Abstract
Abstract. 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.
Highlights
The survey at global scale of greenhouse gases, in particular CO2 and CH4, takes advantage of the numerous space-borne infrared instruments
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
Rodgers (2000) demonstrated that the trace of A represents the total degrees of freedom for signal (DOFSs), which indicates the amount of independent pieces of information provided by the observing system as regards as the state vector
Summary
The survey at global scale of greenhouse gases, in particular CO2 and CH4, takes advantage of the numerous space-borne infrared instruments. The TANSO-FTS (Thermal And Near infrared Sensor for carbon Observations–Fourier Transform Spectrometer) instrument, which measures simultaneously one TIR and two SWIR spectral bands with the same field of view, represents a unique resource for testing the high-resolution multispectral approach suitability. We present for the first time the contribution of high-resolution multispectral measurements for an optimal retrieval of the greenhouse gases CO2 and CH4 in clear sky conditions. We discuss the interest of using two or three spectral bands simultaneously according to the surface type and state vector composition. This synergetic approach is evaluated from the three infrared bands of the TANSO-FTS instrument thanks to a new radiative transfer algorithm developed at the Laboratoire d’Optique Atmosphérique (LOA).
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