Data Acquisition And Real-time Processing Of Electromagnetic Survey Based On Pseudo Random Sequence

With the rapid development of current social economy, leading to the great consumption of various resources, especially the mineral resources, and the quick survey of mineral resources has also increased. Compared to other geophysical methods, electromagnetic survey has the advantage of low cost, high efficiency, adaptability and so on. It has the high value in the geophysical field. However, large-scale equipment is not suitable in China, because the complex geological features. New areas geological exploration such as project site decision, foundation monitoring, detection of metal pipes and underground cave detection raise high requirement to the instrument, include detection speed, accuracy and portability. Therefore, it has practical significance for develop real-time, high precision and portable electromagnetic detection equipment.Time domain or frequency domain electromagnetic exploration method is the traditional method, which has a low precision, weak anti-jamming capability and low efficiency. To improve the SNR and accuracy, often need to increase the power supply or increase the number of observations. In recent years, pseudo-random system identification method is widely used in the field of signal detection, for its simple generation, obviously random nature and suitable correlation properties. Pseudo-random sequence can limit the noise affection to a low level. It is used to do system detection in weak signal, and has an accurate identification result. The results of a cycle observation can obtain the traditional time domain and frequency domain result simultaneously.The content of this thesis focus on the design of electromagnetic detection system, and real-time data processing based on m-sequence. The thesis consists of three parts:In the first part, I have studied the theoretical knowledge of pseudo-random system correlation identification. Such as the basic principle of pseudo-random system correlation identification, the characteristics of m-sequence. I used MATLAB software to analysis the correlation function and spectrum specialties of m-sequence. The result showed the advantages of using m-sequence as the source signal in an electromagnetic field exploration system.In the second part, it introduces the design and implementation of the electromagnetic detection transmitter and receiver. The new transmitter has improved power driver module design, improved off effect though add an absorption circuit comparison with the old. Besides, the new transmitter achieved sending pseudo-random sequence. In order to meet the need of electromagnetic exploration, a high precision digital recorder mainly made by the high performance24bit A/D, two stage programmable amplification, filter and logic control core FPGA is introduced. The collected data send to PC via a high-speed data channel, which is built between FPGA and PC through applying the chip CY7C68013-A as the USB2.0interface chip. At the same time, touch screen is another choice to achieve human-computer interaction, Usb disk or SD card is available to store collected data.The third part is about research on real-time processing of the collected data. At first, we simulate and analyze m-sequence correlation calculation to achieve denoising and identify the impulse response of the system. Afterward, introduce the principle of m-sequence generation and FPGA realization. Finally, simulation analysis and realization of the synchronization overlapping average algorithm for denoising based on FPGA has been put forward, which combine with the correlation identification has greatly improve the accuracy of the pseudo-random exploration receiver to detect weak signals.The major goal of this thesis is to design a pseudo-random sequence electromagnetic detection system with high accuracy, real-time performance and portability, and finally achieve pre-research of the prototype and associated data processing methods. In order to verify the prototype performance indicators, each functional module has tested in the laboratory. In an addition, we have taken the transmitter and receiver to do a number of joint testing in the field. Test results show that:the prototype reaches the design requirements.