| For the exploration of underground resources and spatial structure,conventional geophysical exploration technology is difficult to carry out rapidly on a global scale,but the rapid and uniform space-time coverage characteristics of satellites make it have great potential as a new carrier for geophysical exploration.At present,electromagnetic data of satellites are mainly used to study large-scale deep earth structure,but there are no feasible studies on near-surface detection at depths of 100 metres.Due to the low frequency of electromagnetic waves excited by magnetospheric sources,ionospheres and tides,raditional satellites electromagnetic detection can not detect shallow hidden objects.Therefore,the development of a VLF electromagnetic detection system with lightning as the excitation source and satellites as the carrying platform is of great value to the exploration and research of underground resources and structures.The VLF electromagnetic detection prototype based on the space-based platform developed in this paper includes two parts: the front-end of the system and the backend of the system.The front-end of the system is composed of inductive magnetic sensor and antenna conditioning circuit,and the influence of each parameter on the performance of the magnetic sensor is studied by analyzing the relevant physical parameters such as core material,size and winding specification of the inductive magnetic sensor,and its optimal design scheme is determined.The signal conditioning circuitry includes band-pass filtering circuitry with a pass band of40 k Hz-80 k Hz and a low-noise amplification circuit with an in-band gain of up to80 d B.The back-end acquisition system uses the ZYNQ-7020 core board as the main control board,DDR as the program and data storage space,and the synchronous 8-channel 16-bit AD7606 as the analog-to-digital conversion chip.The logic programming and clock management of each functional module are completed on the FPGA side of ZYNQ,and the functions of collecting,packaging and caching multiple data are realized,and the transmission and storage functions of raw data are realized on the ARM side.The test results show that the sensor has a sensitivity of up to 0.1m V/n T,an ADC signal-to-noise ratio of 81.826 d B,and an effective number of 13 bits,System linearity less than 0.4%,which basically meets the design requirements. |
