ALBERT

Description: [1]  Inadequate treatment of aerosol scattering can be a significant source of error when retrieving column-averaged dry-air mole fractions of CO 2 (XCO 2 ) from space-based measurements of backscattered solar shortwave radiation. [2]  We have developed a retrieval algorithm, RemoTeC, that retrieves three aerosol parameters (amount, size, height) simultaneously with XCO 2 . Here we evaluate the ability of RemoTeC to account for light path modifications by clouds, sub-visual cirrus, and aerosols when retrieving XCO 2 from Greenhouse Gases Observing SATellite (GOSAT) TANSO-FTS measurements. We first evaluate a cloud filter based on measurements from the Cloud and Aerosol Imager and a cirrus filter that uses radiances measured by TANSO-FTS in the 2 micron spectral region, with strong water absorption. For the cloud-screened scenes, we then evaluate errors due to aerosols. We find that RemoTeC is well capable of accounting for scattering by aerosols for values of aerosol optical thickness at 750 nm up to 0.25. While no significant correlation of errors is found with albedo, correlations are found with retrieved aerosol parameters. To further improve the XCO 2 accuracy we propose and evaluate a bias correction scheme. [3]  Measurements from twelve ground-based stations of the Total Carbon Column Observing Network (TCCON) are used as a reference in this study. We show that spatial co-location criteria may be relaxed using additional constraints based on modeled XCO 2 gradients, to increase the size and diversity of validation data and provide a more robust evaluation of GOSAT retrievals. Global-scale validation of satellite data remains challenging and would be improved by increasing TCCON coverage.