Measurement of wind speed and direction using multifrequency HF radar

HF radar has become an important tool for mapping surface currents in the coastal ocean. It is well known that HF radars are capable of measuring wind direction by using the relative strength of the echoes from the approaching and receding ocean waves at the Bragg resonant wavelengths. Here we examine the ability of multifrequency HF radar to measure wind speed as well as direction. In this study we use data collected over Monterey Bay, California in the late summer of 2000. At that time there were two buoys in the radar´s observational area that were capable of measuring wind speed and direction one near the Bay mouth and one nearer the shore. We investigate the relationship between the wind speed and the near surface currents and Bragg line ratios as measured by two multifrequency HF radars near Santa Cruz and Moss Landing, California. These radars operated at 4.8, 6.8, 13.4 and 21.8 MHz, measuring currents at effective depths of 2.5, 1.8, 0.9 and 0.6 m respectively. The method of partial least squares is used with results for speed of a standard error of prediction (SEP) of ≈ 1m/s, a bias of ≈ 0.5 m/s and an R² of ≈ 0.8. For direction the SEP ≈ 40°, the bias ≈ 4° and R² of ≈ 0.45. These preliminary results suggest that wind speed as well as direction can be estimated from multifrequency HF radar data.