Measurements of the O2 A- and B-bands for determining temperature and pressure profiles from ACE-MAESTRO:: Forward model and retrieval algorithm

The ACE-MAESTRO (Atmospheric Chemistry Experiment Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation) instrument on the SCISAT satellite is able to measure solar occultation absorption in the A- and B-bands of molecular oxygen with a spectral resolution of 2nm. Profiles of total atmospheric density are derived by exploiting the constant and known mixing ratio of O-2, and are used to determine profiles of pressure and temperature using hydrostatic balance and the ideal gas law. A highly accurate combined fast-line-by-line and extended correlated-k technique is implemented to fast forward model MAESTRO's O-2 absorption measurements, which ensures that errors in pressure and temperature resulting from the forward model approximation are essentially negligible. Estimated errors in pressure and temperature are determined for the A-, B-, and combined A-B-band retrievals for a typical retrieval, and demonstrate that pressure profiles should be derivable to within 1% and temperature to within 2 K over most altitudes using a combined A-B retrieval. The combined retrieval provides an improvement of up to 0.25% in pressure and 0.5 K in temperature over the A-band retrieval alone. The B-band could also be used alone below about 50 km, where its independent retrieval produces error estimates of 1-1.5% in pressure and 2-3 K in temperature. (c) 2007 Elsevier Ltd. All rights reserved.