Utilizing calibrated GPS reflected signals to estimate soil reflectivity and dielectric constant: Results from SMEX02
Utilizing calibrated GPS reflected signals to estimate soil reflectivity and dielectric constant: Results from SMEX02
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DOI：
10.1016/j.rse.2005.09.015
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发表时间：
2006-01-15
影响因子：
13.5
通讯作者：
Masters, D
中科院分区：
文献类型：
--
作者：
Katzberg, SJ;Torres, O;Masters, D
广泛的反射GPS数据收集使用的GPS反射计安装在HC 130飞机在土壤水分实验2002年（SMEX 02）附近的艾姆斯，爱荷华州。与此同时，还获得了广泛的地面实况数据，包括点土壤水分剖面、近地表土壤水分区域采样、总绿色生物量和降水历史等。以前，没有报道过校准在陆地上获得的反射GPS数据集的努力。本文报告的结果，两种方法来校准的数据，产生一致的结果。它示出，估计反射信号的强度，通过（1）假设近似镜面反射或（2）推断表面斜率概率密度和相关的归一化常数给出基本上相同的结果，在SMEX 02中遇到的条件。校正后的数据被转换为表面反射率，然后介电常数作为校准方法的测试。利用广泛的原位土壤水分相关的数据，本文还提出了比较GPS推断的相对介电常数与Wang-Schmugge模型经常使用的体积含水量介电常数。结果表明，校准的GPS反射率估计遵循预期的依赖性介电常数与体积水分，但具有以下资格：土壤湿度值的反射率似乎来自只有顶部1-2厘米的土壤，结果与其他微波技术在L波段工作的结果一致。然而，实验得出的介电常数一般低于预测。提出了可能的解释来解释这一结果。(C)2005年爱思唯尔公司All rights reserved.
Extensive reflected GPS data was collected using a GPS reflectometer installed on an HC130 aircraft during the Soil Moisture Experiment 2002 (SMEX02) near Ames, Iowa. At the same time, widespread surface truth data was acquired in the form of point soil moisture profiles, areal sampling of near-surface soil moisture, total green biomass and precipitation history, among others. Previously, there have been no reported efforts to calibrate reflected GPS data sets acquired over land. This paper reports the results of two approaches to calibration of the data that yield consistent results. It is shown that estimating the strength of the reflected signals by either (1) assuming an approximately specular surface reflection or (2) inferring the surface slope probability density and associated normalization constants give essentially the same results for the conditions encountered in SMEX02. The corrected data is converted to surface reflectivity and then to dielectric constant as a test of the calibration approaches. Utilizing the extensive in-situ soil moisture related data this paper also presents the results of comparing the GPS-inferred relative dielectric constant with the Wang-Schmugge model frequently used to relate volume moisture content to dielectric constant. It is shown that the calibrated GPS reflectivity estimates follow the expected dependence of permittivity with volume moisture, but with the following qualification: The soil moisture value governing the reflectivity appears to come from only the top 1-2 cm of soil, a result consistent with results found for other microwave techniques operating at L-band. Nevertheless, the experimentally derived dielectric constant is generally lower than predicted. Possible explanations are presented to explain this result. (C) 2005 Elsevier Inc. All rights reserved.