Generation and use of Proxy CrIS and ATMS Data

CrIS and ATMS comprise the advanced IR/MW temperature sounding system that will first fly on NPP and then NPOESS. CrIS and ATMS have spectral and noise characteristics that are similar to those of AIRS, AMSU-A, and HSB currently flying on EOS Aqua. NGST will be generating temperature and moisture profile EDR's derived from CrIS/ATMS observations using a retrieval algorithm developed by AER and optimized based on simulated CrIS/ATMS observations. This approach can mask limitations of a retrieval algorithm, optimized using simulated observations, that will show up when used with real CrIS/ATMS observations that are affected by real clouds, surface spectral emissivity, non-local thermodynamic equilibrium, sub-pixel variability, perfect radiative transfer physics (as opposed to the approximations made when analyzing the data), etc. In order to test the performance of the NGST CrIS/ATMS retrieval algorithm on "real" observations, we have generated proxy CrIS/ATMS observations derived from actual AIRS/AMSU/HSB observations using a new methodology which expresses the proxy radiances as a linear combination of the actual AIRS/AMSU observations. This proxy data will contain the effects of all the factors listed above. Proxy AIRS/AMSU observations were also generated based on actual AIRS/AMSU observations using the same methodology and shown to agree with actual observations up to instrumental noise. The new methodology to generate proxy data from observed observations of a different (or the same) closely related instrument will be described. Also shown will be retrieval results based on real AIRS/AMSU observations, proxy AIRS/AMSU observations, and proxy CrIS/ATMS observations.