Intercomparison of Carbon Monoxide Retrievals from SCIAMACHY and AIRS Nadir Observations

Abstract

Nadir observations in the near or thermal infrared channels of spaceborne spectrometers can be used to derive information on trace gases relevant for climate and air quality. In the course of the ongoing validation of the Beer InfraRed Retrieval Algorithm (BIRRA) developed for operational retrievals of carbon monoxide, methane, etc. vertical column densities from SCIAMACHY near infrared nadir observations, a new retrieval code CERVISA (Column EstimatoR Vertical Infrared Sounding of the Atmosphere) has been implemented for analysis of thermal in frared nadir observations of AIRS, TES, or IASI. Both codes share a large portion of routines, e.g., for line-by line molecular absorption and the nonlinear least squares solver. The essential difference is the part of the forward model devoted to radiative transfer through the atmosphere, i.e., Beer’s law for the near infrared with sun irradiance as source versus Schwarzschild’s equation for the thermal infrared. In this contribution, we present first results of the intercomparison of CO vertical column densities retrieved from AIRS and SCIAMACHY, including comparisons with the “official” AIRS carbon monoxide product.