JPSS Tandem, Shortwave Infrared and Day-Night Band VIIRS Polar Winds
Presentation 1600-1630. The properties of winds from visible/near-infrared/thermal infrared satellite imagers – speed, direction, and altitude – are derived by tracking clouds in data from the Visible and Infrared Imaging Radiometer Suite (VIIRS). These Atmospheric Motion Vectors (AMVs) have shown to improve Global forecast models. However, one limitation over the polar regions is that clouds are notoriously difficult to detect and characterize with satellite imagers because of the similarities between their temperature and reflectance properties and those of the underlying snow and ice surface. Ubiquitous lower-tropospheric temperature inversions in winter and nearly isothermal temperature profiles in summer result in a very small temperature contrast between low, stratiform clouds – the most common cloud type over much of the Arctic Ocean – and the surface.
In the shortwave infrared (SWIR) portion of the spectrum the scattering properties of liquid-phase clouds and snow/ice are significantly different. Clouds are much brighter than the underlying snow or ice surface and the contrast between low clouds and the surface is large in SWIR bands around 1.6, 2.2, and 3.7 μm. This fact that has been exploited in polar cloud detection algorithms at least since the early 1990s. AVHRR, MODIS, and VIIRS all have bands at 1.6 and 3.7 μm; MODIS and VIIRS also have bands at 2.1-2.2 μm. In theory, SWIR data will provide more good features for cloud tracking and atmospheric motion vector derivation in the presence of sunlight (daytime), especially for liquid clouds over snow and ice. The VIIRS day-night band (DNB) provides another unique source of spectral information: reflected radiation at night in the presence of moonlight. Here we report on the advantages of utilizing these new spectral bands as well as tandem JPSS IR to extend the current VIIRS polar winds products.