Preparation of NPOESS CrIS in the Community Radiative Transfer Model (CRTM)

In conjunction with the Advanced Technology Microwave Sounder (ATMS), the Cross-track Infrared Sounder (CrIS) will provide satellite data to improve weather forecast from numerical weather prediction (NWP) models through direct assimilation of satellite radiances. In an operational NWP environment, the amounts of assimilated observed radiance are in the order of tens of thousands or more per day. The Community Radiative Transfer Model (CRTM), a fast and accurate radiative transfer (RT) model which is developed at the Joint Center for Satellite Data Assimilation (JCSDA) providing calculated radiances (or brightness temperature (BT)) and the responses of the radiances to the perturbations of state variables (radiance Jacobians, Tangent-linear (TL), and Adjoint (AD) models), is required in data assimilation and many other satellite radiance data applications.

Preliminary transmittance coefficients, which are used to calculate the channel radiances (or BTs), are ready in the CRTM for CrIS and ATMS. The ATMS sensor channel response function is using box average right now. The actual response function impact to the BT simulation is discussed in Steve Swadley's paper. The following steps are required in order to obtain the CrIS channel transmittance: Fourier transforming transmittance spectra from the Line-by-line radiative transfer model (LBLRTM)) in to the interferometric domain, apodizing the resultant interferogram with an interferometer instrument response function, and then Fourier transforming the result back into the spectral domain (channel base). The coefficients are in two formats, one is for current operational Compact OPTRAN, and the other is for a new transmittance model called Optical Depth at Pressure Space (ODPS) which additionally include trace gases coefficients.

Discussion of CrIS simulated data impacts on NCEP (National Centers for Environmental Prediction) Global Data Assimilation System (GDAS) will be presented.