Simulation Study On L-band Scatterometer System Of Salinity Remote Sensing Satellit

Satellite remote sensing of sea surface salinity is of great significance for both ocean dynamics environment and global climate change studies.For the microwave remote sensing of sea surface salinity(SSS),the brightness temperature changes induced by the sea surface roughness are equivalent or even larger than those caused by the sea surface salinity.Consequently,the remote sensing of sea surface salinity should not only use L-band microwave frequency,which is sensitive to SSS,for accurate brightness temperature measurement,but also use L-band scatterometer to estimate the sea surface roughness simultaneously.It is conducive to improving the accuracy of salinity measurement.For this reason,the first Chinese Ocean Salinity Satellite will use a new type of active/passive microwave salinometer MICAP(Microwave Imager Combined Active/Passive)as one of the payloads.MICAP consists of an L/C/K multi-band one-dimensional integrated aperture radiometer and an L-band phased array digital beam forming scatterometer.The L-band scatterometer adopts a new observation system of one-dimensional phased array push-brooming type,which is different from the previous scatterometers.Its observation geometry,pulse timing,and signal processing methods need to be reconsidered.This paper studies the L-band microwave scatterometer onboard the first Chinese Ocean Salinity Mission.A simulation model is developed for the L-band multiple-beam pushbrooming microwave scatterometer system.With the simulation model,the impact of radar pulse parameters,including the signal bandwidth and the pulse configuration of different polarizations,on the system performance is analyzed,and the design is optimized accordingly.The results show that,under the baseline parameters of the L-band scatterometer,the pulse bandwidth is 1.5 MHz and the pulse repetition frequency is 100 Hz,the accuracy of the system backscatter measurement can be effectively improved by accumulating multiple pulses at the same wave position and appropriately increasing the number of emitted pulses at the HH polarization and wave positions farther from the nadir point,which makes the overall accuracy of the co-polarized backscattering measurement accuracy under different wind speed conditions better than 0.1 d B.Furthermore,in order to investigate the specific signal processing process of ten received channels of L-band scatterometer,and the effect of system amplitude phase error on the pulse compression performance,signal measurement simulation experiments are carried out in this paper to simulate the actual measurement of the scatterometer after adding various types of amplitude phase errors using different error signal models.The pulse compression results in the one-dimensional range direction are evaluated by combining the peak-to-side lobe ratio and the main lobe width of the signal.The results show that periodic errors change the pulse pressure waveform of the linear chirp signal,resulting in paired side lobe echoes,and this effect is more significant when the amplitude and phase are distorted at the same time.Aperiodic errors lead to the offset of the resolution target,the reduction of the echo signal-to-noise ratio and the asymmetric distortion of the main lobe structure.Finally,due to the special observation regime of the L-band scatterometer,it has only a single viewpoint observation within a wind vector cell.In this paper,the polarized coherent geophysical model function is introduced in the wind field inversion process.And the performance of L-band scatterometer wind field measurements under different noise conditions is analyzed by using Monte Carlo simulation methods.The results of the paper are of great reference value for the design of system,signal processing and sea surface wind field observation of Chinese future salinity remote sensing satellite scatterometer.