U-filter's gaussianization function for interference background

By weakening the bigger and strengthening the smaller, gaussianization can enhance the gaussianity of samples and improve performance of subsequent correlation test. Firstly, an explicit definition on gaussianizing filter and a practical method to evaluate the filtering performance are given. Secondly, based on the probability density function and its derivate, one typical gaussianizing filters, so-called U-filter, are proposed and studied. Instances with lake trial data are illustrated. Finally, two applications, one in spectrum estimation and the other in Rao test, are discussed.