GPR Attribute Analysis Technology And Its Application In LNAPL Contaminated Soil Detection

Liquid which is lighter than water and insoluble in water is called Light Non-aqueous Phase Liquid(LNAPL).Petroleum is the main representative of LNAPL.It will inevitably leak during production,storage,and refining,causing soil and groundwater pollution.Because LNAPL contaminant is concealed,it is very difficult to detect and judge the degree of pollution through observation.Therefore,finding a fast,efficient and non-destructive LNAPL contaminated soil survey method is of great significance for analyzing,evaluating and repairing underground oil pollution.Ground penetrating radar(GPR)is an electromagnetic non-destructive detection technology,it's suitable for detecting LNAPL Contaminant.The traditional ground penetrating radar data processing method generally has a common effect on the detection of such contaminant having a small difference in relative dielectric constant from the surrounding medium.The GPR attribute analysis technology can extract the descriptive attributes from the GPR data,characterize the underground anomalous body,and improve the interpretation ability of the ground penetrating radar data.In order to make better use of GPR data to obtain information on underground LNAPL contaminant,and to understand its distribution range and characteristics,this paper studies some ground penetrating radar attribute analysis techniques suitable for LNAPL pollution detection,including instantaneous attribute analysis,polarization attribute analysis,similarity attribute analysis,and energy attribute analysis.Through the physical model test in the indoor sandbox and the field LNAPL contaminated soil detection,we study about how the ground penetrating radar attribute analysis technology characterizes the LNAPL contaminated soil characteristics,and how to finely image the LNAPL contaminated soil.In this study,in addition to the traditional instantaneous attribute analysis method of GPR,the polarization attribute analysis method based on Pauli decomposition and H-Alpha decomposition,similarity attribute analysis method and energy attribute analysis method are applied.The instantaneous attribute analysis method is used to reflect the stratification and physical properties of the subsurface soil;The polarization attribute analysis method is used to obtain the scattering characteristics of the LNAPL contaminant;The similarity attribute analysis method calculates the homogeneity of the medium in a small range by calculating the similarity of adjacent waveforms,thereby distinguishing the boundary of LNAPL contaminant.The energy attribute analysis is used to distinguish the diffusion center of LNAPL contaminant,which plays a guiding role in repairing of the LNAPL contaminant.