基于加权模型参数的归一化磁源强度三维反演

The 3D inversion of the normalized source strength data based on weighted model parameters

强剩磁的存在使磁化方向与地磁场方向偏差很大,进而对常规的磁异常反演和解释产生很大的影响。归一化磁源强度(normalized source strength,NSS)是一种弱敏感于磁化方向的转换量,它与场源的中心对应性比同类型的转换量要好。基于模型参数加权,采用共轭梯度的反演算法,使所有反演网格单元的综合灵敏度一致,以消除NSS核函数随距离的四次方衰减的影响。将这种改进的正则化共轭梯度算法应用于剩磁条件下的NSS反演。在研究区内存在剩磁情况下,与直接反演磁异常相比,NSS反演提供了更为可靠和稳定的解;与常规正则化反演方法相比,这种模型参数加权的方式能更好地降低NSS反演中核函数随距离的四次方衰减对反演结果的影响,且其反演结果能更好地刻画场源体的几何形态与物性分布。模型和实测数据测试结果证明了该剩磁条件下的反演方法的有效性和适用性。

The existence of strong remanent magnetization makes the large deviation between the total magnetization direction and the induced magnetization direction.Moreover it will have a great impact on the conventional magnetic anomaly inversion and interpretation.The normalized source strength （NSS） is a quantity which minimally affected by the direction of remanent magnetization.The NSS produces a higher level of centricity compared to the other transformations of the magnetic field that are used for the same purpose.In this paper,we use a conjugate gradient inversion algorithm based on weighted model parameters to make all inversion grid cells have the same integrated sensitivity,which can be used to eliminate the effects caused by the NSS forward operator decay with fourth power of distance.Under the effects of strong remanent magnetization,we applied the improved regularization conjugate gradient algorithm to invert the NSS data.The NSS inversion produces a more reliable and stable image of the subsurface magnetization distribution than using the observed magnetic field data directly.What＆#39;s more,compared with conventional 3D inversion,the weighted model parameters can better reduce the effects from the decay with fourth power of distance and the NSS inversion results can better depict the geometry and physical properties distribution of the source body.We verify the effectiveness and applicability of the inversion method presented in this paper for three dimensional magnetic susceptibility with synthetic and field data.