Measurements of the [formula omitted][formula omitted]- and [formula omitted]-bands for determining temperature and pressure profiles from ACE–MAESTRO: Forward model and retrieval algorithm

Abstract

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 2 nm. 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.