Satellite observation of atmospheric methane: intercomparison between AIRS and GOSAT TANSO-FTS retrievals

Abstract

Abstract. Space-borne observations of atmospheric methane (CH 4 ) have been made using the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua satellite since August 2002 and the Thermal and Near-infrared Sensor for Carbon Observation Fourier Transform Spectrometer (TANSO-FTS) on the Greenhouse Gases Observing Satellite (GOSAT) since April 2009. This study compared the GOSAT TANSO-FTS thermal infrared (TIR) version 1.0 CH 4 product with the collocated AIRS version 6 CH 4 product using data from 1 August 2010 to 30 June 2012, including the CH 4 mixing ratios and the total column amounts. The results show that at 300-600 hPa, where both AIRS and GOSAT-TIR CH 4 have peak sensitivities, they agree very well, but GOSAT-TIR retrievals tend to be higher than AIRS in layer 200-300 hPa. At 300 hPa the CH 4 mixing ratio from GOSAT-TIR is, on average, 10.3 ± 31.8 ppbv higher than that from AIRS, and at 600 hPa GOSAT-TIR retrieved CH 4 is −16.2 ± 25.7 ppbv lower than AIRS CH 4 . Comparison of the total column amount of CH 4 shows that GOSAT-TIR agrees with AIRS to within 1 % in the mid-latitude regions of the Southern Hemisphere and in the tropics. In the mid to high latitudes in the Northern Hemisphere, comparison shows that GOSAT-TIR is ∼ 1-2 % lower than AIRS, and in the high-latitude regions of the Southern Hemisphere the difference of GOSAT from AIRS varies from −3 % in October to +2 % in July. The difference between AIRS and GOSAT TANSO-FTS retrievals is mainly due to the difference in retrieval algorithms and instruments themselves, and the larger difference in the highlatitude regions is associated with the low information content and small degrees of freedom of the retrieval. The degrees of freedom of GOSAT-TIR retrievals are lower than that of AIRS, which also indicates that the constraint in GOSAT-TIR retrievals may be too strong. From the good correlation between AIRS and GOSAT-TIR retrievals and the seasonal variation they observed, we are confident that the thermal infrared measurements from AIRS and GOSAT-TIR can provide valuable information to capture the spatial and temporal variation of CH 4 , especially in the mid-upper troposphere, in most periods and regions.

Methane profiles from GOSAT thermal infrared spectra

“…In these studies, the degrees of freedom for signal (DOFS) of the retrieval is significantly lower than 1. Moreover, Zou et al (2016) compared the retrieval of methane profiles from GOSAT and AIRS thermal infrared measurements and observed a prevalent bias at 9 km altitude of about +3 % between both satellite retrievals (AIRS minus GOSAT).…”

“…Currently five nadir-viewing instruments in the thermal infrared are operational on satellite platforms; Atmospheric InfraRed Sounder3816 A. de Lange and J. Landgraf: CH 4 profiles from GOSAT-TIR spectra 2008; Zou et al, 2016); Tropospheric Emission Spectrometer (TES), aboard AURA, launched in 2004 Worden et al, 2012Worden et al, , 2015; Infrared Atmospheric Sounding Interferometer (IASI), aboard Metop-A and Metop-B, launched in respectively 2006 and 2012 (Razavi et al, 2009;Crevoisier et al, 2013;Cressot et al, 2014;Siddans et al, 2017); Thermal and Near infrared Sensor for Carbon Observation -Fourier Transform Spectrometer (TANSO-FTS) aboard the Japanese Greenhouse Gases Observing Satellite (GOSAT), launched in 2009; Cross-track Infrared Sounder (CrIS), aboard Suomi-NPP, launched in 2011 (Han et al, 2013). Furthermore, GOSAT-2, the successor of the GOSAT satellite, will also be equipped with two thermal infrared bands (together covering the same wavelength range as the one TIR band in GOSAT) and a new generation of IASI spectrometers (IASI-NG) will fly on three successive Metop-SG A satellites of the European Organisation for the Exploitation of Meterological Satellites (EUMETSAT) Polar System of Second Generation (EPS-SG) in the 2021-2040 time frame.…”

A simple and quick sensitivity analysis method for methane isotopologues detection with GOSAT-TANSO-FTS

“…Therefore, for this reason, and because measurements in the TiR are often more uncertain than SWiR measurements, exemplified in multiple studies [56][57][58], we decided to focus on the SWiR in this study. in addition, it has been shown that the SNR on the methane absorption regions in GOSAT are significantly lower than in the SWiR [56,59], suggesting that the This figure is as figure 5 in [27], but has been updated to reflect the use of hiTRAN2016.…”

Space-borne observation of methane from atmospheric infrared sounder: data analysis and distribution over Iraq

“…Grid maps coordinates range from -180.0° to +180.0° in longitude and from -90.0° to +90.0° in latitude [20]. Fifty to sixty bands of CH 4 absorption near (7.66 µm = 1306 cm -1 ) were selected for the CH 4 retrieval, and the atmospheric temperature profiles, water vapor profile, surface temperatures and surface emissivity are required as inputs to compute are derived from other AIRS channels [21].…”