The analysis of soil and land cover scattering properties and their connection with the parameters of microwave scattering is a longstanding research topic. Recently, the advent of modern space-borne microwave radiometers like SMAP in addition to the trend towards open data for scientific use fostered the development of enhanced models based on data fusion from different platforms permitting more accurate assessments. SMAP was designed to operate on an integrated combination of a radiometer and a radar, both operating in L-band. Unexpected failure of the radar component encouraged scientists to experiment various combination of data from the surviving radiometer with other sources of radar data, notably C-band Sentinel-1 data. In this work, we present a case study on a possible combination of SMAP radiometer data with X-band radar data from TerraSAR-X and COSMO-SkyMed, comparing results with those provided by NASA from their standard production procedures. The study was performed on two test sites, one at an agricultural site in Germany and one in the Brazilian Amazon, to explore very different vegetation conditions. This work is a part of a broader research effort addressing the combination of multiple sources of passive and active microwave sensing data. The research question defining this research effort is whether the use of data from multiple active sources affords either obtaining more accurate estimates of active–passive co-variation parameters for a given observation period, or shortening the minimum observation period by increasing the temporal density of active samples. In this framework, this paper addresses a preliminary comparison of fresh and past results obtained from C-, X-, and L-band active sensing data. The observed relations offer interesting clues on the impact of band selection on soil vegetation analysis.

中文翻译：

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植被表面上被动-主动微波测量的协变：以L波段无源以及L波段，C波段和X波段有源为例

分析土壤和土地覆盖物的散射特性及其与微波散射参数的关系是一个长期的研究课题。近来，像SMAP这样的现代星载微波辐射计的出现，除了向科学使用开放数据的趋势外，还促进了基于来自不同平台的数据融合的增强模型的开发，从而可以进行更准确的评估。SMAP设计为在辐射计和雷达的集成组合中运行，两者均在L波段运行。雷达组件的意外故障促使科学家尝试将幸存的辐射计的数据与其他雷达数据源（尤其是C波段Sentinel-1数据）进行各种组合。在这项工作中，我们将结合SMAP辐射计数据与TerraSAR-X和COSMO-SkyMed的X波段雷达数据的可能组合，进行案例研究，并将结果与​​NASA从其标准生产程序中获得的结果进行比较。这项研究是在两个测试地点进行的，一个在德国的一个农业地点，另一个在巴西的亚马逊河地区，以探索非常不同的植被条件。这项工作是更广泛的研究工作的一部分，致力于研究无源和有源微波感测数据的多种来源的组合。定义这项研究工作的研究问题是，使用来自多个主动源的数据是否能够在给定的观察周期内获得更准确的主动-被动协变量参数估计，还是通过增加主动源的时间密度来缩短最小观察周期？样品。在此框架下，本文致力于对从C波段，X波段和L波段有源传感数据获得的最新结果与过去结果进行初步比较。观察到的关系为频带选择对土壤植被分析的影响提供了有趣的线索。