Study On Downward Continuation Algorithm For Magnetic Anomaly Gradient

For the advantage of all-weather,all terrain,high concealment,etc.,geomagnetic aided navigation system has become an integral part of inertial assisted navigation system.Underwater geomagnetic aided navigation and positioning system is based on the principle of underwater geomagnetic matching,and its positioning accuracy has a direct relationship with the precision of underwater geomagnetic database.Field continuation technique is an effective means to build underwater geomagnetic database.This paper researched magnetic anomaly gradient data which contained more geomagnetic information,and focused on the field downward continuation techniques in underwater magnetic anomaly gradient reference map construction with high-precision and high-efficiency.As the instability of field downward continuation,many scholars committed to pursuing a variety of algorithms to solve problems in this regard.Various improvements based on integral iterative algorithm not only effectively solve the problem of instability in the potential field downward continuation of large distances,but also raise the accuracy and speed of data processing has been greatly improved on the basis of ensuring a large distance downward continuation,.This paper introduces the elements of the geomagnetic field and its basic structure briefly,and brings out the research target of this paper-magnetic anomaly gradient after the introduction of total intensity magnetic anomalies.Besides,field continuation expression of magnetic anomaly gradient in spatial and frequency domains is derived,providing a theoretical basis for the study of the subsequent algorithms.Based on the analysis of the change of magnetic anomaly gradient extension factor,this paper points out that traditional fourier transform method for downward continuation process is unstable.Traditional frequency domain downward continuation iterative method is an iterative method based on Fourier transform,in order to reduce the amount of computation and improve the computing speed,it is required to use Fourier transform to convert the data in the spatial domain to the frequency domain before iteration.In this paper,for the purpose of improving the calculation speed,it is found that Hartley transform can ensure that entropy and energy are unchanged before and after transformation through the research,Hartley transformation eliminates the imaginary part of the Fourier transform operation as a real number domain transformation,as a result of which,the computing speed has improved a lot over the Fourier transform.In this paper,Hartley transform based iterative method for downward continuation by using Hartley transform instead of the Fourier transform.Finally,using simulation by application of theoretical models and the measured data to test the Fourier transform based iterative method for downward continuation and the Hartley transform based iterative method of downward continuation.The results show that Hartley transform based iterative method to ensure the accuracy of the downward continuation and can significantly reducing the computation time.Aiming to improving the shortage of noise-immunity using Hartley transform based iterative method,this paper researches the magnetic anomaly gradient downward continuation regularization algorithm combine Regularization Theory.At first this Paper introduces the classic Tikhonov regularization theory and some common regularization parameter selection method;Defines a downward continuation regularization operator by regularization;The operator can guarantee the results of downward continuation continuous depends on the observed data;Curvature function with the use of L-curve method to select the optimal regularization parameter;test and verify the Regularization algorithm by gradient magnetic anomaly data that added noise,the results showed that the downward continuation gradient magnetic anomaly regularization algorithm has stronger noise suppression and Shows good adaptability.Finally,the scope of application of the two algorithms is discussed.Finally,in order to meet the needs of the actual research,combing Matlab and VC + + s respective characteristics,a simple composition software that can be used in the laboratory study is designed by using a mixture of both programmatically.The software can load the data files,after entering the downward continuation depth and click the button corresponding algorithm,automatically draw the gradient magnetic anomaly contour map at the Billiton extended depth position.