Surface pressure estimates from satellite data in the oxygen A‐band: Applications to the MOS sensor over land

A fast method for the Apparent Pressure Retrieval (APR method) over land from satellite data, based on a two band ratio in the oxygen A-band (759-770 nm), is described. This method is devoted to the cloud detection and atmospheric corrections. Parameterizations are performed from line-by-line calculations assuming a pure absorbing medium. Moreover, we defined a corrective factor to account for scattering effects of the atmosphere. We validated this method with measurements of the MOS sensor (Modular Optoelectronic Scanner), whose spectral characteristics are appropriate. Comparisons with ECMWF (European Centre for Medium-Range Weather Forecasts) pressures showed the need to perform in-flight calibrations over a reference scene to account for spectral shifts of filter responses. Therefore we selected bright surfaces for the calibration, such as deserts, because of their major contribution to the satellite signal. After calibration the accuracy of the method is about 10 hPa over bright surfaces. Comparisons for various meteorological and geographical conditions showed that deviations between ECMWF pressures and MOS apparent pressures are generally less than 30 hPa using scattering corrections. These deviations are multiplied by 2 without correction. The APR method has been included in the cloud detection and atmospheric correction algorithms for the MOS data processing over land. Theoretical studies showed that the APR method is suitable for the cloud discrimination and that an error of 30 hPa on the surface pressure retrieval has no noticeable effect on the geophysical products of these algorithms, such as aerosol optical thickness or surface reflectance. Consequently, this method is potentially applicable to the retrieval of the apparent pressure over land with the MOS algorithms, as well as other similar satellite sensors such as the Medium Resolution Imaging Spectrometer.