Relationship Between Active and Passive Microwave Signals Over Vegetated Surfaces
Relationship Between Active and Passive Microwave Signals Over Vegetated Surfaces
复制标题
植被表面的主动和被动微波信号之间的关系
DOI：
10.1109/tgrs.2021.3053586
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发表时间：
2022
影响因子：
8.2
通讯作者：
M. Link;T. Jagdhuber;P. Ferrazzoli;L. Guerriero;D. Entekhabi
中科院分区：
文献类型：
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作者：
M. Link;T. Jagdhuber;P. Ferrazzoli;L. Guerriero;D. Entekhabi
美国航天局土壤湿度主动被动（SMAP）卫星使命的目的是通过将同时但多分辨率的L波段主动和被动微波测量结合起来，产生分辨率更高的表层土壤湿度产品。由于SMAP雷达在使命初期停止运行，因此在合并产品中使用了哥白尼哨兵1号C波段雷达观测。这种协同作用建立在两个基本基础上：第一，主动和被动信号以已知和系统的方式协变，第二，测量可以在多个分辨率下进行。在这项研究中，我们进行数值模拟和评估全球卫星观测，以测试第一个基础（协变）。具体的重点在于调节主动-被动关系的植被冠层的作用。我们使用离散辐射传输模型来模拟主动信号和被动信号之间关系的斜率β和决定系数R²，考虑了三种植被类型，该模型在之前的实验研究中已对其进行了广泛评估。我们发现，后向散射和发射率之间的线性关系可以建立在一个范围内的植被条件。有源和无源信号之间的耦合随着植被含水量的增加而降低，因此，对于L波段/L波段配置，在4 kg/m²（6.3 kg/m²）和1.5 kg/m²（2 kg/m²）的范围内保持中等或更高的相关性（非零斜率）。我们分解不同的土壤-植被散射机制，如双反弹，和不同的测量误差水平的主被动关系的影响。与卫星数据的比较证实，我们的模拟捕捉到的幅度和主要趋势，发现在全球植被的土地块。
The NASA Soil Moisture Active Passive (SMAP) satellite mission aims to produce enhanced resolution surface soil moisture products by combining coincident but multiresolution L-band active and passive microwave measurements. Since the SMAP radar ceased operations early in the mission, Copernicus Sentinel-1 C-band radar observations are used in the combined product. The synergy is built on two basic foundations: first, active and passive signals covary in a known and systematic fashion, and second, measurements are available at multiple resolutions. In this study, we perform numerical simulations and assess global satellite observations to test the first foundation (covariation). Specific focus lies on the role of the vegetation canopy in modulating the active-passive relationship. We use a discrete radiative transfer model to simulate the slope β and coefficient of determination R² of the relationship between active and passive signals, considering three vegetation types for which the model has been extensively assessed in previous experimental studies. We find that a linear relationship between backscatter and emissivity can be established over a range of vegetation conditions. The coupling between active and passive signals decreases with increasing vegetation water content, such that moderate or higher correlations (nonzero slopes) are retained up to 4 kg/m² (6.3 kg/m²) for L-band/L-band and 1.5 kg/m² (2 kg/m²) for the C-band/L-band configuration. We decompose the effects of different soil-vegetation scattering mechanisms, such as double-bounce, and different measurement error levels on the active-passive relationship. Comparisons with satellite data confirm that our simulations capture magnitudes and major trends found across global vegetated land masses.