Study On Downward Continuation Algorithm For Magnetic Anomaly

Geomagnetic Aided Navigation (GAN) is an all weather, all-day, all terrain military navigation technique of high imperceptibility by using geomagnetic feature, and it has broad application foreground in high tech weapons such as underwater vehicles, cruise missile. The construction of geomagnetic database is a foundational technique in GAN. Downward continuation technique for potential field is an effective tool for geomagnetic database construction. Around the high precision and high efficiency requirements of GAN, this thesis is focused on the downward continuation technique for geomagnetic database construction. The performance of the proposed techniques and methods is preliminarily verified by real experiments.The main contents and contributions include the following aspects:(1) Based on a deep analysis of the characteristics of the geomagnetic field, the thesis introduces the composition and seven factors of the geomagnetic field briefly, as well as the differences between the geomagnetic anomaly data and geomagnetic anomaly field. After that, the thesis builds up geomagnetic downward continuation principle, which sets the basis for the study of geomagnetic downward continuation algorithms.(2) One-step downward continuation for geomagnetic anomaly data based on iteration method is researched. This thesis gives a full description to the iteration method in both space and wave number domain, and derives an equivalent one-step downward continuation wave number domain operator of this method according to the geometric progression trait of the iterative formula in wave number domain. We define a new iterative termination rule in wave number domain, and pre-estimate the number of iterations according to absolute difference between two iterations of the analytical expression. The one-step downward continuation method is tested on both model and real data. The results show that it yields the same good result with the iteration method but with much higher computation speed, which can reach the level of the traditional Fast Fourier Transform (FFT) continuation method.(3) Instability is the inherent limitation of downward continuation, including both one-step method and iteration method. Based on integral iteration idea and regularization theory, a regularization method is proposed for downward continuation of geomagnetic anomaly data. We also present an L-curve method for the selection of regularization parameter. The regularization method is tested on different Signal-to-Noise Ratio (SNR) model data. The results show that the new method is much more stable than the iteration method, especially in dealing with low SNR data. When the iteration method can't achieve the downward continuation result, the regularization method can also achieve a very good result.