Multispectral information from TANSO-FTS instrument – Part 1: Application to greenhouse gases (CO<sub>2</sub> and CH<sub>4</sub>) in clear sky conditions

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 CO 2 and CH 4 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 CO 2 and CH 4 . 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 CO 2 and CH 4 simultaneously with a similar accuracy to using all channels together to retrieve each gas separately.

Satellite observations of atmospheric methane and their value for quantifying methane emissions

“…Multispectral retrievals in the SWIR and TIR combine the advantages of both approaches and provide some vertical profile information, as demonstrated by Herbin et al (2013) using the combination of SWIR and TIR data from GOSAT, and by Worden et al (2015) using the combination of SWIR from GOSAT and TIR from TES. This could enable separation between the local/regional methane enhancement near the surface and the higher-altitude methane background (Bousserez et al, 2015).…”

Multispectral information from TANSO-FTS instrument – Part 2: Application to aerosol effect on greenhouse gas retrievals

“…To be consistent with the first paper (Herbin et al, 2013), the a priori error covariance matrix S a is assumed diagonal with the ith diagonal element (S a,ii ) defined as…”

“…1, are computed from our forward model with refractive index coming from Sutherland and Khanna (1991) for biomass particles, and from Volz (1973) for sand dust, assuming a bi-modal lognormal distribution and an aerosol optical depth (AOD) of τ (440 nm) = 0.55 and τ (1020 nm) = 0.25, respectively. As stated in the first paper (Herbin et al, 2013), two matrices (A and S x ) allow a full characterization of the information provided by the observing system. A, which is the averaging kernel matrix, gives a measure of the sensitivity of the retrieved state to the true state, and is defined by…”

“…Since this paper is the second in a series describing the effects of spectral synergy on the atmospheric observations, the basic specifications of the Greenhouse gases Observing SATellite (GOSAT) instrument (Kuze et al, 2009) and the theoretical bases of the information content were outlined already in Part 1 (Herbin et al, 2013) and are not recalled here. Therefore, the paper is organized as follows: Sect.…”

“…The aerosol layer parameters are assumed to be known from ancillary data and are treated as nonretrieved parameters, but they are explicitly taken into account in the forward model. To be consistent with the first part of the study (Herbin et al, 2013), the IC analysis is based on the 694 most informative channels representative of the desert and ocean surfaces selected from a channel selection procedure in clear sky conditions. In this particular case, the model parameter error covariance matrix (S f ) has to be updated with uncertainties on aerosol parameters in order to understand the impact of aerosol parameters on the error budget and information content of gas column concentration.…”