BOUNDARY RESOLUTION OF CO2 USING IR AND NIR MEASUREMENTS

Since CO2 concentrations in the boundary layer (BL) are primarily sensitive to surface fluxes mixing within the BL, closing the global carbon budget is best achieved by discriminating between CO2 in the BL from CO2 in the free troposphere. From previous studies showing that adding CO2 laser band increases sensitivity to lower troposphere and that near IR measurement (NIR) can be used to obtain “column” CO2 measurements with sufficient precision to obtain CO2 sources and sinks we used simulated retrieval approach using IR, NIR and combined radiances. In this method, jointly estimate the atmospheric temperature, water, surface temperature, emissivity and CO2 using optimal estimation provided a fully characterization of errors and sensitivity of the estimate to a simulated “true” CO2 distribution. A linear retrieval is used to examine the impact of using different spectral bands on a CO2 estimate. The results show that combined radiance retrieval i.e. using NIR and IR have the potential to resolve the boundary layer CO2 from free tropospheric CO2 and therefore to increase sensitivity to surface fluxes and to reduce transport error in inverse estimates of global carbon budget.