Toward Continuity in IR Absorption Radiances from HIRS and MODIS to VIIRS

This talk will discuss recent progress and issues involved with developing a continuous record of infrared (IR) absorption channel radiances since 1978, beginning with the High Resolution Infrared Radiation Sounder (HIRS), then MODIS (Moderate resolution Imaging Spectroradiometer) on the NASA Terra/Aqua platforms, and into the future from merged CrIS (Cross-track Infrared Sounder) and VIIRS (Visible Infrared Imaging Radiometers Suite) data. The HIRS and MODIS measurements include infrared (IR) radiances in the 4.5-micron carbon dioxide absorption band, the broad 6.7-micron water vapor band, and the 15-micron carbon dioxide absorption band. Among other applications, cloud top pressure/height and emissivity are derived from these channels using a technique in which the strength is with retrievals of mid-to-high clouds but less so for low clouds where there is little thermal contrast with the surface; additionally the IR absorption bands are used to infer cloud thermodynamic phase. The goal now is to extend this record from HIRS and MODIS into the Joint Polar Satellite System era. Unfortunately, VIIRS has no infrared (IR) absorption channels. Our team will demonstrate the ability to construct MODIS-like IR absorption channels for VIIRS at 750 m spatial resolution from a fusion of VIIRS and CrIS radiometric data. The method consists of two steps: (1) performing a nearest neighbor search using a k-d tree algorithm on both high spatial and low spatial resolution split-window imager radiances, and (2) averaging the convolved sounder radiances (at the lower spatial resolution of the sounder) for the nearest neighbors selected in (1) for each imager pixel. The result of the fusion process is the construction of IR absorption channel radiances at the VIIRS pixel spatial resolution of 750 m (i.e., M-band resolution). The radiometric accuracy of this approach was tested using MODIS and AIRS (Advanced Infrared Sounder) and found to be less than 1% for the carbon dioxide channels and slightly higher for the water vapor channels. The fusion radiances are now being generated operationally in forward stream at the Atmosphere SIPS (Science-led Investigator Processing System) at the University of Wisconsin-Madison. We will show fusion results for IR radiances in the carbon dioxide and water vapor channels by comparing MODIS observed and constructed radiances for these bands, and further show how the MODIS radiances compare with those derived from VIIRS and CrIS on the S-NPP platform.