基于探地雷达早期信号振幅包络值的黏性土壤含水率探测

Detection of cohesive soil water content based on early signal amplitude envelope of ground penetrating radar

为了验证探地雷达探测黏性土壤含水率的精确性,利用探地雷达早期信号振幅包络法平均值方法(average amplitude envelope,AEA)对降雨前后野外农田表层(<0.3 m)土壤含水率进行探测,并利用TDR探测土壤含水率以作对比。研究结果显示,土壤水分含量与黏粒含量具有一定相关性。在大面积范围内(1000 m长测线),TDR2次探测土壤平均含水率分别为14.16、16.91 cm^3/cm^3;AEA方法2次探测土壤平均含水率分别为14.62、17.88 cm^3/cm^3,与TDR实测含水率差值分别为0.46、0.97 cm^3/cm^3,2种方法探测所得含水率具有极显著的相关性(P<0.01),相关系数分别为0.825、0.814。小范围内(40 m×40 m)降雨前后TDR 2次探测黏性土壤含水率分别为14.11、16.77 cm^3/cm^3。AEA 2次探测土壤平均含水率分别为14.86 cm、17.46 cm^3/cm^3,比TDR实测含水率分别大0.74、0.69 cm^3/cm^3。AEA与TDR探测所得含水率相关系数分别为0.701、0.827(P<0.01),研究结果表明利用探地雷达AEA方法能够获得与TDR实测精度相近的黏性土壤含水率。利用常规探地雷达共中心点法及共偏移距方法对研究区黏性土壤含水率探测结果显示,这2种方法均不能有效地探测黏性土壤含水率。

Cohesive soil is a common soil medium in land resource evaluation and farmland land consolidation. The dielectric properties, physical, chemical properties and mechanical properties of cohesive soils are closely related to the soil water content. Ground penetrating radar(GPR), as a fast and non-destructive detection tool, can provide information about electromagnetic wave propagation in the ground, so as to realize the detection of underground media. Especially in soil water content detection, ground penetrating radar(GPR) has been widely used. However, due to the complex composition of cohesive soil and the fast attenuation of electromagnetic waves in cohesive, GPR is rarely used in the detection of water content in cohesive soil, which greatly restricts the application and development of GPR technology. The early signal of radar wave is the signal generated by the superposition of air wave and ground wave due to the small distance between the transmitting and receiving antenna, and it can also reflect the physical properties of the surrounding medium. The results show that there is a certain correlation between the early signal amplitude, waveform and soil water content. For cohesive soils, most of the radar wave energy has been lost near the surface due to the high conductivity, so ground waves are more useful waveform signals than reflected waves. In order to verify the accuracy of GPR, AEA(average amplitude envelope) method in detecting the water content of cohesive soil, this study used GPR to detect the soil water content of field farmland(<0.3 m) before and after rainfall, and TDR was used for comparison. The results showed that there was a certain correlation between soil water content and clay content. In a large area(1 000 m long survey line), the average soil water content detected by TDR was 14.16, 16.91 cm^3/cm^3, respectively. The average soil water content detected by AEA method was 14.62, 17.88 cm^3/cm^3, respectively, and the difference between them and the measured water content by TDR was 0.46, 0.97 cm^3/cm^3, respectively. The water content detected by the two methods had extremely significant correlation(P<0.01), and the correlation coefficients were 0.825 and 0.814, respectively(P<0.01). Within a small range(40 m×40 m), the water content of cohesive soil detected by TDR before and after rainfall was 14.11, 16.77 cm^3/cm^3, respectively. The average soil water content detected by AEA method was 14.86, 17.46 cm^3/cm^3, respectively, which were 0.74, 0.69 cm^3/cm^3 higher than that measured by TDR. The correlation coefficients of water content detected by the two methods were 0.701 and 0.827, respectively(P<0.01). Analysis of the water cut plane distribution of the two detection methods showed that the soil water content detected by AEA method was similar to TDR method. The results showed that ground penetrating radar(GPR) AEA model could accurately detect the water content of cohesive soil. The conventional GPR common mid point method and fixed offset method were used to detect the water content of cohesive soil in the study area. The results showed that neither of the two methods could effectively detect the moisture content of cohesive soil.