Simulation And Analysis Of Radar Altimeter Echo Based On Electromagnetic Scattering Characteristics

The study of electromagnetic scattering characteristics of random rough surfaces is of great significance to microwave remote sensing,target detection and radar imaging.Satellite radar altimeter is a significant marine microwave remote sensor.Through the survey data of satellite radar altimeter,we can invert ocean parameters.However,when the altimeter is close to the land and there are islands and other non-ocean rough surfaces under the footprints,the waveforms obtained are distorted,and do not conform to the ocean model.As a result,the inversion of ocean parameters has large errors and is even unreliable.In view of this,based on the characteristics of random rough surface electromagnetic scattering,this paper calculates the scattering coefficient of common target rough surface,and simulates and analyzes the altimeter pulse echo according to the principle of the interaction between altimeter electromagnetic pulse and rough sea surface and land.To a certain extent,understand the physical principles and electromagnetic characteristics of the offshore echoes contaminated by the land echoes,and play a positive role in shortening the unusable distance.The main work of the paper is as follows:1.The concrete process of establishing rough surface by Fast Fourier Transform method is given,and the common Gaussian spectrum,PM spectrum and exponential spectrum are simulated in 1D and 2D random rough surface,and the surface profile characteristics are analyzed.The dielectric constant models of common substances are introduced,including seawater,sea ice,and soil.The influencing factors of the dielectric constant are analyzed,and the dielectric constant is calculated under certain conditions.2.In order to ensure the correctness and accuracy requirements of the calculation of the scattering coefficient of the rough surface,the scattering coefficient of the random rough surface was calculated using the Kirchhoff Approximation,Method of Moments and Finite Difference Time Domain method,and the calculation results of the three methods were compared under different conditions.The results show that the calculation results of the three methods are consistent.3.The radar altimeter echo is simulated.Based on the radar altimeter echo principle,the result of the rough surface scattering coefficient is used to calculate the echo power of each scattering surface,and the echo process of the radar altimeter is simulated to obtain the echo curves of different detection targets.including ocean echoes under different wind speeds and echoes of composite targets.4.Fitting verification of echo waveform.First,use the least square method to Fitting inversion between ocean echo and the second-order approximate model to obtain the curves of the scattering coefficient and effective wave height at different wind speeds,which are more in line with the theoretical numerical curve.Then,the measured data of ocean satellites are introduced,and the backscattering coefficients and effective wave heights obtained by fitting and inversion are consistent with the reference results provided in the satellite data.Finally,under the condition that the satellite's measured ocean echo and electromagnetic scattering simulation ocean echo are equivalent and consistent,the inshore echo is simulated,then analyze and study the influence of inshore islands,beaches and reefs on the rough sea echo.The similarity between the electromagnetic scattering simulated echo and the measured inshore echo is analyzed,which provides an effective way for the inversion of ocean parameters from the inshore echo,and also provides theoretical basis and data support for the detection of ocean targets.