Ground Verification Method Based On Ground-penetrating Radar For Remote Sensing Monitoring Of Soil Water And Its Scaling Problem

Accurate and quantitative monitoring of soil moisture is of great significance to the study of regional water cycle movement,monitoring the occurrence and development of drought,guiding agricultural production practices and rational regulation of water resources.With the rapid development of remote sensing technology,rapid acquisition of large-scale soil water by remote sensing methods have attracted wide attention.Because of the great differences of measuring scale between the ground measurements and satellite data,accuracy verification of remote sensing products by the traditional soil water measurements has the scale problem.There is a lack of scientific methods for soil water validation at the pixel scale between soil water measurement and remote sensing observations.It is the main scientific problem of this paper to verify the results of the remote sensing inversion of soil water by means of convenient and rapid measurement of accurate soil water measurement.In order to study the verification method by ground penetrating radar for remote sensing data of soil water,the accuracy and the influencing factors of soil water measurement by ground penetrating radar was analyzed.By soil water validation experiments based on ground penetrating radar at pixel size,the spatial heterogeneity and scale effect of soil water at the pixel scale were analyzed by means of geostatistics.The method of soil water verification based on ground penetrating radar was established by using random combination method.The accuracy of soil water data by remote sensing inversion at 30m and 1km was evaluated by soil water verification method based on ground penetrating radar.The main achievements of the paper are as follows:(1)The accuracy of the ground penetrating radar is verified by the gravimetric method.The soil water measurement results of the ground penetrating radar are consistent with the gravimetric method.The Topp formula is more suitable for calculating the soil water content in the desert steppe than the Roth formula.Compared with the traditional gravimetric method and the time domain reflectometer,the ground penetrating radar is a reliable and suitable method for soil water measurement on the field scale.(2)The spatial variability of soil water and its scale effect were analyzed by geostatistics.The effect of sampling size on the spatial variability of soil moisture was significant,and the maximum correlation distance of soil water increased with the increase of sampling scale.For the same scale,the spatial variability of the sample is different from that of the terrain,micro-topography,soil and vegetation,and the coefficient of variation is in the range of 12%-19%.(3)A ground verification method for soil water remote sensing monitoring based on ground penetrating radar is proposed.Through stochastic combination method and universal kriging method,we find that:When the relative error of the measured value of the soil water is required within 7%,two diagonal measuring lines are laid out in the pixel using the ground penetrating radar.When the relative error of the measured soil water measurement is within 5%,four well pattern measuring lines are laid out in the pixel using the ground penetrating radar.It can describe the higher spatial resolution of soil water compared to other methods.(4)The remote sensing monitoring results of soil water with 30m and 1km resolution were verified by ground penetrating radar method;the accuracy of 30m and 1km resolution soil water remote sensing inversion was evaluated according to the groundwater remote sensing monitoring method of groundwater radar.According to the results of soil water inversion at 30m resolution,the results of the gravimetric method are close to those of the two lines,and the results of the four lines are more stable than the gravimetric method and the two lines,which is consistent with the conclusion of groundwater verification method for groundwater remote sensing monitoring ground penetrating radar.For the soil water inversion with 1 km resolution,the relative error of the 1 km pixel soil water inversion gradually decreases with the increase of the soil water measurement scale.In order to accurately verify the remote sensing results of soil water with a resolution of 1 km,it is suggested that two diagonal lines or four well pattern lines should be arranged in 1 km of pixels.The average is the soil moisture content of the pixel.