An Application of Sq Variation Spatial Patterns on Diurnal Variation Correction in Marine Magnetic Survey

In the case of marine magnetic survey, especially in remote sea, it is hard to set a base-station (magnetometers in buoys or seabed) recording temporal variations of geomagnetic field simultaneously for diurnal variation correction. Available methods make numerical calculation, such as geographical interpolation and weighted average, by using simultaneous observations in land to get these inaccessible variations. However, as a result of ignoring the underlying physical mechanism, these numerical methods are always with substantial errors and limited applicable in sea area close to land. On the other hand, solar-quiet (Sq) daily variation, the main part of diurnal variation, is known to be generated by Sq current system in the E-region of ionosphere and has significant spatial patterns. On this basis, we collected massive geomagnetic data from geomagnetic observatories in China and got applicable patterns by analyzing Sq variations extracted from these data. The difference between the Sq variation curves of two stations in north and south side of Sq current respectively is Gaussian distributed over time. Taking this pattern into account, we choose Sq variation curve of the most south station as a base curve and fitted differences between curves of other stations and it by Gaussian functions. Then, an empirical model of latitude and longitude is obtained by regression analyzed coefficients of those Gaussian functions. After putting latitude and longitude of a position into this empirical model and adding the result curve to base curve, a Sq variation prediction of this position is achieved. The test result of this new method is much better than those numerical methods above: in the mid-low latitude, the prediction is effective in a much wider range of 20 degrees longitude and with remarkable lower errors.