The Study Of GEM-2 Data Processing And Inversion Methods For Sea-ice Thickness Detection

GEM-2 is a portable and efficient multi-frequency electromagnetic exploration system with broad applications in mineral exploration,engineering investigation,water resources survey,archaeological prospection,and agricultural soil assessment.With its increasingly deep and extensive applications,there are prblems of detection precision and efficiency of data processing despite the high data collection efficiency,especially in the detection of sea-ice thickness.This article has carried on some basic research and refinement to the data processing and inversion methods of GEM-2,which has been effectively applied to the GEM-2 detection of sea-ice thickness.In the data processing we do the following work to improve the data quality and processing efficiency:(1)Correct the system calibration error of sea ice GEM-2 data by three parameters included a gain factor,a phase,and bias term according to the widely used approach presented by Deszcz-Pan et al.after the drift correction.As was expected,the inverse sea-ice thickness matchs well with the drilling results.(2)Proceeding from the apparent conductivity conversion method of analogous GEM-2 electromagnetic systems and basing on the expression of the relative magnetic anomaly for a frequency-domain magnetic dipole in homogeneous half-space under quasi-static conditions,we derive higher-order approximate formulas of the apparent conductivity.At the same time,it is found that there is a translational and expansionary characteristic between the response curve of the relative magnetic anomaly and underground conductivity,and observation frequency.Accordingly,we propose a translation algorithm that can directly calculate the apparent conductivity.Through model test and field data processing results of GEM-2 sea-ice data,the effectiveness of this method is well validated.In comparison with the conventional and the higher-order approximate calculation methods of the apparent conductivity,this method features fast computation speed,high accuracy,and insensitivity to the instrument height.Meanwhile,it also helps explain the buried depth of the conductive layer,which provides a new method for calculating sea-ice thickness of multi-frequency electromagnetic detection of sea ice.As for the data inversion,by establishing a model space to realize the optimal selection of initial model before the conventional local linear optimization inversion,we present the fishing inversion algorithm which is suitable for the point-by-point multi-frequency electromagnetic inversion of layered media such as sea ice with little change in physical parameters of adjacent points.The algorithm amis at the high accuracy and real-time of inversion,and achieves good application effects in the GEM-2 data inversion of fourth Arctic sea-ice thickness.