基于低频GPR的土壤累积入渗量的探测方法研究

农田尺度上土壤累积入渗量的准确获取是目前土壤入渗研究中的难题.通过土工模拟和灌水实验,探讨利用低频探地雷达(GPR)技术探测土壤累积入渗量的方法.在分析灌水前后GPR剖面特征的基础上,分别构建和对比了基于波速法和振幅法的土壤累积入渗量计算模型.结果表明,基于振幅的探测模型在精度和稳定性方面均优于波速法,反射波振幅模型精度高于地面波模型,利用反射波波谷1构建的累积入渗量的GPR探测模型的决定系数达到0.96.因此,使用低频探地雷达可以实现对土壤累积入渗量的准确探测.研究结果为农田尺度上土壤累积入渗量的探测方法提供了一种新思路,同时,也为GPR在土壤学领域中的进一步应用提供了科学依据.

Method for Measurement of Soil Cumulative Infiltration Based on Low Frequency GPR

Objective] Accurately assessing soil cumulative infiltration is essential to many field irrigation management and saline soil amelioration projects.However,the measurement of soil cumulative infiltration using the conventional methods has a number of defects,like costly,destructive and time-consuming.In addition,because soil infiltration is spatially variable,these point measurement techniques are of limited value in assessing the soil cumulative infiltration over a large area.The technique of Ground Penetrating Radar (GPR) can be used to collect the data non-destructively and instantly over a large area.Therefore,the technique is much higher than the conventional methods in potentiality and applicability for use to assess soil cumulative infiltration on a field scale.Method] In order to show that soil cumulative infiltration can be extracted from low frequency GPR data in the case of a loamy soil,a controlled soil and irrigation experiment was carried out.During the experiment,a 250 MHz antenna was used to collect GPR data for analysis of radargrams before and after the irrigation.Based on the radargrams obtained a soil infiltration estimation model was constructed using the electromagnetic wave amplitude recorded by the GPR.Then the model was compared with the electromagnetic wave speed model in accuracy and time window stability.Result] Results show that the determination coefficient of electromagnetic wave speed and soil cumulative infiltration was 0.8,0.1 and 0.12 in the 2.2 m time window,1.57 m time window and total of the samples,respectively,indicating that the electromagnetic wave speed model depends on time windows,and is low in stability and precision,so the model is not good enough to reflect soil cumulative infiltrations.While GPR amplitude was found to be more sensitive to variation of soil cumulative infiltration.Among the electromagnetic wave amplitude parameters,the determination coefficient of trough amplitude of Reflection Wave Ⅰ and soil cumulative infiltration was 0.999,0.986 and 0.962 in the 2.2 m time window,1.57 m time window and total of the samples,respectively,and the determination coefficient of the trough amplitude of Reflection Wave Ⅱ and soil cumulative infiltration was 0.981,0.999 and 0.925,respectively,while the determination coefficient of trough amplitude of the ground direct wave and soil cumulative infiltration was 0.920,0.965 and 0.943,respectively.By following the principle of the highest determination coefficient,this paper selected the trough amplitude of Reflection Wave Ⅰ in constructing the GPR model for detection of soil cumulative infiltration,thus bringing the determination coefficient up to 0.96.Conclusion] In brief,the electromagnetic wave amplitude model is higher than the wave speed model in precision and stability,and can be used to monitor and estimate soil cumulat iveinfiltration.The trough amplitude of Reflection Wave Ⅰ is an ideal indicator to be used to effectively monitor soil cumulative infiltration.Therefore,the low frequency GPR can be used to accurately detect soil cumulative infiltration.All the findings in this research may provide a new way for the detection of soil cumulative infiltration on field scales,and also a scientific basis for further application GPR to the field of soil science.