Research On Airborne Spectrometer Wave Spectrum Inversion Method

As a new remote sensors dedicated to detect waves,wave spectrometer can effectively solve many problems of SAR inversion wave spectrum,while its simple modulation function,small azimuth truncation effect,no additional input data and other advantages,the wave spectrometer has become an important method of remote sensing to detect the waves.This article is based on Beijing Research Institute of Telemetry BRIT airborne wave spectrometer and the French CNES STORM airborne wave spectrometer several flight test data,compares similarities and differences in the data processing in order to provide reference for the future development of domestic spectrometer;analyzes the wave backscattering characteristics,including wave backscattering coefficient anisotropy and asymmetry of the small and medium incidence angle and wave spectrum azimuth distribution function as well as influence of different de-noising methods to backscattering characteristics;achieve airborne spectrometer wave spectrum inversion algorithm,and further extract The Significant Wave Height and other parameters,quantitative evaluate the inversion outcome by compare with buoys data and ECMWF reanalysis data.results of the study are the following aspects.(1)At low wind speed,wave average backscatter coefficient values does not substantially change with wind speed,but wave backscatter coefficient asymmetry and anisotropy was positively correlated with wind speed.Under certain wind speed conditions,wave average backscatter coefficient with increasing incidence angle is gradually reduced until a certain value,then no change;asymmetry increases with incidence angle show slow growth trend,as the larger incidence angle,the growth trend more and more obvious,finally stabilized at a certain value;anisotropy increases with incidence angle show slow growth trend,and growth trends become more obvious.(2)Wave spectrum azimuth distribution function is a function of the azimuth angle and wave number,in all classic azimuth distribution function model,whether in upwind direction or downwind direction,K=K_p orK?K_p case,Donelan-Banner Model consist with test data mostly.(3)Among the three de-noising method,speckle calculated by Mathematics method is about 0.2 dB,followed by threshold method,approximately 0.4 d B,and both azimuth distribution characteristics entirely consistent,speckle noise value does not vary with changes in azimuth,with different from this two method,speckle calculated by cross spectrum method is about 2.5 dB,far greater than the mathematical method and the threshold method,with a bimodal azimuth distribution characteristic.(4)Airborne spectrometer can achieve high-precision wave spectrum inversion,where the significant wave height inversion accuracy mean absolute error of about 0.26 m,the relative error of about 7.18%,the maximum absolute error of about 0.41 m,the maximum relative error of about 11.5%,in full compliance with the need of waves retrieval precise.