Soil Surface Moisture Inversion Research On Salt-Affected Soils By Polarimetric Radar In Aird Areas

Spatial and temporal distribution of soil moisture information play a very significantposition in the disciplines of hydrology, climatology and plant ecology, it often beused as the input parameters in hydrologic models, climate models and ecologicalmodels and as the important indicators in prediction of drought, crop yield estimatesand other. Therefore, get the information of the wide range of soil moisture spatialand temporal distribution is an urgent problem. There are some restrictions in thetraditional measurement methods, optical remote sensing and passive microwaveremote sensing to get soil moisture. Studies have shown that active microwave remotesensing can compensate the shortcoming in the optical remote sensing and passivemicrowave remote sensing in the soil moisture monitoring applications and provide anew method and means for soil moisture monitoring.In the microwave band, the soil surface scattering of the soil electromagneticproperties is related to the surface roughness, dielectric constant and the moisturecontent. The dielectric constant and the moisture content have a great relationship, sothe surface roughness and the soil moisture surface microwave scattering propertiesare the main factors, so obtain these two important parameters is essential to researchin the surface scattering properties.The current SAR system is developing to the multi-polar, multi-angle direction, so it’spossible to research the relationship in the radar backscattering coefficient and the soilsurface parameters under the conditions of different polarization and incidence angles.This study based on comparing the three typical surface microwave scattering model(Oh model, Dubois model, the AIEM model) and used the AIEM model as atheoretical model to simulate and analysis the characteristics of soil surfacemicrowave scattering and proposed an empirical model to inversion surface roughnessparameters and soil moisture with multi-polarization SAR backscattering coefficientdata. The results of the study indicate that:(1) Comparing the Dubois model, Oh model and AIEM model, the results show thatDubois model has a different response with the actual situation to incidence angle and the dielectric constant. So we don’t recommend selecting this Dubois model for soilmoisture inversion of radar data. The Oh model can simulate the scatteringcharacteristics of cross-polarization but it has the large errors in the analog value ofsame polarizationscattering data, so we don’t recommend, too. The AIEM model cancharacterize the surface microwave scattering characteristics better both in simulatingthe same polarization scattering characteristics and the cross-polarization microwavescattering characteristics. Therefore,we should choose the AIEM model to simulate.(2) According to the principle of radar images, we used the NEST the DAT4A-1.5software to do the calibration of the study area RADARSAT2data and compareddemographic characteristics of different objects’ backscattering coefficient featureswith different saline degrees in HH, VV, HV and VH, On this basis, exploring thecharacteristics and the reason of different objects polarization from the perspective ofthe imaging principle of radar images and the physical mechanism.(3)Using the AIEM model to simulate the C-band radar signal’s backscatteringcharacteristics of the exposed salinization surface,analyzing the affection of the soilsurface parameters include the rms height, length, soil moisture and the radar systemparameters include the angle of incidence, polarization to radar microwave’s backscattering characteristics.Revealing the variation of the radar backscatteringcoefficient changes with these parameters and discussed the set of the ideal systemparameters in inversion of surface soil moisture.(4) Analyzing the relationship of the C-band same polarization and the cross-polarizer’s backscattering coefficient to the soil moisture and the combined roughnessparameters, considering the effects of radar incidence angle and established theexperience bare salinized surface scattering model. Finally，proposed a inversionprogram of soil moisture and surface roughness for the combinations of differentRADARSAT-2observational data.(5) Appling the inversion algorithm to Wei-Ku strangle oasis peripheral salinizedsoil test area and obtain the soil moisture spatial distribution figure and surfaceroughness space figure with the HH/VV,HH/HV,VV/VH three polarizationcombinations of RADARSAT-2data. The inversion results have a good correlation with the measured data of soil moisture, and compareing the precision of threepolarization mode,VV-VH polarization achieved high accuracy, and the corelationbetween the measured value and inversion value reached0.9148.