SAR Doppler Center Shift Method Flow Measurement Error Modelin

Ocean current,one of the common forms of seawater movement,is the most fundamental element in the field of oceanography and meteorology.Thus,the scientific observation of ocean current is of great significance to the development of marine science.Compared with in situ observation and other remote sensing measurements,synthetic aperture radar(SAR)Doppler centroid anomaly(DCA)method has the advantages of high resolution,wide coverage,low cost,and wide business scope,which is gradually becoming an indispensable method of ocean current measurement in remote sensing.Herein,the SAR Doppler centroid estimation standard deviation(STD)is imperative in current-measuring accuracy assessment and error budget computation when designing the instrumental parameters for a new SAR system.However,the main problem with the DCA method is the lack of well-developed STD analysis model,and the existing formulas for SAR Doppler centroid estimation STD suffer from various limitations,especially for a dynamic sea surface.In this study,we derive an improved version of these formulas through three steps.First,by considering the ocean wavenumber spectrum information,a new strategy for determining the number of independent samples of the sea wave velocity field is adopted in the new formula.This is contrary to the method used in the existing formulas,where the number of SAR geometric resolution cells is taken as the number of samples assuming that adjacent SAR resolution cells are statistically uncorrelated.Second,the pulse repetition frequency and Doppler bandwidth are decoupled in the new formula,unlike in the existing formulas where they are unchangeably related to each other.Third,the effects of thermal noise and Doppler aliasing are jointly quantified in a mathematically exact manner instead of being treated separately,as in the existing formulas.Comprehensive Monte-Carlo simulation results for the ocean surface show that the new formula has a better performance in predicting the Doppler centroid estimation STD than the existing formulas.