Study On The Retrieval Of Soil Moisture Of Vegetation Coverage Surface By Active And Passive Microwave Remote Sensing

Water is the most important resource on the earth,and it is the basic element of human life.Soil moisture is an important part of the global terrestrial ecosystem,which controls the energy exchange between land and atmosphere.Microwave remote sensing has the characteristics of macro,high efficiency and economy,it is particularly sensitive to moisture and suitable for soil moisture monitoring,which has a great advantage over traditional visible and infrared remote sensing.Microwave remote sensing is one of the most effective methods to monitor soil moisture.Passive microwave remote sensing is more sensitive to soil moisture,it can be used for inversion of soil moisture content.Active microwave remote sensing is more sensitive to the surface morphology and vegetation types.It is often used to estimate the relative value of soil moisture.The spatial resolution is usually higher than that of passive microwave.The advantages of active and passive microwave remote sensing are complementary,The joint application of the two methods can give full play to their respective advantages,especially in the soil surface covered with crops,can simplify the process of soil moisture monitoring and improve the quality of soil moisture estimation.At present,more and more attention has been paid to the cooperation of optical and microwave remote sensing in the world.Many satellites are equipped with microwave and optical sensors.Therefore,the optical and microwave remote sensing has become an important direction of the development of remote sensing inversion,the combination of the two will be more accurate inversion of surface parameters,to maximize the role of remote sensing satellites.In this paper,the advantages of optical microwave remote sensing,using active and passive microwave model as the main method,supplemented by optical model.The vegetation parameters retrieved from the optical model are input into the microwave model,which can be used to retrieve the surface soil moisture and improve the inversion precision of soil moisture.In this study,the soil moisture retrieval experiment was carried out in the area of Heihe basin,which is a flat area with uniform vegetation coverage.Ba sed on this,two kinds of soil moisture retrieval methods are proposed:1.By using cloud model to remove effects of vegetation layer water content on soil moisture information generated,and cmbined with active microwave inversion method,soil moisture estimation is realized.2.Based on single frequency and single incident angle,by fusing the L-band radiometer ground observation data and L-band ALOS PALSAR radar image data to establish the relationship between soil volume water and radar backscatter,considering the influence of vegetation index VI on soil water content to obtain the soil moisture values.The main results of this study include the following aspects:(1)This paper analyzed the mechanism of evaporation and transpiration of farmland water,the effects of vegetation,soil and roughness on satellite radar echo signal,and the characteristics of optical satellite Landsat-5 image,radar satellite ALOS-PLASAR data and radiometer remote sensing data.(2)Because of the influence of vegetation coverage on radar backscatter in the observation area,this article use the cloud model to remove the scattering contribution of soil layer vegetation scattering model.This paper is based on the crop covers the surface of the back scattering mechanism,using semi-empirical water cloud model to deduce the vegetation water contribution from radar scattering signal.Finally,the high resolution remote sensing inversion of soil moisture under vegetation cover was carried out.(3)Based on the PLASAR data,the active radar is used to retrieve the soil moisture,and the corrected radar image and TM image are processed by the method of resampling to form the 30 m resolution image data.Then,the linear relationship between the backscattering coefficient of soil and the soil moisture was established under the HH and HV polarization,At last,estimation of soil water content of vegetation cover in the middle resolution.(4)This study selects 10 m high-resolution PLASAR radar satellite data and 120 m low resolution radiometer data,based on scale fusion,considering the influence of vegetation index VI.Analysis of the mathematical relationship between the three,Thus,the active and passive microwave joint inversion algorithm of soil moisture in the resolution of 30 m was developed to realize the estimation of soil moisture content in a large scale.(5)Finally,by using the soil moisture data resolution under observation area,were carried out to validate the active microwave soil moisture retrieval method and passive microwave combined inversion algorithm,and soil moisture on the retrieval precision of simulation value comparison and evaluation.