Spectrum Feature Extraction Of Marine Magnetic Noise In Marine Vector Magnetic Survey Data

The vast ocean contains rich resources and has become the focus of various countries’ development,and the development of marine exploration technology is of great significance to the maintenance of national maritime sovereignty.Obtaining resources and developing marine exploration technology are of great significance to the maintenance of national marine sovereignty.Therefore,understanding and developing the ocean has always been a topic of concern for scholars at home and abroad.As one of the important means of ocean exploration,marine magnetic survey technology has played a great role in the survey of seabed mineral resources and the exploration of seabed geological structure.With the development of science and technology,marine magnetic survey has been continuously extended from sea surface,shallow sea to deep sea,and the measurement technology has also developed from scalar measurement to vector measurement.Today,high-precision marine geophysical field measurement is the cutting-edge technology of national development.Studying marine noise in high-precision marine magnetic survey can be used as the most direct information to retrieve the characteristics of marine activities.The extracted noise analysis results can not only improve the quality of vector magnetic survey data,provide technical support for the subsequent research and development of marine magnetic survey instruments,but also provide technical support for the exploration and development of the ocean Safeguard national maritime sovereignty.We takes the extraction of marine magnetic noise spectrum characteristics as the research object,combines time-frequency analysis method with the research of marine magnetic noise signal,and based on the data collected by the same instrument at the Zhaoqing Geomagnetic Station in Guangdong Province,explores a marine magnetic noise acoustic stripping algorithm suitable for marine vector magnetic survey data,and uses this algorithm to process the vector magnetic survey data collected in the deep sea near the Qi’ao Island in Guangdong Province for a long time,The marine magnetic noise is stripped out,the spectrum characteristics are extracted and analyzed,and a simple mathematical model of marine magnetic noise is preliminarily constructed.The main contents of this paper are as follows:(1)The algorithm of marine magnetic noise stripping is studied.Using the land-based data collected at Zhaoqing geomagnetic station by the same instrument for deep-sea survey as samples,the magnetic survey data are preprocessed including peak removal,offset removal,temperature drift correction and Newton interpolation,to obtain the daily variation curve of Earth’s magnetic field with high signal to noise ratio,which is taken as the target data sample,and Gaussian white noise is added to simulate the marine magnetic noise to obtain the daily variation curve with noise.Improve the traditional wavelet algorithm by introducing the heuristic STEIN unbiased likelihood estimation principle to obtain the entire threshold of high-frequency wavelet coefficients.Compared with traditional wavelet algorithms,the improved wavelet threshold denoising can maximize the preservation of the lost signal information in high-frequency wavelet coefficients.After quantitative analysis and effectiveness evaluation,the percentage root mean square deviation and Mean squared error of the improved wavelet threshold denoising method are reduced by about 10% and 20% respectively,and the signal recovery effect is stronger.Explored an ocean magnetic noise removal algorithm suitable for ocean vector magnetic survey data,with an improved wavelet threshold denoising algorithm as the core.(2)Extract the spectrum characteristics of marine magnetic noise.Long period ocean vector magnetic survey data is very valuable,and research on ocean magnetic noise is even more scarce.The noise spectrum features extracted in this article can provide support for subsequent research.By analyzing the noise characteristics,the known noise source can be located through the frequency band,and the specific impact of the noise on the instrument records can be seen through the intensity.The Mathematical physics model can be constructed through analysis and processing,so as to improve the accuracy of subsequent instruments in collecting Earth’s magnetic field daily variation data and improve the reliability of the instrument work.Then,using the determined ocean magnetic noise stripping algorithm,the 18 day magnetic daily variation vector measurement data of 3800 meters in the offshore and deep sea of Qi’ao Island were stripped of noise,and the Periodogram method in the short-time Fourier transform and power spectrum estimation was used to extract the spectral characteristics of ocean magnetic noise.It was found that the ocean magnetic noise was mainly distributed in the H component,occasionally in the Z component,relatively less in the D component,and the frequency band was below 0.5Hz,The conclusion is that the strength is below 0.4n T.(3)A simple mathematical model of marine magnetic noise is proposed.Combined with the magnetic field interference in the ocean and the deep sea environment in the offshore area of Qiao Island,it is proposed that the main sources of the three-component noise are approximately the ocean currents,the ocean internal waves and the induced magnetic field generated by the seabed geological activities.According to the projection of the magnetic field on the three-component,a simple mathematical model of the ocean magnetic noise is preliminarily proposed.