Comparing Cross-track Infrared Sounder Observations with Forward Model Calculations

Abstract:

As part of ongoing calibration and validation efforts for the Cross-track Infrared Sounder (CrIS), we have developed a framework for running forward model calculations based on interpolated reanalysis data products from numerical weather prediction centers. These forward calculations can then be compared to the observations to check for bias errors or artifacts. The framework has a flexible design which allows for multiple forward models to be run. It will support a variety of studies, for example comparisons with high accuracy reference forward models on selected subsets, or comparisons with faster approximate models on more extensive data sets. These studies can help characterize sensor biases as well as differences between radiative transfer models. Initial results using the reference line-by-line model LBLRTM, from Atmospheric and Environmental Research, reveal small biases in the CrIS measurements that are dependent on both the detector and interferometer sweep direction. Updated calibration algorithms applied to the raw CrIS data are then tested within the framework to determine the best way to reduce the bias errors. This work is expected to lead to improvements in the radiative transfer modeling of the CrIS instrument line shape needed for accurate assimilation of the CrIS full resolution radiance spectra.