Validation of Wind Speeds From Brown-Peaky Retracker in the Gulf of Mexico and East Coast of North America

Abstract

The performance of Brown-Peaky (BP) retracker on retrieving the backscatter coefficients, and then wind speeds, in coastal zones has been examined in this article. Eight years of Jason-2 waveforms are reprocessed by the BP retracker. An empirical wind speed model is used to obtain the altimeter wind speeds based on the BP-derived backscatter coefficients. The validation of BP-derived wind speeds is conducted through comparisons with wind speeds from the in situ anemometer and Jason-2 official altimeter product. The along-track root mean square errors (RMSEs) and biases between altimeter and anemometer wind speed time series are calculated pointwise to evaluate the data quality. The orthogonal regression analysis is computed to evaluate the overall data quality. The validation results show that the BP-derived backscatter coefficients are highly correlated with the square of the off-nadir angles. By removing this correlation-induced error, the quality of BP-derived backscatter coefficients is comparable to that obtained from the three-parameter maximum likelihood estimator (MLE3). The improved backscatter coefficients are beneficial for retrieving reliable along-track wind speed observations, which allows for lower and smoother RMSEs and biases. The 1- and 2-Hz BP-derived wind speeds achieve similar performance, implying that the application of high rate altimeter wind speeds in coastal zones is possible. We also find that the altimeter wind speeds are significantly dependent on the sea state in the last 20-km distance to the coast, where the bias between altimeter and anemometer wind speeds increases remarkably and varies inversely with the offshore distance.