Development of an Algorithm Suite for MODIS and VIIRS Cloud Climate Data Record Continuity

The launch of Suomi NPP in the fall of 2011 began the next generation of the U.S. opera-tional polar orbiting environmental observations. Similar to MODIS, the VIIRS imager provides visible through IR observations at moderate spatial resolution with a 1330 LT equatorial crossing consistent with MODIS on the Aqua platform. However, unlike MODIS, VIIRS lacks key water vapor and CO2 absorbing channels used by the MODIS cloud algorithms for high cloud detection and cloud-top property retrievals (including emissivity), as well as multilayer cloud detection. In addition, there is a significant change in the spectral location of the 2.1 μm shortwave-infrared channel used by MODIS for cloud microphysical retrievals.

The climate science community will face an interruption in the continuity of key global cloud data sets once the NASA EOS Terra and Aqua sensors cease operation. Given the instrument differences between MODIS EOS and VIIRS S-NPP/JPSS, we discuss meth-ods for merging the 14+ year MODIS observational record with VIIRS/CrIS observations in order to generate cloud climate data record continuity across the observing systems.

The first approach used by our team was to develop a cloud retrieval algorithm suite that is applied only to the common MODIS and VIIRS spectral channels. The suite uses herit-age algorithms that produce the existing MODIS cloud mask (MOD35), MODIS cloud optical and microphysical properties (MOD06), and NOAA AWG/CLAVR-x cloud-top property products. Global monthly results from this hybrid algorithm suite (referred to as MODAWG) will be shown. Collocated CALIPSO comparisons will be shown that can independently evaluate inter-instrument product consistency for a subset of the MODAWG datasets.

A second approach is to use AIRS and CrIS to generate MODIS-like CO2 and water va-por channels (albeit at coarser spatial resolution) that, in conjunction with the common imager channel set, can be used as input to the operational MODIS algorithms. Example results from this merged instrument algorithm will also be shown.