Objective Determination of AIRS Cloud Mask using Co-Located MODIS Cloud Mask Information

Hyperspectral and multispectral infrared observations measured by the atmospheric infrared sounder (AIRS) and the moderate resolution imaging spectroradiometer (MODIS) on board earth observing system's aqua satellite provides unprecedented details of clouds, atmosphere, and surface in global scale. Both types of measurements are unique in their own ways. For example, AIRS provides spectral features that can resolve individual carbon dioxide absorption line to improve vertical resolving power for accurate temperature sounding profile. On the other hand, MODIS features multi-spectral but relative higher spatial resolution to resolve the fine spatial scale of clouds that exist in most part of our earth-atmosphere system. As a result, AIRS spectral sounding and MODIS spatial imaging capability can provide complementary global measurement information if they were synergistically utilized. High probability of cloud contamination in each of AIRS and MODIS single measurement field of view are well understood. However, accurate and objective determination of cloud or no cloud contamination (i.e. cloud mask) that requires non-static and multiple physical threshold tests based on not only the measurement condition but also its geo-location and available ancillary information. MODIS single field of view cloud mask has been developed, well tested and documented. To the contrary, AIRS cloud mask has not been studied extensively since the current official AIRS cloud clearing retrieval processing approach bypass explicit cloud detection. In this paper AIRS cloud mask is objectively determined from the accurately co-located MODIS 1-km cloud mask information within each of the AIRS field of view. The AIRS cloud mask is becoming one of the most critical initial information for any of the AIRS data utilities such as, clear radiance data assimilation, sounding retrieval, cloud property study, land and sea surface temperature retrieval, aerosol/dust detection, and spectroscopy analysis, just to name a few.