时间域瞬变电磁法中心方式全程视电阻率的数值计算  

NUMERICAL CALCULATION OF ALL-TIME APPARENT RESISTIVITY FOR THE CENTRAL LOOP TRANSIENT ELECTROMAGNETIC METHOD

作　　者：白登海[1] Maxwell A Meju 卢健[3] 王立凤[1] 何兆海[1] 

机构地区：[1]中国地震局地质研究所,北京100029 [2]Department of Environmental Science,Lancaster University [3]大连理工大学电信学院,大连116023

出　　处：《地球物理学报》2003年第5期697-704,共8页Chinese Journal of Geophysics

基　　金：国家自然科学基金项目 (4 99740 17);英国皇家奖学金资助

摘　　要：给出了一种时间域瞬变电磁法视电阻率的数值计算方法 ,利用该方法可以容易地求出中心方式的全程视电阻率 .根据中心方式磁场垂直分量时间变化率 Bz T的核函数Y′(Z)的表现特征 ,以参数Z把整个瞬变过程分为早期阶段 (Z >1.6 )、早期到晚期的转折点 (Z =1.6 )和晚期阶段 (Z <1.6 ) .首先分别得到早期视电阻率和晚期视电阻率的精确值 ,然后通过转折点构成一条完整的全程视电阻率曲线 .虽然磁场垂直分量Bz 的核函数Y(Z)是参数Z的单值函数 ,但同样存在一个从早期到晚期的转折点Z =1.6 ,转换点两边仍然可以得到一条早期曲线和一条晚期曲线 .在数值计算中 ,当迭代步长ΔZ <0 .0 0 5Z时 ,视电阻率的相对误差小于 0 .5 % .理论模型和实际数据计算表明 ,与早期和晚期近似值比较 ,全程视电阻率具有更高的精度和分辨率 .A numerical method for calculating the exact all-time apparent resistivity for time domain transient electromagnetic method is proposed in this paper. According to the behaviours of the kernel function Y′(Z) for  B_z / T , the transient can be distinguished into early-time ( Z >1.6), transition point ( Z =1.6) and late-time ( Z <1.6) stages for a central loop configuration. First the exact early-time and late-time apparent resisitivities are calculated , then the exact all-time curve is founded by combining the two over the transition point. Although the kernel function Y(Z) for B_z is single valued, there is also a transition point Z =1.6 and the early-time and late-time curves can be obtained for Z >1.6 and Z ≤1.6, respectively. For the numerical calculation an iterative procedure is employed. The relative error in the all-time apparent resistivity will be less than 0.5 % when the variation of the parameter Z is defined as Δ Z <0.005 Z in the iteration. Model calculation and field data experiments show that the resulting all-time apparent resistivity can be easily defined with greater accuracy and higher resolution than that based on early-time and late-time asymptotic definitions.

关 键 词：瞬变电磁法 数值计算 中心方式迭代步长 全程视电阻率 

分 类 号：P631.2[天文地球—地质矿产勘探]