| With the further increase of the demand for marine resources exploration,the deep-sea geophysical exploration technology is developing rapidly.Marine magnetic survey,as an important means of Marine geophysical exploration,is still facing many problems in the application of ocean exploration.This paper focuses on the discussion and summary of the amplitude difference in the same latitude during the diurnal correction of Marine magnetic measurements in order to provide suggestion for the improvement of the diurnal correction method of marine magnetic measurements.The geomagnetic diurnal variation varies with time and latitude,the interference can be as high as tens or even hundreds of n T,which is the most important error in marine magnetic measurement.The result of its correction has an important influence on the accuracy of marine magnetic measurement.According to Specifications for marine surveys-part 8: Marine geological and geophysical surveys GB/T 12763.8-2007,during the marine magnetic survey,stations are usually set up in the land area with the same latitude as the offshore work area to observe the geomagnetic diurnal variation.And the geomagnetic diurnal variation observation data after processed from land station is used as a substitute for the actual geomagnetic diurnal variation of the offshore work area during the high-precision marine magnetic survey.That is to say,it is believed that the geomagnetic diurnal variation of the established land station is consistent with the amplitude of the geomagnetic diurnal variation in the offshore survey area after being processed.The principle of this method is mainly based on previous researches' cognition of the characteristics of geomagnetic diurnal variation and phase change law,i.e.the phase and amplitude of geomagnetic diurnal variation curve are often greatly affected by latitude changes,and are minimally affected by longitude.However,it is found in this paper that there are still some differences between the amplitude of the diurnal variation curve of the offshore work area and that of the land station even under the same latitude in the marine magnetic measurement(the measurement object is the total field strength of the geomagnetic field).If we ignore the effect of this phenomenon on diurnal variation correction,it will undoubtedly cause some interference to the accuracy of marine magnetic measurement.In order to actively understand and explore this phenomenon,and try to summarize the law of its amplitude variation,this paper collected available marine magnetic survey data and corresponding land station diurnal variation observation data in different years(time span: 2005-2018),different work areas(range: 16 n-36 n,112 e-122 e),and further screened out a plurality of measuring line segments that can represent geomagnetic diurnal variation in a certain period of time in the marine work area by using the principle of local extremum comparison method.After that,the IGRF field correction and gradient correction are carried out on these survey line segments,and compared with the geomagnetic diurnal variation of land stations.It is found that:(1)there is a certain amplitude difference between the geomagnetic diurnal variation curves of offshore work area and land stations in the short-period variation interval,especially when there are obvious disturbances such as hook disturbance and bay disturbance(hereinafter referred to as abnormal interval).(2)Through sorting out and analyzing the marine magnetic survey data in previous years,it can be found that there is a definite proportional relationship between the amplitudes in the interval where there is amplitude difference between the geomagnetic diurnal variation of the offshore work area and the terrestrial stations within a certain range.(3)This proportional relation changes with the change of latitude,and the ratio of the geomagnetic daily amplitude on land to the geomagnetic daily amplitude on sea in the abnormal interval is between0.5 and 0.85. |
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