The Study On Ocean Parameter Inversion And Offshore Re-tracking Algorithm Based On Satellite Radar Altimeter

As an active sub-satellite microwave remote sensor,the satellite radar altimeter is mainly used to observe sea surface parameters.The further processing of the measured data can be applied to marine geophysics,ocean dynamics,and marine environment monitoring.In the far-sea,a relatively regular ocean echo waveform is received,and the echo model can accurately invert the sea surface parameters to meet the engineering practice requirements.However,in the offshore,due to the influence of terrestrial terrain on the microwave signal,the echo waveform received by the altimeter changes or even loses lock,which greatly affects the effectiveness of the altimeter offshore echo and the inversion accuracy of the offshore parameters.This paper focuses on the research of echo waveform,which is an important parameter in the altimeter data.Firstly,the rough sea surface is formed based on the Monte Carlo method,and the echo waveform are simulated by the radar equation at different wind speeds.Secondly,the echo model and parameter inversion algorithm are analyzed and studied in detail.The first-order model and the second-order approximation model of the development of Hayne model are compared.The results show that the difference between two models' inversion results is nearly the same when the misdirected angle is small.Otherwise,the second-order model is more accurate.So this paper uses second-order model to simulate echo,and then inverses significant wave height.I In addition,in the wind speed inversion,the dual-band backscatter coefficient and the significant wave height are taken as input parameters of a neural network to acquire high-precision wind speed inversion formula.Then the offshore echo waveforms are studied in detail from the following three aspects:(1)of offshore echo waveforms,the echo waveforms of China's offshore waters are analyzed,and several commonly used waveform re-tracking algorithms are introduced.(2)Calculate the unusable distance of each track data relative to the shore point by using the half power point obtained by the OCOG algorithm.(3)Calculate the correction amount using the waveform re-tracking algorithm for the echo waveform outside the unavailable dis-tance,and analyze the difference between the algorithms.Aiming at the distortion of the echo waveform in the unavailable distance,a method of constructing the waveform is proposed.Using the characteristics of the far-sea echo waveform,the trailing edge of the echo waveform is constructed to form a structural echo.The re-tracking algorithm is applied to the constructed waveform,and relevant verification is performed,which provides a new idea for offshore waveform reconstruction.Finally,for the V-type signal of the thermal noise region of the echo sequence,the principle of its generation is analyzed,and it is applied to the detection of sea surface objects through the measured waveforms in the offshore,which provides a new application for the altimeter.In summary,the research results of this paper have a good reference value and application significance in the work of altimeter parameter inversion and offshore waveform reconstruction.