurement data to satisfy requirements of large-scale production on stability and reliability, this paper studied systematically the measurement techniques of FAEM system, including optimization design of the receiver/transmitters coils, detection of weak signal in secondary field, the transmitter system of constant-current with high magnetic moment, digitization of the compensation system and auto-compensation for the primary field. Through employment of these new techniques, a new FAEM system, named HDY402, has been developed. A series of tests were carried out to compare the performance and effectiveness of the new system with the original one.The achievements made through the study are as following:Technology of the receiver/transmitters coils in aviation electromagnetism has been improved. The optimization design methods were established based on the estimation or calculation of the coils' self-inductance, mutual inductance, eddy current loss and distributed capacitance. A new receiver coil's shielding technique was also developed to enhance frequency selection quality and stability of coils.Based on synchronization filter, active filter and phase-sensitive detector, a new type of lock-in amplifier (LIA) was developed for avionic receiving system. By improvements of ultra-narrow bandwidth in receiving system, receiver's overload level and dynamic reserve have been increased, which is helpful to solve problems caused by overload distortion.The transmitter technology of constant-current with high power was first proposed and realized. On the basis of development of high-power DC-DC boost converter and digital sine wave oscillator with power cascading and transient protection, the transmitter system of constant-current based on PID control was developed, improving the anti-interference ability and sensitivity stability of avionics systems. The primary field auto-compensation method was realized for the first time in the HDY402 system. The digital compensation system based on real-time control of MCU and primary field auto-compensation technique based on fuzzy control have been developed, achieving a wide range precise compensation for the primary field, which is helpful to increase production efficiency and data quality.Combining the techniques described above, a new model of tri-frequency FAEM system was developed, improving measurement techniques for the FAEM system and filling technical gaps in primary field auto-compensation and constant current transmitter. Automatic measuring has been implemented owing to improvements in digitalization and intellectualization of the system.Performance testing results showed that the system's total magnetic moment and noise level are better than those of the AEM-05 system developed by the Finland and the United Kingdom, with significant progress in zero drift and sensitivity level compared with the former system. System stability and reliability have been verified in the airborne geophysical survey covering 80,000km within 2 years.Main technical specifications of the new system have been promoted, reaching or exceeding the level of the same type system abroad. Research results of this paper have established instrumental and technical foundation for the large scale airborne geophysical surveying.