Research On Calculation Methods Of Apparent Resistivity Parameters For Controlled Source Audio-frequency Magnetotelluric

The CSAMT(Controlled Source Audio-frequency Magnetotelluric) method divides the survey area to the far, near and intermediate zone based on the wave number and the space between the transmitter and the receivers. We usually adopt the cagniard resistivity method processing data which is widely used in MT(Magnetotelluric). The cagniard resistivity method used on the far-zone field can include the vertical changes of the geoelectric section objectively. But when this method is used on the none far-zone it can produce great distortion, which will affect the further interpretation for the curve greatly. Even though, we have to observe the intermediate-zone field and even the near-zone field in practical work for the restraint of many kinds of subjective reasons. The electromagnetic field of the intermediate-zone is a complex function of the space between the transmitter and the receivers, frequencies and the geoelectrical parameters, which has substantial useful information. Therefore it makes a lot of practical significance to make reasonable use of the data collected from the intermediate-zone field. For that reason, many reseachers are persuing some definite correction methods and a new definition of resistivity to make better use of the data collected from the intermediate-zone field. So far, the reseaches that have been taken always have shortages more or less and there is no definite conclusion on the vertification of the processing results of the test data.I work on this paper with the purpose of finding out a definite definition of the full-zone resistivity based on the early achievements and realize the procedure of the data processing by program. And eventually improve the quality of data processing by making a systematically comparison between the results of data processing based on two definitions of resistivity. So I designed three models and took advantage of test data from one station, processing the data achieved from forward modeling and the test data based on two definitions of resistivity. Make a conclusion by comparing the results of those two kinds of methods. The results of the forward modeling data show that the full-zone resistivity method have the same outcome with the cagniard resistivity method when it is far-zone field. When it comes to none-far zone field, it can effectively remove the impact of the source and correct the distortion curve to a significant extent. Thus this method can objectivelly reflect the resistivity distribution underground. It is of great help to improve the quality of data processing and can increase the coverage of the useful data. The results of the test data show that it is completely workable using the full-zone resistivity method. This way of definition can improve the distortion curve to a significant extent and achieve the purpose of improve the quality of data processing.