Abstract
The collocated normalized radar backscattering cross-section measurements from the Global Precipitation Measurement (GPM) Ku-band precipitation radar (KuPR) and the winds from the moored buoys are used to study the effect of different sea-surface slope probability density functions (PDFs), including the Gaussian PDF, the Gram–Charlier PDF, and the Liu PDF, on the geometrical optics (GO) model predictions of the radar backscatter at low incidence angles (0 deg to 18 deg) at different sea states. First, the peakedness coefficient in the Liu distribution is determined using the collocations at the normal incidence angle, and the results indicate that the peakedness coefficient is a nonlinear function of the wind speed. Then, the performance of the modified Liu distribution, i.e., Liu distribution using the obtained peakedness coefficient estimate; the Gaussian distribution; and the Gram–Charlier distribution is analyzed. The results show that the GO model predictions with the modified Liu distribution agree best with the KuPR measurements, followed by the predictions with the Gaussian distribution, while the predictions with the Gram–Charlier distribution have larger differences as the total or the slick filtered, not the radar filtered, probability density is included in the distribution. The best-performing distribution changes with incidence angle and changes with wind speed.
Highlights
The radar backscatter from the ocean surface is closely related to the surface slope distribution, which is a statistic that can be used to quantitatively describe the ocean surface roughness
The predictions are compared with the Global Precipitation Measurement (GPM) Ku-band precipitation radar (KuPR) counterparts, and the comparison indicates that, when using the KuPR backscatter measurements as a reference, the predictions have a bias of 0.01 dB and a root mean square errors (RMSEs) of 0.98 dB for the normal incidence angle and a bias of −1.35 dB and a RMSE of 2.74 dB for all the incidence angles
Downloaded From: https://www.spiedigitallibrary.org/journals/Journal-of-Applied-Remote-Sensing on 08 Nov 2021 Terms of Use: https://www.spiedigitallibrary.org/terms-of-use predictions and the bigger errors at the larger incidence angles is probably due to the Bragg scattering component, which is not included in the geometrical optics (GO) model but becomes more important toward increasing incidence angles, while the bigger errors at lower wind speeds may be due to the effect of the constant presence of background swell on radar backscatter, which is much more obvious at weak winds.[13]
Summary
The radar backscatter from the ocean surface is closely related to the surface slope distribution, which is a statistic that can be used to quantitatively describe the ocean surface roughness. The Liu PDF is an improvement over the Gram–Charlier distribution It fits the Gram–Charlier distribution in the range of small slopes and works well in the full range of surface slopes.[4] the application of the Liu distribution is limited as the explicit expressions to determine the peakedness and skewness coefficients are not given in previous studies. The skewness can be ignored because of its very small order.[6] In this paper, a reasonable estimate of the peakedness coefficient in the Liu distribution is obtained using the Global Precipitation Measurement (GPM) Ku-band precipitation radar (KuPR) cross-section data and buoy wind speed data. Distribution, and the Gram–Charlier distribution in predicting the radar backscatter at low incidence angles at different sea states is analyzed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
