Non-linear effects in HF radar backscatter from the ocean

Explores the limitations in moderate to high sea-states of the mathematical theory underpinning wave measurement with HF radar using data from the OSCR (Ocean Surface Current Radar) radar system. The fact that there are limitations has been known for many years but there has been little study of the nature of the limitations and of the quantitative effect on wave measurement. Preliminary results confirming extrapolations from results at lower radio frequencies to the upper HF band are presented. Of particular importance is the evidence of a strong directionality in the non-linearities which support the conclusion of earlier work that wave measurement may be possible in higher sea-states than the linearised theory would suggest