Study On Soil Moisture Inversion Under Submerged Vegetation Cover Surface

Soil moisture is an important state parameter in the water circle,biosphere and atmospheric circle,and it is a direct factor of surface water heat exchange.It affects people's activities of production and life.Therefore,it is concerned by many disciplines and industries,such as agriculture,meteorology,hydrology and transportation.There are mainly two methods for monitoring soil moisture: the traditional measurement method based on the field point measurement and the remote sensing technology monitoring method.The remote sensing technology monitoring method has the advantages of wide monitoring area,short cycle,high efficiency,wide data source,large amount of data,low monitoring cost and so on.The advantages of remote sensing technology in long-term and dynamic monitoring are more prominent.Active microwave remote sensing for soil moisture monitoring is a hot topic at present.It is an important factor that affects the accuracy of soil moisture inversion because of the absorption and scattering of the surface vegetation cover to the backscattering coefficient of the microwave backscatter factor.So it is a hot research direction in the field of soil moisture inversion to study how to retrieve the soil moisture of the mat surface under the vegetation cover.Based on the project of "military surveying and mapping professional processing and service system-geospatial information fusion processing subsystem",the paper selected the Linze grassland in Heihe River Basin of Gansu Province as the research area,and studied the soil moisture inversion of the low vegetation covered surface under the low vegetation coverage in the study area.The study area is located in arid and semi-arid areas of Northwest China.Vegetation covers mainly low vegetation including shrubs,reeds,farmland and grassland.Based on the consideration of removing the influence of vegetation cover on the surface soil moisture inversion,the paper combines the characteristics of Landsat-5 optical remote sensing data with high spectral resolution,rich ground information and so on,as well as the high spatial resolution and penetration of ENVISAT ASAR active microwave.Through the inversion of the soil moisture inversion of the bare soil and the inversion model of the soil moisture of the vegetation covering the surface,the water cloud model and the AIEM model are selected to invert the soil moisture of the underlying surface of the vegetation,and the effect of the vegetation on the backscatter coefficient(VV polarization)of the radar is eliminated by using the water cloud model.AIEM model is used to generate LUT look-up table to retrieve soil moisture.In this paper,NDVI and NDWI are used to improve the estimation of the backscatter coefficient and double decaying factor in the water cloud model,and form a group of water cloud models.Based on the consideration of soil moisture inversion,an exponential strategy type matching method,IMMM(Index management matching method),is proposed to invert soil moisture and use construction.The strategy matching index was obtained by combining the NDVI and NDWI vegetation index strategy of the water cloud model,and the optimal function of vegetation influence was eliminated through the selection of the strategy matching index.Thus,the effect of vegetation cover on the backscatter coefficient was better eliminated and the accuracy of soil moisture inversion was improved.