Design Of The Semi-airborne Time-domain Transient Electromagnetic Receiving System

With the rapid development of China’s economy, the relationship between supply and demand of energy and resources becomes increasingly tense. In order to alleviate the contradiction between supply and demand which is becoming more and more serious, resource exploration should be actively carried out. As an effective detection method,the transient electromagnetic detection is widely used in oil, metal ores and other energy resources. In the transient electromagnetic detection, semi-airborne electromagnetic method is more convenient and efficient than ground electromagnetic detection, and compared with the airborne electromagnetic detection, it has a higher signal-to-noise ratio and better spatial resolution. These advantages make it widely used in detection of desert, mountains and other harsh environments and have a good prospect for development. This paper is to study the design of semi-airborne time-domain transient electromagnetic receiving system based on the glider.Based on the analysis of noise sources and components, this paper designs the low noise amplifier conditioning circuit based on the dual channel differential amplifier circuit: Using the low noise amplifier AD797 as conditioning circuit amplifier, the use of the dual channel differential circuit realizes a superposition of signal which can suppress white noise; using UAF42 as the core chip, this paper designs the 4th Butterworth low-pass filter to improve signal-to-noise ratio by filtering out high frequency interference. By analysis and comparison of synchronous mode commonly used in electrical instruments, this paper designs the high precision synchronization system based on GPS and FPGA which realizes not only the edge synchronization but also the absolute time synchronization. The measured signal acquisition uses USB-4432 data acquisition card, which is based on Σ-△ modulation and over sampling technology to achieve a 24 bit high precision acquisition.Based on the LabVIEW development environment, this paper adopts virtual instrument technology, uses a graphical language for the design of the PC software receiver system. In order to ensure the speed of data acquisition and storage, the TDMS file format is selected for data storage; the design of synchronous frequency setting module improves the flexibility of synchronization; the design of track display function module provides reference to the flight line; Design data extraction, superimposed average program, to achieve the data synchronization extraction and positive and negative polarity signal superimposed average, which suppresses the white noise, power frequency interference and conditioning circuit offset. In addition, according to the requirements of the operation of the system software, in order to improve the practicality of the software, this paper integrates and improves the relevant procedures.In order to verify the performance of the system, the conditioning circuit, GPS synchronization, and PC software were tested, and the results of the relevant experiments were analyzed. At the same time, the transient electromagnetic signal was measured in the laboratory condition, and the test results were analyzed to verify the feasibility of the system. At last, the work is summarized. In view of the deficiency of the system, this paper puts forward some suggestions for the next work.