Estimating Scattering Patch Area for a Direction Finding HF Radar

Abstract

We use the radar equation along with in situ observations of Bragg-resonant ocean waves to estimate the scattering patch area for each radial velocity observation from a direction finding high frequency (HF) radar operating at 13 Mhz. Estimated areas for range cells 2–10 (3–15 km) vary from less than 1 km $^{2}$ to more than 10 km $^{2}$ , with a mean of 2.5 km $^{2}$ and standard deviation of 2.3 km $^{2}$ . Assuming a 1.8 km effective range cell width, and given the known ranges, these are approximately equivalent to a mean angular width of 8.5 $^\text{o}$ , and a standard deviation of 10.0 $^{\circ }$ . The scattering patch areas follow a Weibull distribution, with scale and shape parameters 2.5 and 1.2. Patch area uncertainties, expressed as a percentage of the patch area, average 36%, with most below 50%. Knowledge of the scattering patch area could allow improved data combining methods (e.g., appropriate weighting or variable resolution totals), and improve the ability of HF radar networks to resolve small scale flows and eddies. Understanding the scattering patch size may also contribute to improved HF radar-based observations of coastal winds, as it plays a role in the relationship between wind speed and backscattered power.