Methods for Extracting Backscatter Ionogram Leading Edges

Algorithms for automatic backscatter ionogram scaling are established. The algorithms are used in the backscatter sounding system developed by China Research Institute of Radiowave Propagation (CRIRP) and show good results. The autoscaling system has been developed in two overall stages. The first stage is the automatic cleaning of a raw ionogram, which filters the raw ionogram to remove the interferences and noises. The second stage is to extract features from the clean ionogram, such as the propagation modes, the leading edges, etc., and this paper describes part of this work. Methods for extracting backscatter ionogram leading edges are presented. For a single layer or the lower one of two layers, the leading edge is extracted by edge identification algorithm on the ionogram with interferences and noises removed. For the upper one of two layers, the leading edge is extracted by power and gradient algorithm based on Gaussian-fashion weights on the ionogram just after interference suppression. The methods given in this paper have high accuracy and are easy to implement. They are applied successfully in several projects.