Methane Retrievals in the Thermal and Shortwave Infrared from IASI
Abstract
RAL has developed an optimal estimation scheme to retrieve height resolved information on CH4 from IASI measurements in the thermal infrared (TIR) 7.9 μm band. This scheme has been extensively validated in the context of UK national (NERC/NCEO) and EUMETSAT funded projects and shown to perform well in comparison with column averages from both ground-based observations and the shortwave sounder GOSAT [1]. The scheme extracts two independent pieces of information on the profile, with sensitivity extending into the lower troposphere. Column-averaged mixing ratios with a precision of 20-40 ppbv can be derived, however sensitivity to the boundary layer is weak compared to shortwave sounders (and dependent on atmospheric/surface state).IASI also measures methane lines in the 3.7 μm spectral range, where there is a significant solar contribution to measurements in the day-time over land, increasing sensitivity to methane in the boundary layer. However, this spectral range has not yet been exploited due to the complexity of modelling both solar and thermal contributions to the measurements and the relatively low signal to noise ratio of IASI in this spectral region. In this paper we will summarise the performance of the TIR scheme and go on to present initial findings from an investigation into the potential of adding information on near-surface methane by exploiting the 3.7 μm band.
- Publication:
-
ATMOS 2015
- Pub Date:
- November 2015
- Bibcode:
- 2015ESASP.735E...3K