Software Design Of Four-Channel Electromagnetics Receiver

The magnetotelluric sounding is a geophysical method for the earth exploration based on electromagnetic induction principle. This theory can analyse a variety of impedance using different frequencies to detect the resistance distribution at different depth underground. Because of its large-scale characteristic, strong resolving power, lower cost and portability and so on, this method is used widely in prospecting mine, especially for the oil. It can only get the information from deep layer because its source field is from natural field whose frequency is very low. If we use the natural electromagnetic wave and the electromagnetic wave sent by the transmitter as the source field, we can get the information not only from the deep layer but also from the shallow layer. With this idea, we designed the hybrid-source electromagnetic instrument. Now, this kind of instruments is all from import. It is important for our country to develop this kind of instrument with independent intellectual property rights. This thesis discusses especially the software design of the hybrid-source electromagnetic receiver.The thesis first expounds the theory of hybrid-source electromagnetics exploration, analyses domestic and international development actuality of the same type instrument. And the software design scheme of the portable receiver for fieldwork was given out. In the thesis, the realization and the result of every function module have been presented. Due to the virtual technology, we design the application software of the receiver. And the design period becomes shorter, and the cost is reduced. By signal analysis and signal processing, we analyse the magnetic sensor sensitivity and get the sensitivity curve in frequency domain. The software of data processing is given out after analyzing magnetotelluric theory. The test experiments have been made utilizing the simulative data and the data from eh-4 instrument. And the test result has been given out after the test.The thesis includes 6 chapters:Chapter 1 introduces the background and significance of researching task, summarizes domestic and international development actuality and design features of the same type instruments. This part proposes the main work of this thesis.Chapter 2 mostly introduces the basic knowledge of the magnetotelluric theory. The chapter firstly indicates the form of the natural field, and then puts forward the horizontal layered module. And consequently the definition of the apparent resistivity is educed. In this chapter, the theory of the scalar resistivity and the tensor resistivity has been introduced, and the theory of the scalar resistivity is emphasized particularly.Chapter 3 focuses on the software design. Analyzing the requirement of the instrument, the holistic scheme was brought forward. The instrument is developed by the virtual instrument platform LabVIEW. The application takes charge of parameter setting and transferring, real-time control, data transferring and display, data analysis, file management, etc. It has a beautiful front panel, and it is handled expediently.Chapter 4 discusses the method and process of the calibration for the magnetic sensor. Analyzing the significance and design principle of the sensor calibration, a calibration method using the squre wave was given. The sensor sensitivity was got according to the design parameter. The VIs provided by LabVIEW, such as Fast Fourier Transform, spectrum analysis and so on, are used for data processing. The LabVIEW also provides the interface to other programme language to make the functions which are compiled by other programme language (like C language) called by LabVIEW expediently. The tests are conducted respectively inside the magnetic shielding barrel of the shielded room, under the classroom with strong noise from power lines, and in Jingyue park of Changchun away from the noise from power lines. And they are compared with the result given by the designer. The result indicates that the sensitivity curve can satisfy the requirement of the sensor calibration in a range of frequency. But the method still needs to be improved to get more accurate result.Chapter 5 introduces hybrid-source electromagnetic data processing. The improved spectrum analysis method is used for data processing. The result shows that it is well achieved the targets. During the data processing, the top-quality points are chosen to be analysed in order to improve the result's precision. Finally, the data processing method is tested using the simulated data of the symmetrical half space model and power spectrum file provided by eh-4 instrument. The test results and the conclusion are given.Chapter 6 summarizes the work of the thesis. Some advices for the future work are brought forward after analyzing the disadvantages.