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摘要
Large fixed loop is popularly used in time domain transient electromagnetic prospecing (TDEM/TEM) for areal deep soundings, which offers many major advantages especially for areas with large depth and density. Due to the inhomogeneity near the loop sides that is referred to as the side effect, data processing and interpretation is very difficult when the receiver deviates from the loop center. Particularly it would take a long time to calculate all-time TEM response and present algorithms are inefficient for such mass data. The article proposes a numerical algorithm which not only can decrease calculating time but also satisfy the required precision. According to the behaviors of the kernel function Y(Z) and Y'(Z) respectively for b(z) and partial derivative b(z)/partial derivative t, the transient field is divided into early-time (Z -> 0), middle-time and late-time (Z ->infinity) stages for a rectangular loop. In late- and early-time stages, asymptotic series for Y(Z) and Y'(Z) are used. For middle-time, the error function is calculated by rational Chebyshev approximations, and the fixed-integral relevant to radial distance is calculated by Romberg's rule integration. With this method Y(Z) and Y'(Z) can be calculated at any point except on the loop path. Model calculation shows that our method can speed up by at least four times with the relative error less than 0.0002% for both Y(Z) and Y'(Z). When the measure point is away from loop edges more than 25% of the loop size, required CPU time is only 1 second which is seven times as fast as the conventional method. For other measure points, CPU time is about 3 seconds which is four times faster.
- 出版日期2012-6
- 单位中国科学院地质与地球物理研究所兰州油气资源研究中心; 中国科学院地质与地球物理研究所; 中国科学院大学
