Study On Enhancement Method Of Downward Continuation Performance Of Geomagnetic Field

Geomagnetic matching navigation has great potential in military field and can be widely combined with military applications.It has the advantages of not being affected by weather and environment,not radiating information to the outside world,concealment,and navigation error does not accumulate over time.It has a good development prospect and plays an extremely important role in the military field.Geomagnetic matching is inseparable from high-precision geomagnetic reference map,but usually the data needed to establish geomagnetic map is measured at a certain flight altitude.Geomagnetic field continuation can obtain geomagnetic reference map of different altitude planes,which is the key technology to construct high-precision and full-space geomagnetic reference map.Firstly,on the basis of geomagnetic field continuation theory,this paper comprehensively considers the influence of data noise,regional scope and the discomfort of downward continuation on the continuation result,and proposes an integrated downward continuation scheme of "denoising + boundary effect suppression + adaptive filtering iterative method".Based on the basic principle of geomagnetic field continuation,this paper analyzes the influencing factors of downward continuation,and then carries out the subsequent theoretical research and simulation experiment of data pretreatment method and downward continuation method.Then,based on the integrated downward continuation scheme,this paper studies the pre-processing method of denoising and suppressing the boundary effect,which reduces the error of the measured data and its influence on the subsequent processing method.According to the characteristics of multi-source and superposition of geomagnetic field data,the denoising mechanism of Gaussian filtering and truncated singular value is compared,and the simulation of different buried depth shows that the buried depth has great influence on the denoising effect of the two.Therefore,the segmentation denoising strategy based on buried depth estimation is proposed to effectively improve the applicability of denoising method.Aiming at the boundary effect caused by finite length truncation of geomagnetic field data,the influence of regional scope on the boundary effect was analyzed,and the boundary effect suppression method based on cosine extended edge was adopted.The simulation results show that the extended edge effectively weakens the influence of the boundary effect on subsequent extension processing,and reduces the relative error of extension by12%.Finally,by analyzing the influence of buried depth on the continuation results,this paper introduces the adaptive filtering theory and combines the iterative method of geomagnetic field downward continuation,and proposes a geomagnetic field downward iteration method based on the adaptive filtering,which effectively improves the performance of downward continuation.Based on the mapping function of the downward continuation iterative method of geomagnetic field,an adaptive filter operator is designed to correct the residual term and suppress the high-frequency noise.The frequency band distribution of geomagnetic data is analyzed by means of average radial power spectrum and the regularization parameters of adaptive filter operator are determined.Simulation and experimental results show that the adaptive filtering iterative method has fast convergence speed and high stability under different burial depth models,especially in shallow source model,the continuation accuracy is 60% higher than that of Landweber method and ISVD method.