Multispectral information from TANSO-FTS instrument – Part 1: Application to greenhouse gases (CO2 and CH4) in clear sky conditions

The Greenhouse gases Observing SATellite (GOSAT) mission, and in particular the Thermal And Near infrared Sensor for carbon Observations–Fourier Transform Spectrometer (TANSO-FTS) instrument, has the advantage of being able to measure simultaneously the same field of view in different spectral ranges with a high spectral resolution. These features allow studying the benefits of using multispectral measurements to improve the CO2 and CH4 retrievals. In order to quantify the impact of the spectral synergy on the retrieval accuracy, we performed an information content (IC) analysis from simulated spectra corresponding to the three infrared bands of TANSO-FTS. The advantages and limitations of using thermal and shortwave infrared simultaneously are discussed according to surface type and state vector composition. The IC is then used to determine the most informative spectral channels for the simultaneous retrieval of CO2 and CH4. The results show that a channel selection spanning the three infrared bands can improve the computation time and retrieval accuracy. Therefore, a selection of less than 700 channels from the thermal infrared (TIR) and shortwave infrared (SWIR) bands allows retrieving CO2 and CH4 simultaneously with a similar accuracy to using all channels together to retrieve each gas separately.