First study of Sentinel-3 SLSTR active fire detection and FRP retrieval: Night-time algorithm enhancements and global intercomparison to MODIS and VIIRS AF products
First study of Sentinel-3 SLSTR active fire detection and FRP retrieval: Night-time algorithm enhancements and global intercomparison to MODIS and VIIRS AF products
复制标题
DOI：
10.1016/j.rse.2020.111947
复制
发表时间：
2020-10
影响因子：
13.5
通讯作者：
Weidong Xu;M. Wooster;Jiangping He;Tianran Zhang
中科院分区：
文献类型：
--
作者：
Weidong Xu;M. Wooster;Jiangping He;Tianran Zhang
海洋和陆地表面温度辐射计（SLSTR）目前在欧洲哨兵-3A和单键3B卫星上同时运行。它的观测结果预计最终将成为上午和晚上低地球轨道时段主动火（AF）探测和火辐射功率（FRP）反演的主要全球来源-目前由Terra上的中分辨率成像光谱仪（MODIS）提供的数据。在这里，我们报告的第一次发射前的哨兵-3自动对焦检测和火灾表征算法进行了重大调整，需要优化其性能与真实的SLSTR数据收集的哨兵-3A和单键3B卫星。SLSTR拥有S7“标准”和F1“火灾”通道，它们在相同的中红外（MIR）波段工作，但使用具有不同动态范围的不同探测器，并且位于不同的焦平面位置。当S7提供饱和观测时，例如在较高FRP活动火灾像素上，F1必须用于提供可靠的MIR光谱测量。然而，两个通道不同的数据特性（匹配像素的尺寸、形状和空间位置略有不同）意味着它们的测量之间的交换是不平凡的。因此，主要的算法增强是增加了专用的主动火焰像素聚类组件，需要将检测到的AF像素聚类为单独的火焰，作为该问题的解决方案。集中在夜间的数据，由于白天的实施增加的复杂性，我们比较AF信息与此更新的SLSTR算法，从近同步的MODIS Terra，我们发现，SLSTR有一个较低的最低FRP检测限，使更多的低FRP活跃火像素被识别比与MODIS的情况。当两个传感器同时检测到相同的火灾集群时，SLSTR通常测量略高的FRP，因为它能够检测到更多位于集群边缘的低FRP AF像素（匹配的SLSTR和MODIS每次火灾FRP匹配之间的OLS线性最佳拟合具有1.08的斜率）。在区域尺度上，SLSTR检测到匹配的MODIS数据包含的90%的AF像素，但也识别出额外的44%的AF像素-其中绝大多数的FRP < 5 MW。因此，来自SLSTR的区域FRP总量略高于来自MODIS的FRP总量，这些区域FRP匹配数据集之间的OLS线性最佳拟合斜率为1.10。2019年1月1°网格单元分辨率的全球火灾测绘显示，Sentinel-3B和MODIS Terra机载SLSTR的火灾模式和FRP总量非常相似，SLSTR检测到的AF像素是其7倍，但FRP总量非常相似。5°网格单元区域的案例研究显示了相同的模式，像这样的长期比较将提供将MODIS和SLSTR数据网格化为单一兼容时间序列所需的数据，用于长期趋势分析。主要基于该算法的夜间SLSTR AF产品已于2020年3月全面投入使用，并可通过近实时馈送获得。基于类似处理链的非时间关键（NTC）版本将在不久之后推出，产品可从Sentinel-3 Data Hub获得。
The Sea and Land Surface Temperature Radiometer (SLSTR) now operates concurrently onboard the European Sentinel-3A and single bond3B satellites. Its observations are expected ultimately to become the main global source of active fire (AF) detections and fire radiative power (FRP) retrievals for the mid-morning and evening low earth orbit timeslots – data currently supplied by the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard Terra. Here we report for the first-time the significant adjustments made to the pre-launch Sentinel-3 AF detection and fire characterisation algorithm required to optimize its performance with real SLSTR data collected from the Sentinel-3A and single bond3B satellites. SLSTR possesses both an S7 ‘standard’ and an F1 ‘fire’ channel that operate in the same middle infrared (MIR) waveband, but which use different detectors with differing dynamic ranges and which are located at different focal plane locations. When S7 provides saturated observations, for example over higher FRP active fire pixels, F1 must be used to provide a reliable MIR spectral measurement. However, the two channels differing data characteristics (slightly different size, shape and spatial location of the matching pixels) means that swapping between their measurements is non-trivial. The main algorithm enhancement has therefore been the addition of a dedicated active fire pixel clustering component, required to cluster the detected AF pixels into individual fires as a solution to this issue. Focusing on night-time data due to the added complexity of daytime implementation, we compare AF information derived with this updated SLSTR algorithm to that from near-simultaneous MODIS Terra, and we find that SLSTR has a lower minimum FRP detection limit which enables more lower FRP active fire pixels to be identified than is the case with MODIS. When both sensors detect the same fire cluster at the same time, SLSTR typically measures a slightly higher FRP due to it being able to detect more of the low FRP AF pixels lying at the cluster edge (the OLS linear best fit between matched SLSTR and MODIS per-fire FRP matchups has a slope of 1.08). At the regional scale, SLSTR detects 90% of the AF pixels that the matching MODIS data contains, but also identifies an additional 44% more AF pixels – the vast majority of which have FRP < 5 MW. Regional FRP totals derived from SLSTR appear slightly higher than those from MODIS because of this, and the OLS linear best fit between these regional FRP matchup datasets has a slope of 1.10. Global fire mapping at 1° grid cell resolution for January 2019 shows very similar fire patterns and FRP totals from SLSTR onboard of Sentinel-3B and MODIS Terra, with SLSTR detecting seven times more AF pixels but very similar FRP totals. Case studies in 5° grid cell areas show the same pattern, and longer-term comparisons like these will provide the data required to mesh MODIS and SLSTR data into a single compatible time-series for long-term trend analysis. The night-time SLSTR AF product based largely on this algorithm has been fully operational from March 2020 and is available from near real-time feeds. A non-time critical (NTC) version based on a similar processing chain will follow shortly after, with products available from the Sentinel-3 Data Hub.