基于最小梯度结构的2.5维CSAMT场分量灵敏度控制正则化聚焦反演

Like magnetotelluric, the topographic and small abnormal body below the surface must be consider when using the controlled source audio magnetotelluric method. There are the transition zone, non-dipole effect, the shadow and overprint effect of the field which introduced to CSAMT. Processing techniques of these problems are caused distortion of the data or to increase additional data observation. The studies proposed a novel processing approach, the forward problem consider the length of source and topography and the inversion use the electromagnetic field component. It will be high-precision CSAMT data interpretation scheme. There are obvious advantages using field components than apparent resistivity (or impedance). Apparent resistivity calculation is easy to cause the accumulation of measurement error, The result of inversion would not distribute by static effect when using magnetic field component, the sensitivity is easy to calculate when using field component, and it has full domain characters, through the combination of electric and magnetic field is expected to achieve the direct inversion caused by the static effects. The minimum gradient structure supported focus information was used in Inversion, the focusing factor was automatically adjusted about the sensitivity matrix, achieve the optimal model based on the ability to data distinguish，and improve the inversion model at transition zone.

可控源音频大地电磁法（CSAMT）与大地电磁法（MT）一样存在地形影响与静态效应，由于人工场源的引入，又出现了过渡带、场源的阴影效应与复印效应、场源的非偶极效应等问题。目前，对于这些问题的处理技术均以对数据造成畸变或增加额外数据采集为代价。本项研究提出考虑供电源长度的带地形正演和直接反演电磁场分量的反演，从全新的角度考虑上述问题，探寻提高CSAMT资料解释精度的新途径。反演直接以电场、磁场分量作为参数与采用卡尼亚电阻率（或阻抗）相比具有明显的优势：卡尼亚电阻率采用比值计算，容易造成测量误差积累；直接反演磁场分量不受静态效应影响；分量反演的灵敏度矩阵易于计算，具有全区特性；通过电场、磁场多分量组合有望实现引起静态效应异常体的直接反演。采用基于模型最小梯度结构支持的聚焦正则化信息，引入基于灵敏度矩阵信息的聚焦因子自动调整算法，可以实现基于数据分辨能力的最优模型反演，改善过渡带反演效果。

研究工作对可控源电磁法电磁场单分量2.5维正反演进行了深入研究。采用灵敏度信息定量研究可控源电磁法的勘探深度、分辨率，分析电场与磁场分量的勘探能力；模型灵敏度矩阵在“深度-频率”坐标下等值线的直线段斜率反应了数据的垂向分辨率，斜率越小垂向分辨率越好，最大勘探深度只与收发距有关。项目对比研究了电场、磁场分量反演与阻抗反演能力，表明可控源大地电磁的电场与磁场分量均具有测深能力。研究过程中分别采用总场算法与二次场算法进行2.5维正演，探讨了可控源大地电磁的静态效应与地形影响；引用稳定因子统一表示，通过伴随方程法求解电场与磁场分量的灵敏度矩阵，采用修正的“L-Curve”方法求解正则化因子，实现了2.5维可控源正则化反演。电场与磁场单分量反演有利于提高可控源音频大地电磁的反演精度，改善静态效应、过渡带反演效果。