Study On Ocean Surface Current Retrieval By Along-track Interferometric SAR

Ocean surface current is one of the most common movement forms of seawater,and it is also the most basic,important element in marine science.Ocean surface current has a big influence on marine disaster reduction,maritime search and rescue,coastal zone building,fishing,shipping and pollutant diffusion.The synthetic aperture radar(SAR)along-track interferometric(ATI)method has the advantage of all-day,all-weather,wide swath and high resolution.It is an promising method for ocean observation.An ideal ATI-SAR system is the basis for ocean surface current retrieval,so it is necessary to analyze the factors which influence on ocean surface current measurements by ATI-SAR based on the GF-3 satellite standard strip mode.The polarization mode,incident angle,ATI effective baseline and Noise Equivalent Sigma Zero(NESZ)are studied by simulation.Finally,the ideal system parameters for GF-3satellite ocean observation are given: the polarization mode is VV,and the incident angle should be in 35°~45°,and NESZ should be better than-20 dB.Because of the problem that the single satellite can`t have a long baseline to obtain a good observation result,the ideal ATI effective baseline for satellite formation is analyzed.As a result,when the ATI effective baseline range from 28 m to 56 m,GF-3 satellite can have a good result of current measurement.And this simulation result also provide reference in SAR system design.Secondly,data of GF-3 satellite ATI mode are used to demonstrate the process of obtaining the interferometric phase image.The main processing steps includeing:reading and displaying the SLC data,the image registration by using multiple correlation coefficient,obtaining the interferometric phase image,reducing the image noise by using circular period mean filter,multi-look processing is used to reduce the speckle noise and the needing number of looks is analyzed,phase unwrapping method,the nonzero phase caused by channel imbalance should be corrected,the azimuth offset caused by moving target also should be calibrated.At last,according to the analysis results of system parameters,using ideal ATI simulation data to retrieve ocean surface current.Firstly,a series of interference processing are used to obtain the good interferometric phase image,and then the iterative method for ocean surface current retrieval is used to retrieve ocean surface current,and the error of retrieval is about 0.04m/s.Due to the fixed step in iterative method,using adaptive variable step size to optimize the method.Compare these two steps,the result indicate that the adaptive variable step size can improve accuracy.