|Paper title||Global methane retrievals from IASI|
|Form of presentation||Poster|
The RAL Remote Sensing Group has developed an optimal estimation scheme to retrieve global height-resolved information on methane from IASI using the 7.9 µm band. This scheme uses pre-retrieved temperature, water vapour and surface spectral emissivity from the RAL Infrared Microwave Sounder (IMS) retrieval scheme, based on collocated data from IASI, MHS and AMSU. The IASI methane retrieval scheme has been used to reprocess the IASI MetOp-A record, producing a global 10-year v2.0 dataset (2007-17) (http://dx.doi.org/10.5285/f717a8ea622f495397f4e76f777349d1) and has also been applied to IASI on MetOp-B to extend the record to 2021.
While providing information on two independent vertical layers in the troposphere, sensitivity in the 7.9 µm band decreases towards the ground, due to decreasing thermal contrast between the atmosphere and surface. A combined scheme exploiting the high signal-to-noise information from Sentinel-5P (SWIR/column) with that from IASI MetOp-B (TIR/height-resolved) would enable lower tropospheric distributions of methane to be resolved. Lower tropospheric concentrations are more closely related to emission sources than are column measurements and inverse modelling of surface fluxes should be less sensitive to errors in representation of transport at higher altitudes; a limiting factor for current schemes.
Here we present findings from the IASI methane v2.0 dataset and introduce the RAL SWIR-TIR scheme, which combines Level 2 products from Sentinel 5P and IASI/CrIS to resolve lower tropospheric methane and carbon monoxide.