The NOAA Unique CrIS/ATMS processing System (NUCAPS): algorithm description and validation results after two years in orbit

We present an overview of the main characteristics of the NOAA Unique CrIS/ATMS processing System (NUCAPS) Environmental Data Records (EDRs). Primary focus of this study is to determine the information content and the accuracy of the retrieved hydrological and trace gas variables. Furthermore, we assess the level of inter-consistency and homogeneity with respect to current operational hyper spectral EDRs from the Atmospheric InfraRed Sounder (AIRS) and the Infrared Atmospheric Sounding Interferometer (IASI). Since February 2013, NOAA/NESDIS/OSPO has been running three hyper spectral sounding product processing systems: 1) the Atmospheric InfraRed Sounder/Advanced Microwave Sounding Unit (AIRS/AMSU) retrieval product processing system, which has been running in near-real time since 2002; 2) the Infrared Atmospheric Sounder Interferometer/ Advanced Microwave Sounding Unit/Microwave Humidity Sounder (IASI/AMSU/MHS) NOAA unique cloud-cleared radiances and trace gas product processing system, which has been running operationally since 2008; and 3) the Cross-track Infrared Sounder/ Advanced Technology Microwave Sounder (CrIS/ATMS) NOAA unique cloud-cleared radiances and trace gas product processing system, which will become operational in the Fall of 2013. The long term strategy of NOAA/NESDIS will also involve the operational processing of the future JPSS and MetOp II and III missions, spanning a total period of ~30 years of hyper spectral remote sounding data processing. The NOAA/NESDIS/STAR processing system is a modular architecture that was specifically designed to be compatible with multiple instruments: the same retrieval algorithm and the same underlying spectroscopy are currently used to process AIRS, IASI and CrIS data. This property is of fundamental importance in guaranteeing homogeneity across the multi-platform integrated dataset of retrieved Environmental Climate Variables. Separate studies have also validated the radiance homogeneity of the existing AIRS and IASI sounders [L. Strow, 2008]. The CrIS instrument was launched in October 2011 and will ensure the continuity of the afternoon orbit sounding for the next decade. The ongoing overlapping period will guarantee the inter-calibration between the three instruments. The combined sounding geometry of these three hyper spectral instruments (AIRS and CrIS have a 1:30pm equator crossing time; IASI has a 9:30 am equator crossing time) and the employment of the same retrieval methodology will provide an unprecedented uniform and long-term integrated database of six global atmospheric measurements per day.

The robustness of this algorithm has been demonstrated by a large number of validation efforts. Comparisons with respect to co-located radiosondes [Divakarla et al., 2006; D. Tobin et al., 2005], re-analyses and other existing retrieval techniques [Tony Reale, 2010; http://www.star.nesdis.noaa.gov/smcd/opdb/poes/ ] have demonstrated a high level of stability in NUCAPS Fundamental Climate Data Records and a robust accuracy in the derived Environmental Climate Variables. Particular effort has been devoted to the validation of the retrieved hydrological variables such as cloud pressure, cloud fraction, temperature profiles, water vapor profiles and total precipitable water. These variables are shown to successfully meet the GCOS accuracy requirements for climate applications [http://gosic.org/ios/GCOS-main-page.htm].

The NOAA/NESDIS/STAR hydrological and trace gas data set will be presented and we encourage feedbacks from the product users' community.