A Rapid Cloud Mask Algorithm for Suomi NPP VIIRS Imagery EDRs A33M-0334 1378159 1378160 A cloud mask algorithm, based on a Landsat 7 automatic cloud cover assessment, has been developed for use with Suomi National Polar-orbiting Partnership (NPP) Visible Infrared Imager Radiometer Suite (VIIRS) Imagery Environmental Data Records (EDRs). The algorithm consists of a sequence of pixel-based tests that use thresholds on, or combinations of, VIIRS top-of-atmosphere reflectances and brightness temperatures. Each test returns a binary (clear or cloudy) result. For a pixel to be classified as cloudy, it must pass all tests. The similarity between the visible, near-infrared, mid-infrared and thermal bands of ETM+ and the VIIRS imager made the adaptation of the Landsat 7 algorithm to VIIRS possible. This cloud mask algorithm provides a simpler, though less informative and robust, alternative to the VIIRS Cloud Mask (VCM) Intermediate Product, with the advantage in that it can be applied to a VIIRS Imagery EDR to conveniently quantify the fractional cloud cover in the scene or in a spatial subset. Several comparisons are shown between the product of this algorithm and the VCM, with preliminary results indicating a good match between the two. A consistent failure of the current algorithm occurs in scenes containing snow: the original Landsat 7 algorithm uses ETM+ band 2 (0.53-0.61 ┬Ám), which isn’t present in the VIIRS Imagery product, in computing a normalized snow difference index that helps separate snowy from cloudy pixels. Ongoing research will investigate directly implementing the VIIRS Normalized Difference Snow Index algorithm to identify snowy pixels.
Mark Piper Exelis Visual Information Solutions, Boulder, CO, USA