On model identification for distortion correction of OTH radar signals

When HF skywave radars are employed for missions where high Doppler resolution is required, such as ship detection or remote sensing of the sea surface, nonstationarity of the ionospheric propagation channel within the coherent integration period often occurs to the extent that the Doppler spectrum is corrupted and the mission is unsuccessful. To overcome this problem, various signal processing techniques have been developed to maximise the detection probability and estimation accuracy. In the best-known methods, the nonstationarity is modelled as a smooth but nonlinear variation of the phase path, which is then estimated from one or more peaks in the power spectrum and removed by conjugate demodulation. We outline some extensions to the process of phase modulation distortion correction, based on a more elaborate model of the distortion process, to overcome some of the limitations of the previous approach