Development and assessment of the SMAP enhanced passive soil moisture product
Development and assessment of the SMAP enhanced passive soil moisture product
复制标题
DOI：
10.1016/j.rse.2017.08.025
复制
发表时间：
2018-01-01
影响因子：
13.5
通讯作者：
Kerr, Y.
中科院分区：
文献类型：
--
作者：
Chan, S. K.;Bindlish, R.;Kerr, Y.
美国国家航空航天局(NASA)土壤水分主动被动观测站于2015年1月发射升空，旨在每隔两到三天使用一台工作在L频段的雷达和辐射计，频繁绘制高分辨率土壤水分和冻融状态全球地图。尽管硬件故障使雷达在发射后不久就无法操作，但辐射计继续名义上运行，返回了两年多的科学数据，这些数据帮助改善了现有的水文应用程序并培育了新的应用程序。从2016年底开始，SMAP项目推出了一套新的数据产品，目的是恢复雷达故障造成的一些高分辨率观测能力的损失。这些新的数据产品包括2016年12月发布的SMAP增强被动土壤水分产品，以及2017年4月发布的SMAP/Sentinel-1主动-被动土壤水分产品。本文介绍了SMAP二级增强被动土壤水分产品(L2_SM_P_E)的开发和评估。该产品与目前的SMAP二级被动土壤水分产品(L2_SM_P)的不同之处在于，土壤水分反演发布在9公里的网格上，而不是36公里的网格上。这是通过首先将Backus-Gilbert最优内插技术应用于原始SMAP Level 1B亮度温度产品中的天线温度(T-A)数据来实现的，以利用轨道上重叠的辐射计足迹。然后，所得到的内插TA数据经过各种校正/校准程序，以成为SMAP 1C增强亮度温度乘积(L1C_TB_E)。然后，将L1C_TB_E产品张贴在9公里网格上，作为当前运行的SMAP基线土壤湿度反演算法的主要输入，以产生L2_SM_P_E作为最终输出。新产品的图像显示了标准产品中不明显的增强的视觉功能。基于代表全球不同季节和生物群的核心验证点和稀疏网络的现场数据，对2015年4月1日至2016年10月30日期间L2_SM_P_E和现场数据进行了比较。结果表明，增强型9 KM L2_SM_P与标准36 KM L2_SM_P的性能相当，其反演不确定度小于0.040 m(3)/m(3)无偏均方根误差(UbRMSE)，相关系数大于0.800。该评估还确认，在针对L2_SM_P_E实施的各种算法中，使用V-极化T-B信道的单通道算法(SCA-V)提供了最佳的检索性能，这一结果与先前针对L2_SM_P实施的评估类似。
Launched in January 2015, the National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) observatory was designed to provide frequent global mapping of high-resolution soil moisture and freeze-thaw state every two to three days using a radar and a radiometer operating at L-band frequencies. Despite a hardware mishap that rendered the radar inoperable shortly after launch, the radiometer continues to operate nominally, returning more than two years of science data that have helped to improve existing hydrological applications and foster new ones.Beginning in late 2016 the SMAP project launched a suite of new data products with the objective of recovering some high-resolution observation capability loss resulting from the radar malfunction. Among these new data products are the SMAP Enhanced Passive Soil Moisture Product that was released in December 2016, followed by the SMAP/Sentinel-1 Active-Passive Soil Moisture Product in April 2017.This article covers the development and assessment of the SMAP Level 2 Enhanced Passive Soil Moisture Product (L2_SM_P_E). The product distinguishes itself from the current SMAP Level 2 Passive Soil Moisture Product (L2_SM_P) in that the soil moisture retrieval is posted on a 9 km grid instead of a 36 km grid. This is made possible by first applying the Backus-Gilbert optimal interpolation technique to the antenna temperature (T-A) data in the original SMAP Level 1B Brightness Temperature Product to take advantage of the overlapped radiometer footprints on orbit. The resulting interpolated TA data then go through various correction/calibration procedures to become the SMAP Level 1C Enhanced Brightness Temperature Product (L1C_TB_E). The L1C_TB_E product, posted on a 9 km grid, is then used as the primary input to the current operational SMAP baseline soil moisture retrieval algorithm to produce L2_SM_P_E as the final output. Images of the new product reveal enhanced visual features that are not apparent in the standard product. Based on in situ data from core validation sites and sparse networks representing different seasons and biomes all over the world, comparisons between L2_SM_P_E and in situ data were performed for the duration of April 1, 2015-October 30, 2016. It was found that the performance of the enhanced 9 km L2_SM_P_E is equivalent to that of the standard 36 km L2_SM_P, attaining a retrieval uncertainty below 0.040 m(3)/m(3) unbiased root-mean-square error (ubRMSE) and a correlation coefficient above 0.800. This assessment also affirmed that the Single Channel Algorithm using the V-polarized T-B channel (SCA-V) delivered the best retrieval performance among the various algorithms implemented for L2_SM_P_E, a result similar to a previous assessment for L2_SM_P.