基于探地雷达的苏打盐碱地土壤分层信息获取

    Acquiring the soil stratification of soda saline-alkali soils using ground penetrating radar

    • 摘要: 东北松嫩平原西部地区苏打盐碱地面积巨大并且改良难度大,严重制约着当地农业生产力的发展。快速了解土体中的土壤层次信息对于评价、改良与利用盐渍化土壤具有重要意义。该研究以位于吉林西部松嫩平原的典型苏打盐碱地为研究对象,利用探地雷达对不同盐碱程度的盐碱土进行野外探测,分别基于雷达图像波形图和Hilbert谱瞬时属性确定土壤分层时域位置,并采用扩展后的Dobson介电常数模型估算各层介电常数,从而获得土壤分层厚度信息,最后将两种方法检测结果与实地挖掘剖面进行对比分析。结果表明:1)土壤盐分含量对探地雷达信号的影响十分明显,大于7 ns时,电磁波幅值已很小。苏打盐碱土介电常数仍主要由实部决定,但介电常数虚部不能被忽略;2)基于雷达图像波形图和基于Hilbert谱瞬时属性两种方法均可较为准确地识别耕层(Ap)时域位置,但由于电磁波能量的衰减,基于波形图像的方法无法识别耕层以下层次,而基于Hilbert谱瞬时相位方法除个别过渡层外,可准确识别60 cm内绝大多数土壤层次;3)除个别过渡层外,基于Hilbert谱瞬时相位方法获得的土层厚度绝对误差基本在5 cm以内,相对误差在15%以内,基本能满足盐碱地野外探测需求。Hilbert谱瞬时相位对盐碱地探地雷达信号具有明显增强作用,有助于客观识别土壤分层时域位置,该研究可为快速、无损获取盐渍化土壤层次信息提供借鉴。

       

      Abstract: A large area of soda saline-alkali soil has seriously restricted the local agricultural productivity in the western Songnen Plain of Northeast China. The soil layers can also dominate the movement of water and salt in soil. It is of great significance to rapidly obtain the stratification in this area, in order to evaluate and improve the soda saline-alkali soils. Taking the typical saline-alkali soils in this area as the research object, this study aims to acquire the soil stratification using ground penetrating radar. Firstly, the soda saline-alkali soils with different salt contents were selected to conduct the ground penetrating radar (GPR) detection experiment. Then, the time domain location of stratification was then determined by radar image waveform and Hilbert spectrum instantaneous attributes. In waveform diagram of radar image, multi-point single channel waveform diagrams were combined with the radar time profiles. The soil layering was then determined as the time domain position in the overall soil layer division of the studied plot. The "three instantaneous" attributes of radar signals (instantaneous amplitude, frequency, and phase) were compared to determine the soil layering, according to Hilbert spectral instantaneous attributes. As such, the multi-point instantaneous phase maps and profiles were combined to determine the time domain position of the overall soil layer division in the studied plot. Then, the dielectric constant of each soil layer was calculated using the extended Dobson dielectric constant model. The propagation velocity of electromagnetic wave was estimated in each soil layer, according to the dielectric constant. The thickness of each soil layer was calculated to combine the time domain position of the soil layer. Finally, the field excavation profile was compared after data acquirement. The stratification of the field excavation profile was also evaluated by the soil classification experts, according to the visual and tactile characteristics of the soil. The results indicated that: 1) The content of soil salinity shared a significant impact on the ground penetrating radar signal. There was the very small amplitude of electromagnetic wave, when the two-way travel of GPR exceeded 7 ns. 2) Both radar image waveform and Hilbert spectral instantaneous attributes were accurately identified the time domain position of the plow layer (Ap). However, the waveform failed to recognize the layers below the plow layer, due to the attenuation of electromagnetic wave energy. On the contrary, the Hilbert spectral instantaneous phase was accurately identified the most soil layers within 60 cm, except for a few transition layers; 3) The absolute and relative errors of soil thickness were basically within 5 cm, and 15%, respectively, using Hilbert spectrum instantaneous phase and real soil profile. The performance was fully met the needs in the field exploration of saline-alkali land. This finding can provide a strong reference for the rapid and nondestructive access to the salinized soil layers.

       

    /

    返回文章
    返回