An Algorithm for Sea-Surface Wind Field Retrieval From GNSS-R Delay-Doppler Map
In this letter, a new method is presented to retrieve sea-surface wind fields by least squares (LS) fitting the 2-D simulated global navigation satellite system reflectometry (GNSS-R) delay-Doppler maps (DDMs) to the measured data. Unlike previous methods, all the DDM points with normalized power higher than a threshold are used in the LS fitting. To reduce the computational cost of the fitting process, a variable step-size iteration is employed. Three GNSS-R data sets that were collected at two different sea-surface regions by the UK-Disaster Monitoring Constellation satellite are used to validate the proposed approach. An 18-s incoherent correlation processing is applied to each data set to reduce the noise level, and ad hoc correction is made on the simulated antenna pattern. The retrieved wind results are compared with the in situ measurements provided by the National Data Buoy Center. The results show that an error of 1 m/s in the wind speed and 30° in the wind direction can be obtained with a lower threshold set as 30% to 42% of the peak DDM point.