CrIS Cloud Emission and Scattering Index (CESI)

by Xioalei Zou

CICS-MD Scientists, in collaboration with NOAA scientists, took an innovative approach for developing a cloud detection algorithm using Cross-Track Infrared Sounder (CrIS) observations.​ A set of cloud emission and scattering indices (CESI) was developed by properly pairing CrIS shortwave CO₂ channels with longwave CO₂ channels located at similar altitudes. The global distributions of CESIs derived from CrIS double CO₂ bands with weighting functions peaks located at about 321 hPa agreed well with the distributions of ice cloud optical thickness contained in the Atmospheric Infrared Sounder (AIRS) Version 6 data set (see figures below).

Figure 1: CrIS CESI at 321 hPa

Figure 2: AIRS ice cloud optical depth

The CrIS CESI cloud detection algorithm will be tested and made operationally feasible by determining some threshold values. It will play a significant role in the NOAA CrIS data assimilation system. Lin, L., X. Zou and F. Weng, 2017: Combining CrIS double CO2 bands for detecting clouds located in different vertical layers of the atmosphere. J. Geophy. Res., 122(3), 1811-1827. doi: 10.1002/2016JD025505.

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