ASCAT IB: A radar-based vegetation optical depth retrieved from the ASCAT scatterometer satellite
ASCAT IB: A radar-based vegetation optical depth retrieved from the ASCAT scatterometer satellite
复制标题
ASCAT IB：从 ASCAT 散射仪卫星检索到的基于雷达的植被光学深度
DOI：
10.1016/j.rse.2021.112587
复制
发表时间：
2021
影响因子：
13.5
通讯作者：
Moisy Christophe
中科院分区：
文献类型：
--
作者：
Liu Xiangzhuo;Wigneron Jean-Pierre;Fan Lei;Frappart Frederic;Ciais Philippe;Baghdadi Nicolas;Zribi Mehrez;Jagdhuber Thomas;Li Xiaojun;Wang Mengjia;Bai Xiaojing;Moisy Christophe
植被光学深度（VOD）作为一种基于微波的植被水分和生物量指数，越来越多地用于研究全球气候和环境变化对植被的影响。目前，视频点播主要是从被动微波数据中提取，对主动微波数据中提取视频点播的研究较少。先进散射计（ASCAT）提供垂直-垂直（VV）偏振的长期c波段反向散射数据。本文基于水云模型（WCM）和Ulaby土壤后向散射线性模型，建立了新的ASCAT INRAE Bordeaux (IB) VOD（以下简称IB VOD）。IB VOD的主要特点是：(i)在检索中使用ERA5-Land土壤湿度（SM）数据集作为辅助SM数据集，（ii）基于像素的土壤模型参数使用随机森林（RF）进行映射，（iii）植被模型参数每天进行校准。利用2015-2019年在非洲地区采集的IB VOD产品，通过与地上生物量（AGB）、激光雷达树高（TH）、归一化植被指数（NDVI）、增强植被指数（EVI）和叶面积指数（LAI）进行对比，在空间和时间上评价其性能。结果与其他三种相同频率的VOD产品进行了相互比较。在与AGB （R= 0.92）和TH （R= 0.89）的空间相关性方面，IB VOD优于其他VOD产品，说明IB VOD具有较强的捕捉AGB和TH空间格局的能力。通过将所有VOD产品与NDVI、EVI和LAI进行比较，我们发现研究区IB VOD产品与NDVI （EVI， LAI）的时间相关性最高，分别为29.94%（36.65%,30.19%）。考虑到所有3种植被指数，与IB VOD的时间相关值最高的是落叶阔叶林、木本稀树草原和稀树草原。
Vegetation optical depth (VOD), as a microwave-based vegetation index for vegetation water and biomass content, is increasingly used to study the impact of global climate and environmental changes on vegetation. Currently, VOD is mainly retrieved from passive microwave data and few studies focused on VOD retrievals from active microwave data. The Advanced SCATterometer (ASCAT) provides long-term C-band backscatter data at Vertical-Vertical (VV) polarization. In this study, a new ASCAT INRAE Bordeaux (IB) VOD (hereafter, IB VOD), was developed based on the Water Cloud Model (WCM) coupled with the Ulaby linear model for soil backscattering. The main features of IB VOD are that (i) the ERA5-Land soil moisture (SM) dataset was used as an auxiliary SM dataset in the retrievals, (ii) pixel-based soil model parameters were mapped using Random Forest (RF), and (iii) the vegetation model parameter was calibrated for each day. The IB VOD product was retrieved over Africa during 2015–2019, and its performances were evaluated in space and time by comparing with aboveground biomass (AGB), lidar tree height (TH), normalized difference vegetation index (NDVI), enhanced vegetation index (EVI) and leaf area index (LAI). Results were inter-compared with three other VOD products at the same frequency. In terms of spatial correlation with AGB (R= 0.92) and TH (R= 0.89), IB VOD outperforms the other VOD products, suggesting IB VOD has a strong ability to capture spatial patterns of AGB and TH. By comparing all VOD products against NDVI, EVI and LAI, we found that the highest temporal correlation with NDVI (EVI, LAI) was obtained with IB VOD over 29.94% (36.65%, 30.19%) of the study region. Considering all three vegetations indices, highest temporal correlation values with IB VOD could be particularly noted for deciduous broadleaf forests, woody savannas and savannas.