| Fixed-wing airborne transient electromagnetic method is a commonly used method of airborne geophysical exploration,which carries electromagnetic exploration equipment on fixed-wing airplane.Because of its large magnetic moment,stable flight attitude,long endurance and low exploration cost,it is widely used in exploration and geological mapping with large exploration depth,large area and small scale,and has a broad application prospect in mountainous areas,deserts,Gobi and other complex terrain areas,and provides fast,efficient and deep equipment and technical support for China's energy development strategy and land resources investigation.This paper relies on the key project of the National Key R&D Plan” Fixed-wing time domain aero-electromagnetic measurement technology system development”.In this paper,the principle and signal characteristics of Fixed-wing airborne transient electromagnetic method are analyzed,and the data acquisition technology of Fixed-wing airborne transient electromagnetic data based on virtual instrument is studied as follows.The cascade noise model of receiving coil and preamplifier is analyzed.According to the characteristics of transient electromagnetic signal,the differential amplifier circuit,which can effectively suppress common-mode interference and amplify transient electromagnetic signal,is designed by using low noise and low power consumption INA128 instrument amplifier.The corresponding low pass filter circuit and long line transmission circuit are designed to suppress the high frequency noise beyond the receiving bandwidth,and the signal is transmitted through the cable to the acquisition system by differential transmission to improve the anti-interference ability in the transmission process.The combined mode of DC-DC converter and LDO linear voltage regulator is used to design the power supply,which can suppress the corrugation of the power supply and maximize the performance of the system.The data acquisition is built on the PXIe platform,and the 24 bits high precision sampling is realized by using the mature PXIe-4492 dynamic signal acquisition card.The PXIe-6674 T clock is used to improve the precision of the system clock and generate the synchronous signal.The synchronization between the sampling clock and the transmitting synchronous signal clock is completed by software configuration.Data acquisition software is developed in LabVIEW environment.The whole software system is designed based on the “Producer-Consumer” framework,and the queue is used to transmit control messages and data.While ensuring the speed of data acquisition,the functions of data storage and processing are realized.The XML file is used to save the system configuration,to reduce the repeated configuration work.Choose TDMS file format and multi-file automatic storage way to store a large number of raw data.The noise characteristics of transient electromagnetic signal are analyzed,and the amplitude statistics of human noise in 50 Hz are carried out to judge the noise level in real time.The 50 Hz humanistic noise is removed by bipolar positive and inverse superposition,the sferic noise is removed by median filter,the coil motion noise is removed by one-dimensional interpolation method,the noise removal effect is good.Extract Off-time data for stack pumping,and then form profile display.Finally,the performance of each part of the system is tested and analyzed,which verifies the feasibility of the data acquisition system,and the performance of the system meets the requirements of airborne transient electromagnetic method,and puts forward some suggestions for the next step. |
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