Detection Of Reclaimed Soil Moisture Content In Coal Mine Subsidence Area Based On GPR

In order to quickly and effectively determine the change in soil water content and the spatial distribution characteristics of farmland in reclamation areas,we evaluated the accuracy of ground penetrating radar in detecting the surface soil water content,and analyzed the relationship between amplitude of radar signal attributes and soil water content.The soil water content of field parcel in the reclamation areas was inverted by using the radar wave average envelope amplitude(AEA)method,and then was compared with that derived by time domain reflectometry(TDR)method on the radar survey line.Within the study,we used two antennas frequency of 250 MHz and 500 MHz to detect the surface layer(0?20 cm)of reclaimed farmland in coal mine subsidence area by GPR.The results showed that GPR early-time amplitude had a strong correlation with soil water content.Among the four relational models,the logarithmic model had the best fitting result with R2 value of 0.995.According to the fitted curve,the greater the amplitude was,the smaller the water content was observed.If we obtained the amplitude value of the GPR signal at the corresponding position in the underground,the soil water content was calculated by the relational expressions which were found in the experiment.The soil water content obtained by AEA method was higher than that measured by TDR method,The AEA method got the similar soil water content with TDR method,L2 survey line in the first test(The antenna frequency of GPR was 250 MHz),the soil water content obtained by AEA method was 0.424 cm3 cm-3,and measured by TDR method was 0.401 cm3 cm-3 the mean relative error of the two methods was 0.023 cm3 cm-3;M2 survey line in the second test(The antenna frequency of GPR was 500 MHz),the soil water content obtained by AEA method was 0.174 cm3 cm-3,and measured by TDR method was 0.173 cm3 cm-3,the mean relative error of the two methods was 0.001 cm3 cm-3.The results acquired by the kriging interpolation from reclamation test area showed that the soil water content detected by GPR with 500 MHz frequency antennas more accurately than 250 MHz frequency antennas,in the first test,the surface soil water content of the GPR detection was 0.438 cm3 cm-3,and TDR method was 0.391 cm3 cm-3,and the overall measurement accuracy of GPR was 0.047 cm3 cm-3;in the second test,the surface soil water content of the GPR detection was 0.179 cm3 cm-3,and TDR method was 0.165 cm3 cm-3,and the overall measurement accuracy of GPR was 0.014 cm3 cm-3.To sum up,the results indicated that it is feasible to detect soil water content of the shallow stratum in reclamation farmland of mining area,the Loess Plateau,by using the method of early-time GPR signal AEA,which can get a distribution map of soil water content for large area continuously and accurately.