Synergetic SWIR/TIR Retrieval of CH4 with GOSAT/TANSO-FTS Data.
De Wachter, Evelyn; Kumps, Nicolas; Vandaele, Ann Carine; Kochenova, Svetlana; Vandenbussche, Sophie; De Mazière, Martine
Belgian Institute for Space Aeronomy (BIRA-IASB), BELGIUM

Methane (CH4), being the second most important greenhouse gas, is produced at the surface by both natural (wetlands, termites, geological sources) and anthropogenic (rice agriculture, ruminants, mining...) processes. Despite the recognised importance of an accurate understanding of the CH4 budget there are still gaps in our knowledge of its sources and sinks. Global observations of CH4 with a high sensitivity to its near-surface concentrations will help to improve our knowlegde.
In this context, the ESA SIROCCO ("Synergetic SWIR and IR retrievals of near-surface concentrations of CH4 and CO for Earth and Planetary Atmospheres") project aims at retrieving the near-surface concentrations of CH4 and CO by combining shortwave infrared (SWIR) and thermal infrared (TIR) passive remote sensing measurements in a synergetic way. The TANSO-FTS instrument onboard GOSAT, being an ESA Third Party mission, is the first instrument that covers both the SWIR (CH4) and TIR (CH4) spectral regions. In this work we will present first results of a synergetic SWIR/TIR retrieval of CH4 from TANSO-FTS spectra with the ASIMUT radiative transfer and retrieval code developed at IASB-BIRA. This code was recently coupled to the (V)LIDORT forward model package in order to include the complete treatment of scattering effects into the radiative transfer calculations.
We will discuss the characteristics and performance of the retrieval test case with a specific focus on how to increase the vertical information content of CH4. With this work we want to better exploit the available data to provide information on CH4 as close as possible to its associated sources, and thereby provide a better understanding and quantification of its budget.