大地電磁法為非破壞性的被動源地球物理探勘方法，主要利用記錄設站地點的自然電場與自然磁場的變化，加以運算得到視電阻率與相位曲線，供分析了解當地的地下電性結構。目前商業用大地電磁儀種類繁多，但由於規格制式化，加上儀器單價昂貴，因此在資源有限的情形下，限制了施測的彈性與效率。一般批次的收集資料，也難以進行良好的電磁場除噪校正，因此在雜訊的消除上也有較大的限制。為解決上述問題，本研究開發的同時序多頻道大地電磁儀系統SMMS (Synchronized Multichannel Magnetotelluric System)，為組合以多頻道可衛星正時高取樣率訊號記錄器、三軸通量閘磁力計與非極化電極所組成的系統。我們於台灣台中地區與宜蘭地區與商用大地電磁儀系統進行聯合測量並進行比較，確定兩者所收取之原始電磁訊號具有一致性，並驗證訊號的正確性。我們選擇在宜蘭清水地區與台中大坑地區架設數個同時序大地電磁測站，進行SMMS系統的儀器測試與訊號蒐集，並以自行開發之運算程式MMPC ( Matlab-based Magnetotelluric Preprocessing code)進行資料蒐集後的資料演算。在訊號的處理中，我們使用陷波濾波濾除電力線干擾，再利用互功率頻譜運算，來提高訊號間的相關性。並經過parzen window處理計算特定頻譜功率，最後用robust fit算出最佳的視電阻率值。最後比較商用儀器訊號與其處理程式的運算結果，我們初步驗證這套自行開發之大地電磁量測系統與後處理程式的有效性與正確性。未來將實地運用這套儀器來調查台灣地區的地層電性結構。;Magnetotelluric method is a non-destructive geophysical prospecting method of passive source. The station will record the changes of natural electric and magnetic fields to calculate the impedance tensors and apparent resistivity curves for understanding the local underground electrical structure. The market of commercial magnetotelluric instruments are with various kinds, but because the mode of standardization, and Price expensive. So in the case of limited resources, often limit the flexibility and efficiency of the construction survey. The present study was used development the synchronized multichannel magnetotelluric system. The self-developed instrument is the multi-channel system combined with satellite synchronized, high sampling rate record, one three-axis fluxgate magnetometer and the non-polarized electrodes. In the Taichung and Ilan area, we used commercial magnetotelluric measuring instruments and self-developed systems jointly determining the consistency and correctness. We set up several simultaneous sequence magnetotelluric station in Taichung Da-Keng region with self-developed magnetotelluric instrument at the same time for testing the equipment and signal collection, and the self-developed calculation program was applied to process the collected data. In our data processing, we use a notch filter to filter out the power line interference, and employ the cross power spectrum operation, to improve the correlation between signals, and the parzen window computing the specific frequency spectrum, and then calculate the apparent resistivity values with robust fit. We verified the processing program effectiveness and accuracy in magnetotelluric measuring system. We will use this magnetotelluric system in future to investigate the of Taiwan′s Geoelectrical section.
