Study On The Coastal Echo Processing Method For Satellite Radar Altimeter

Radar altimeter is an effective tool in ocean exploration.The echo waveforms received by the altimeter can be used to obtain the sea surface height,the significant wave height and the backscatter coefficient by ground retracking technology.At present,the altimeter data processing technology in the open sea has been very mature.However,there are a large number of waveforms affected by land reflections near the coast,whose shape are different from the echo waveform from the open sea.These waveforms are usually called as “non-ocean waveforms”.Using the traditional ocean waveform processing method to process coastal echoes will lead to the decrease of data utilization and the deterioration of product accuracy.Therefore,the application of radar altimeter in the offshore regions still needs to be explored.In this paper,the principle of radar altimeter measurement and the rationale how the echo waveform is formed are discussed,and the retracking algorithms of land and sea are investigated.Then,the characteristics of coastal echo waveforms of the HY-2B satellite radar altimeter and Jason-2 satellite radar altimeter are analyzed,the coastal non-ocean waveforms are divided into three categories: ocean-like waveform,land-like waveform and sharp conical-shaped waveform.On this basis,this paper proposes a coastal waveform processing approach based on neural network classification,which include echo classification and echo retracking.The echo classification is implemented by the Back Propagation Neural Network,and the echo retracking is processed according to the category.For ocean-like waveforms,a retracking method for removing abnormal peaks is proposed,which effectively improves the retracking success rate and retracking accuracy of ocean-like waveforms.The method in this paper is applied to the coastal data processing of HY-2B satellite and Jason-2 satellite,and the results show that the success rate of retracking and the validity of data are improved.Using the data from the Zhiwan Island tide gauge station,the sea surface height measurements obtained by HY-2B satellite reprocessing are evaluated.The sea surface height obtained by the reprocessing is more stable,and the standard deviation is 6.5cm,which is better than the 14.5cm of the original untreated SGDR product.