In-Situ Measurement of Soil Permittivity at Various Depths for the Calibration and Validation of Low-Frequency SAR Soil Moisture Models by Using GPR
In-Situ Measurement of Soil Permittivity at Various Depths for the Calibration and Validation of Low-Frequency SAR Soil Moisture Models by Using GPR
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DOI：
10.3390/rs9060580
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发表时间：
2017-06
期刊：
影响因子：
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通讯作者：
C. Koyama;Hai Liu;Kazunori Takahashi;M. Shimada;Manabu Watanabe;T. Khuut;Motoyuki Sato
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文献类型：
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作者：
C. Koyama;Hai Liu;Kazunori Takahashi;M. Shimada;Manabu Watanabe;T. Khuut;Motoyuki Sato
在雷达频率低于2 GHz时，传统时域反射仪（TDR）探头土壤水分测量的5至15 cm感测深度与雷达穿透深度之间的不匹配很容易导致不可靠的原位数据。用传统方法精确定量测定不同深度的土壤含水量是繁琐的，而且通常具有很强的侵入性。提出了一种改进的方法，用于从多偏移距探地雷达（GPR）数据中估计垂直土壤水分剖面。半自动数据采集技术允许在现场进行非常快速和可靠的测量。先进的共同中点（CMP）处理，以获得定量估计的介电常数和深度的反射土壤层。该方法对TDR测量使用在不同的环境中获得的数据进行验证。深度和土壤含水量的反射层估计的均方根误差（RMSE）的顺序为5厘米和1.9体积%，分别应用所提出的技术验证合成孔径雷达（SAR）土壤湿度估计的案例研究，使用机载L波段数据和地面的P波段数据的基础上证明。对于L-波段的情况下，我们发现近地表GPR估计和扩展积分方程模型（I2 EM）的SAR检索之间的良好协议，相当于TDR获得的。在P波段，基于GPR的方法显着优于TDR方法时，使用土壤水分估计深度低于30厘米。
At radar frequencies below 2 GHz, the mismatch between the 5 to 15 cm sensing depth of classical time domain reflectometry (TDR) probe soil moisture measurements and the radar penetration depth can easily lead to unreliable in situ data. Accurate quantitative measurements of soil water contents at various depths by classical methods are cumbersome and usually highly invasive. We propose an improved method for the estimation of vertical soil moisture profiles from multi-offset ground penetrating radar (GPR) data. A semi-automated data acquisition technique allows for very fast and robust measurements in the field. Advanced common mid-point (CMP) processing is applied to obtain quantitative estimates of the permittivity and depth of the reflecting soil layers. The method is validated against TDR measurements using data acquired in different environments. Depth and soil moisture contents of the reflecting layers were estimated with root mean square errors (RMSE) on the order of 5 cm and 1.9 Vol.-%, respectively. Application of the proposed technique for the validation of synthetic aperture radar (SAR) soil moisture estimates is demonstrated based on a case study using airborne L-band data and ground-based P-band data. For the L-band case we found good agreement between the near-surface GPR estimates and extended integral equation model (I2EM) based SAR retrievals, comparable to those obtained by TDR. At the P-band, the GPR based method significantly outperformed the TDR method when using soil moisture estimates at depths below 30 cm.