Ionospheric diagnostics for skywave sea-state radar

Ionospheric motions and spatial multipath distort the sea-echo spectra obtained with HF skywave radars. At the SRI-WARF radar, two sweep-frequency ionospheric diagnostics are used on-line to help select frequencies and ranges most likely to be free of such distortion. They are a near-vertical-incidence ionogram and a ground-backscatter ionogram covering all paths within the radar beam. The authors have correlated the quality of radar spectra obtained over several days' operation with the location of the operating frequency on the two ionograms. The result is some tentative guidelines for choosing frequencies that give the sharpest spectra.