The Remote-Sensing Group has developed an optimal estimation scheme to retrieve global height-resolved methane distributions from measurements in the thermal infrared (7.9 micron) band of the Infrared Atmospheric Sounding Interferometer (IASI). Using data from IASI, methane retrievals can be performed at relatively high spatial resolution, both day and night, over land and ocean.
The retrieval scheme extracts two independent pieces of information on the profile, with sensitivity extending into the lower troposphere. Column averaged volume mixing ratios derived from the retrieved profile have a precision of 20 – 40 ppbv, and agree well with those from both the ground-based Total Column Carbon Observing Network (TCCON) and the University of Leicester's retrievals from the satellite shortwave infrared (SWIR) sounder GOSAT. A plot of global monthly averaged, column average methane retrieved from the RAL IASI methane scheme can be seen in Figure 1.
Exploiting the JASMIN-CEMS infrastructure at RAL, the full IASI MetOp-A mission to date (2007-2015) has been processed, producing the IASI MetOp-A TIR Methane v1.0 dataset which is available from the Centre for Environmental Data Analysis (CEDA). As well as being used to perform offline processing, the methane processor has also been incorporated into the RSG MetOp near real-time (NRT) chain, providing methane retrievals within a few hours of the IASI measurements being made.
In addition to the TIR retrieval scheme, work to develop a short-wave infrared (SWIR) methane retrieval using IASI's 3.7 micron band is currently underway. Exploiting methane lines in the SWIR spectral region has the potential to increase IASI's sensitivity to methane in the boundary layer through the contribution from surface-reflected solar radiation.
If you are interested in acquiring our data, or would like help using it, please contact Dr Richard Siddans or Dr Diane Knappett.
For more information please contact: RAL Space Enquiries