Signal processing techniques in ionosphere sounding and trace extraction from ionograms

The ionosphere plays an important role in high-frequency radio communication. An ionogram, as an effective way to get useful information of ionosphere, should be analyzed correctly and effectively. Unfortunately, the ionograms are generally distorted by background noise and strong signals interferences from other transmitters. In this paper, two techniques are proposed to obtain high-quality ionograms by reducing those interferences. The proposed techniques contain radio interference mitigation and modified mean filtering. These techniques have been well proved by data from ionosonde and perfect result could be seen from the comparison between the processed data and the unprocessed data. After getting the clearer ionograms, an algorithm is proposed for extracting main traces from the ionograms which is based on image recognition. Also, the performance of this algorithm is tested by data from ionosonde and the result is perfectly well. The test data were obtained from the ionosonde operating at Dulan. The proposed algorithms in this paper should be useful for further analysis of ionograms.