Region detection and statistical analysis of HF E, F layer ionospheric clutter RD spectra

Abstract

The echoes signal from ionospheric in High Frequency Surface Wave Radar (HFSWR) are the unwanted receiving signals propagating through ionosphere along different paths instead of sea surface, which is collectively called ionospheric clutter, affect most of the operation range beyond 100km. However, it brings the HFSWR another new function to survey the change of the ionosphere. Lots of observations show that ionospheric clutter badly affecting HFSWR is associated with the E layer and F layer [1]. Literatures proposed methods to suppress ionospheric clutter utilizing spatial discrimination [2,3], polarization filter [4], multiple carrier frequency operation [5], or auxiliary antenna [ 6 ], etc. In Space-Time Adaptive Processing (STAP) algorithms, the statistics of the ionospheric clutter usually can be got by training the data consisting of clutter during multiple scans. However, it's an omni-bearing mitigation operation in all the range bins of range-Doppler (RD) spectrum map because it's difficult to estimate the direction of ionospheric clutter in advance. It's obvious that good mitigation performance can be got in the region contaminated with the clutter, while targets can also be suppressed as clutter even in the RD map without ionospheric clutter. What's more, non-homogenous clutter in the training data including ship targets or other types of clutter can also affect the learning results.