The Research Of Rice Methane Emissions Based On SAR Image And Ground-based Scatterometer

Rice is important food crop which is widely distributed in the world and provides staple food for one third of the world's population.Therefore,the rice has limited the world food security,improving the safety of agricultural products and the safety of plant genetic resources,maintaining regional peace and stability,food and fresh water resources,adapting to population growth and economic sustainable development.Meanwhile,due to the special growth environment and planting methods,rice can only be planted in wetland ecological environment.Therefore,unlike other dryland ecosystems such as wheat and maize,rice plays a role as a greenhouse gas emitter in the global greenhouse effect.Rice,which is the origin of the world's rice crop,accounts for half of all food crops,so China is regarding as world's leading emitters of greenhouse gas emissions for a long time.There will be cloud,fog,rain and other weather at the rice growing area in most of the time,it is difficult to obtain the full growth period of rice real-time optical remote sensing image.Microwave remote sensing unique information acquisition mechanism to observe the ground target physical and geometric characteristics,and all-weather,all-day and penetrating and other characteristics,it is high efficiency and sustainable to monitoring the methane emissions of rice field.However,the mechanism of microwave scattering is very complicated and different,and the research is lagging behind for the interaction between microwave and surface and vegetation,so it is necessary to study and explore relevant theoretical and technical problems.These years,The continuous development of the space-borne SAR platform development and the improvement of radar observations.In order to make efficiently use of the data of the large-scale and full-time of these radar remote sensing data,it is urgent to study the mechanism of model the scattering objects and parameter quantitative inversion algorithm.Firstly,The foundation of microwave remote sensing data and methane emission observation data are built based on the land-based scattering measurement system,the rice scattering experiments were carried out in three whole growing periods in 2010,2011 and 2012,and the wetland scattering experiment was carried out in 2013.The microwave scattering characteristics of rice were analyzed.The experiments mainlyinclude backscattering coefficients measurements of four bands(L,S,C,X),full polarization(HH,HV,VH and VV),different azimuth(45°,90°,135°)and different incidence angles(0°-90°);collections and data processing of rice and wetland methane samples using synchronous static box method in 2011,2012 and 2013;ground data of the rice field such as rice biomass,canopy thickness,height,the number of trees,the density of the rods,the number of leaves,the water surface of the underlying surface,the soil water content and the soil roughness.The incidence angles scattering characteristics,time domain scattering characteristics and scattering values and spatial aggregation scattering characteristics of rice in different growth stages were studied,which provided experimental basis for the modeling of rice scattering and the inversion of relevant parameters.Secondly,Based on the microwave backscattering model of rice,the inversion model of significant parameters affecting methane emission was established.Among them,the empirical model of the system parameters and the empirical model of the growth parameters(canopy height,leaf area index and rod density)are given according to the different input value.Modeling is built and the empirical model of multiple growth of rice was established.The semi-empirical model establishes the water cloud model of rice and the improved water cloud model according to the different consideration of scattering items.The empirical parameters of the model were established by using the measured data.The theoretical Michigan scattering model was established according to the radiative transfer theory.It has been modified and simulated for the parameter characteristics of rice and underlying surface.Then,the water body information was extracted through the secondary and tertiary weak scattering,which include the underlying surface water information.The accuracy of the inversion of these parameters is verified by comparing the simulated and measured data with the water information.And it finally provides the theoretical basis for the establishment of rice methane inversion model.Thirdly,analyzes the main influencing factors of rice methane emission by microwave scattering process and biogeochemical process of paddy field and the ecological process and parameter inversion algorithm of methane productionBased on the improved model of agricultural ecological process,the experience and semi-empirical model of microwave methane emisiion in rice were established.First of all,the improvement of the main empirical parameters of affecting methane emission isrealized by using the backward scattering coefficient on the basis of model,which also compensates the insufficiency of the measured data.Then,according to the difference of the surface water of the rice under the tice growing process,the methane emission model is divided into two different kinds of emissions,including water and water without water by using the backward scattering coefficient.In addition,when the upper layer of soil is not covered with water,the input of methane emission model can be determined by the soil moisture content of the inversion,which is more close to the real environment rice methane emissions.Finally,the model of methane emission based on active SAR data was established,and the mapping of rice cover area and the extraction of methane are realized.Although the measurements of land-based scatterometer and spaceborne SAR are not exactly the same,the final scattering coefficients are consistent.Therefore,the quantitative inversion model of the rice and the underlying surface parameters based on the land-based scatterometer measurement data,can be applied to the SAR image data processing.Making ASAR and Radarsat-2 image data synchronization and applying it to the rice classification and biomass inversion,the inversion of the methane emission flux in the experimental area was realized by using the established empirical and semi-empirical rice microwave methane emission model.The methane emission curve from the actual methane emission measurement shows that the SAR image can accurately invert the methane emission flux of rice at different times in the experimental area.There is a complex interrelationship between the twoVegetation microwave scattering mechanism and rice backscattering.On this basis,a microwave scattering model is established to improve the radar remote sensing information extraction and quantitative inversion.Based on the microwave scattering mechanism of rice,the parameter inversion algorithm and the agricultural ecological methane emission model,this paper puts forward the experience and semi-empirical model of methane emission flux based on SAR data using a large amount of experimental data.In partucular,the scattering coefficient of rice is measured based on the land-based scatterometer system,and the microwave scattering ground test data of multi-round rice growing season are observed firstly.Then,an effective rice scattering model is established and improved using the microwave scattering theory.Then the polarized and time-domain characteristics of rice microwave scattering were analyzed qualitatively andquantitatively.The inversion algorithm of rice methane emission parameters was established.Finally,through the established microwave experience and semi-empirical rice methane emission model,simultaneous experiment of the region to achieve the SAR image on the rice and wetland vegetation biomass growth parameters inversion and methane emission monitoring demonstration for large-scale monitoring of wetland environment in the extraction of vegetation information to provide theoretical and experimental basis.