aeromagnetic anomaly gradient method of extension and conversion

　　Title: aeromagnetic anomaly gradient method of extension and conversion
　　Author: Li Haixia
　　Degree-granting units: Zhejiang University
　　Keywords: aeromagnetic total field anomaly;; horizontal gradient;; vertical gradient;; extension;; frequency domain;; conversion surface
　　Abstract:
　　In order to meet the upcoming aeromagnetic gradient measurements, carried out this aerial magnetic gradient anomalies extension and conversion method. Aeromagnetic anomalies extension is commonly used in data processing methods, including plane upward continuation, flat and curved downward continuation extension. Plane extension is usually used to suppress or highlight the short-wavelength anomalies; surface extension method used to obtain data for Neodymium Magnets different interpretations, including song of the flat, level of music and song of the song. Gradient anomalies and aeromagnetic anomalies ΔT same extension also needs to deal with. One of the tasks of this paper is to study the gradient aeromagnetic anomalies for extension of fast, accurate and practical method.
　　Frequency domain fast Fourier transform (FFT) is the most commonly used aeromagnetic anomalies plane extension method. Upward continuation using FFT method is very stable, upward gradient abnormal extension of the plane still use this method. However, the FFT is very unstable downward continuation, magnetic anomalies on the next flight delay is usually not more than three times the pitch. Gradient anomaly compared with the total field anomaly usually contain more high frequency information, downward continuation method when the stability requirements are higher. Surface extension commonly used method is the equivalent source method and the Taylor series expansion, the main problems of these methods is to calculate the volume of work and the depth of downward continuation is limited, making the method very limited usefulness. This paper attempts to develop iterative methods for nearly two years, and interpolation - iterative gradient aeromagnetic anomalies transplanted to the plane downward continuation and extension of the surface. First, the use of model http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets data on the validity and accuracy have been tested, results showed that the iterative method for gradient data of the plane under the extension, and interpolation iterative method for gradient surface extension with high accuracy, to under extension of depth, and the results are stable. Through the noisy model data analysis of the results of random interference on the impact of extension, the results also proved that the iteration method and interpolation - iterative method has good stability.
　　The second part of this content is aeromagnetic total field and gradient components of the conversion, systems studied in the frequency domain conversion using the total field gradient, the total field and gradient conversion gradient between the conversion. Potential field in the frequency domain to convert has a simple expression to calculate the speed, etc., is often used to achieve conversion of the potential field method. However, conversion in the frequency domain to achieve the total field gradient and the gradient between the conversion, such conversion filtering operator frequency axis at the origin or existence of singularity, that is, the denominator is zero. This means that the conversion factor in the existence of the singularity of these frequencies can not be sampled, it can not be calculated using discrete Fourier transform on the conversion amount of the corresponding frequency spectrum values. We move like the introduction of the discrete Fourier transform, filtering operator function to solve the problem of existence of singularities, to achieve any total field and gradient convert any conversion between the two gradient components calculated. Verified by model method has high accuracy.
　　Convert the frequency domain method for the field on the plane, model test results show that when calculating the surface undulating, the use of the method of conversion will have a relatively large error. We combine the interpolated - iterative surface extension, converting the frequency domain method is extended to the total field and gradient on the surface of conversion, to achieve a surface gradient component aeromagnetic anomalies and rapid conversion.
　　We use the measured total field and gradient aeromagnetic data plane iterative downward continuation, and interpolation - iterative extension of the validity of the surface was examined. The results prove that the method has good stability and high accuracy; very fast method to ensure the practicality of the method. The measured total field and gradient of the conversion calculation, and convert the results compared with the measured data analysis, the conversion from the total field gradient, and gradient between the conversion results with the measured data are well consistent with the gradient , but the two groups compared to the results, the gradient between the results of conversion consistent with the measured data better; by the conversion of the total field gradient with the measured total field compared to a loss of some high-frequency information, but the overall pattern is also abnormal good relationship. In this case the results of the conversion of good consistency with the measured data to verify the validity of the conversion method, but also proves the reliability of the measurement parameters. The example calculations for the aeromagnetic anomaly gradient approach to extension and conversion applications provide some frame of reference.
　　Degree Year: 2009