Wang Likun, Chen Yong, Han Yong
Appl Opt. 2016 Sep 1;55(25):7113-9. doi: 10.1364/AO.55.007113.
Hyperspectral infrared radiance measurements from satellite sensors contain valuable information on atmospheric temperature and humidity profiles and greenhouse gases, and therefore are directly assimilated into numerical weather prediction (NWP) models as inputs for weather forecasting. However, data assimilations in current operational NWP models still mainly rely on cloud-free observations due to the challenge of simulating cloud-contaminated radiances when using hyperspectral radiances. The limited spatial coverage of the 3×3 field of views (FOVs) in one field of regard (FOR) (i.e., spatial gap among FOVs) as well as relatively large footprint size (14 km) in current Cross-track Infrared Sounder (CrIS) instruments limits the amount of clear-sky observations. This study explores the potential impacts of future CrIS FOV configuration (including FOV size and spatial coverage) on the amount of clear-sky observations by simulation experiments. The radiance measurements and cloud mask products (VCM) from the Visible Infrared Imager Radiometer Suite (VIIRS) are used to simulate CrIS clear-sky observation under different FOV configurations. The results indicate that, given the same FOV coverage (e.g., 3×3), the percentage of clear-sky FOVs and the percentage of clear-sky FORs (that contain at least one clear-sky FOV) both increase as the FOV size decreases. In particular, if the CrIS FOV size were reduced from 14 km to 7 km, the percentage of clear-sky FOVs increases from 9.02% to 13.51% and the percentage of clear-sky FORs increases from 18.24% to 27.51%. Given the same FOV size but with increasing FOV coverage in each FOR, the clear-sky FOV observations increases proportionally with the increasing sampling FOVs. Both reducing FOV size and increasing FOV coverage can result in more clear-sky FORs, which benefit data utilization of NWP data assimilation.
卫星传感器的高光谱红外辐射测量包含有关大气温度和湿度廓线以及温室气体的宝贵信息，因此被直接作为天气预报的输入数据同化到数值天气预报（NWP）模型中。然而，由于在使用高光谱辐射时模拟受云污染的辐射存在挑战，当前业务NWP模型中的数据同化仍主要依赖无云观测。当前交叉轨道红外探测仪（CrIS）仪器中一个视场区域（FOR）内3×3视场（FOV）的有限空间覆盖范围（即视场之间的空间间隙）以及相对较大的足迹尺寸（14公里）限制了晴空观测的数量。本研究通过模拟实验探讨了未来CrIS视场配置（包括视场大小和空间覆盖范围）对晴空观测数量的潜在影响。利用可见红外成像辐射计套件（VIIRS）的辐射测量和云掩膜产品（VCM）来模拟不同视场配置下的CrIS晴空观测。结果表明，在相同的视场覆盖范围（例如3×3）下，晴空视场的百分比和包含至少一个晴空视场的晴空FOR的百分比都随着视场大小的减小而增加。特别是，如果CrIS视场大小从14公里减小到7公里，晴空视场的百分比从9.02%增加到13.51%，晴空FOR的百分比从18.24%增加到27.51%。在相同的视场大小但每个FOR中的视场覆盖范围增加的情况下，晴空视场观测随着采样视场的增加而成比例增加。减小视场大小和增加视场覆盖范围都可以导致更多的晴空FOR，这有利于NWP数据同化的数据利用。
