Using CALIPSO to explore the sensitivity to cirrus height in the infrared observations from NPOESS/VIIRS and GOES-R/ABI

This paper demonstrates how the availability of specific infrared channels impacts the ability of two future meteorological satellite imagers to estimate cloud-top pressure. Both of the imagers are planned for launch by the United States, one for a geostationary platform and the other for a polar-orbiting platform. The geostationary imager, the Advanced Baseline Imager (ABI), will be flown first on the GOES-R platform. In addition to the split window channels at 11 and 12 μm, it has one spectral channel located at 13.3 μm where there is relatively strong absorption of H2O and CO2. The polar-orbiting imager, called the Visible/Infrared Imager Radiometer Suite (VIIRS) and flown on the National Polar-Orbiting Environmental satellite Suite (NPOESS), has spectral channels in window regions only. The lack of an absorbing channel on VIIRS is shown to have negative consequences for the inference of cloud-top pressure. This paper investigates the impact on the ability of a satellite imager such as VIIRS to confidently estimate cloud-top pressure due to the absence of infrared absorption channels. The solution space is defined as the depth of the atmospheric layer in which a cloud can be placed where the calculated top-of-atmosphere radiances match the measurements used in the cloud-top pressure retrieval. For optically thin cirrus, the channels used by the operational VIIRS algorithm provide a solution space of over 200 hPa. However, the inclusion of the single CO2 channel at 13.3 μm on the ABI narrows the solution space to under 30 hPa. Our imager-based analysis is performed using Moderate Resolution Imaging Spectroradiometer (MODIS) data, which provides the relevant channel information with sufficient spatial resolution and radiometric accuracy. Additional results are provided using data from the current GOES and POES imagers. Active lidar data from Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation/Cloud-Aerosol Lidar with Orthogonal Polarization (CALIPSO/CALIOP) observations are used to provide cloud boundaries for verification.