ERBE-like and ISCCP-like Outgoing Longwave Radiation from Scanner for Radiation Budget Project

The Earth's radiation budget can be directly estimated from satellite measurements of broadband (SW and LW) radiances (such as ERBE and CERES products), or indirectly calculated using the retrieved cloud and surface properties (such as ISCCP products) from satellite narrowband (VIS and IR window) measurements and other ancillary datasets. Comparison between the ERBE-retrieved and ISCCP-calculated outgoing longwave radiation (OLR) showed that, although the overall good agreement is obtained in the global/long-time scale, considerable differences exist in the regional/short-time scale. Since ScaRaB (Scanner for Radiation Budget) measures broadband and narrowband radiances simultaneously, OLR can be retrieved using ERBE algorithm with the broadband radiances or calculated using the ISCCP method with the narrowband radiances. The comparison between the ERBE-like and ISCCP-like OLR from ScaRaB is ideal to address the problem both in the ERBE radiance-to-flux conversion algorithm and in the ISCCP flux calculation (as well as ISCCP retrieval) algorithm since the time and space mismatch problem is avoided due to the simultaneous radiance measurements. Our result shows that, for the instantaneous fluxes, errors in the ERBE-retrieved values are dominated by oversimplified angular dependence models, and errors in ISCCP-calculated values arise more from the quality of the input data and uncertainties in cloud vertical structure.