Measuring And Verifying Soil Moisture From Scale Of Pixel In The Desert Steppe Based On Cosmic-ray Neutron Method

Soil moisture is the basic component in the process of water cycle,energy cycle and biogeochemical cycle,and plays an important role in the fields such as hydrology,climate,agriculture and ecology.Remote sensing monitoring large-scale soil moisture depends excessively on the point soil moisture.While the large difference of spatial scale between these two methods makes it hard to guarantee the accuracy of remote sensing inversion.Therefore,this study carries out multi-scale cooperative observation and coupling verification of soil moisture at the point-,regional-and pixel-scale based on the cosmic ray neutron method at the regional scale,and.The study not only can enrich the soil moisture measurement technology,but also can provide the pixel-matching verification method for the remote sensing inversion.It plays an important role in scientific research such as hydrology,climate and ecology.The main contents and conclusions of this thesis are as follows:Soil moisture measuring with cosmic-ray neutron method in the desert steppe.Based on the soil moisture measured with oven drying,FDR and CRS,soil moisture in the desert steppe is measured with cosmic-ray neutron method.It is proved that this method could meet the requirements of scientific research and practical application and has a good development potential.Based on the analysis of the influencing factors such as vegetation and rainfall,it is proved that the vegetation in the study area has little effect on the measurement results,and it is proved that the response of CRS to rainfall is more sensitive than FDR.Based on the close correlation between neutron number and hydrogen,this study uses the weight of neutron intensity in the total neutron as the weight of soil moisture in corresponding position,constructs soil moisture scale conversion model,and puts forward the weighting method based on the neutron intensity.The correlation between the weighted average soil moisture based on neutron intensity and the CRS soil moisture was the best,and the correlation coefficient was 0.92.The scale conversion model is then established based on this weighting method.The actual spatial characteristics of the CRS measurement footprint are shown:? the footprint of CRS is not a standard cylinder,but a flat gyro type;? about the weights of soil moisture point measurement results,the vertical weight decreases with the depth and the horizontal weight also decreases with the distance.Remote sensing inversion of soil moisture with thermal inertia method.The soil moisture remote sensing inversion based on Landsat8 data and MODIS data were carried out by thermal inertia method respectively.In this paper,the MODIS night surface temperature product is combined to calculate the temperature difference ?T of Landsat8 data.Coupling verification of multi-scaling soil moisture.Based on the scale conversion model in the CRS footprint,the different spatial scale of different measurement methods including FDR point measurement,CRS regional measurement and remote sensing from pixel was unified.The coupling verification of the soil moisture observation results at different scales was carried out.Fitting CRS and FDR soil moisture,R2 is 0.84,RMSE is only 0.0128kg/kg,the relative error is almost less than 20%,indicating that the accuracy of cosmic ray neutron method of measurement is high and could meet the request of scientific research and practice applications.R2 of FDR soil moisture and remote sensing soil moisture from 30m/lkm pixel are both 0.74,while R2 of CRS and these two kinds of remote sensing results are0.82 and 0.81 respectively.It can be concluded that regional CRS soil moisture is better to verify remote sensing soil moisture than FDR.