Characterization and validation of methane products from the Atmospheric Infrared Sounder (AIRS)

Abstract

[1] This paper presents the characterization and validation of retrievals of atmospheric methane (CH 4 ) vertical profiles by the Atmospheric Infrared Sounder (AIRS) on the EOS/Aqua platform. AIRS channels near 7.6 mm are used for CH 4 retrieval, and they are most sensitive to the middle to upper troposphere, i.e., about 200-300 hPa in the tropics and 400-500 hPa in the polar region. The atmospheric temperature-humidity profiles, surface skin temperature, and emissivity required to derive CH 4 are obtained from retrievals using separate AIRS channels and the Advanced Microwave Sounding Unit (AMSU). Comparison of AIRS retrieved profiles with some in situ aircraft CH 4 profiles implied that the forward model used in the AIRS retrieval system V4.0 required a 2% increase in methane absorption coefficients for strong absorption channels, and this bias adjustment was implemented in the AIRS retrieval system V5.0. As a new operational product in V5.0, AIRS CH 4 were validated using in situ aircraft observations at 22 sites of the NOAA Earth System Research Laboratory, Global Monitoring Division (NOAA/ESRL/GMD), ranging from the Arctic to the tropical South Pacific Ocean, but their altitudes are usually above 300 hPa. The results show the bias of the retrieved CH 4 profiles for this version is À1.4$0.1% and its RMS difference is about 0.5-1.6%, depending on altitude. These validation comparisons provide critical assessment of the retrieval algorithm and will continue using more in situ observations together with future improvement to the retrieval algorithm. AIRS CH 4 products include not only the CH 4 profile but also the information content. As examples, the products of AIRS CH 4 in August 2004 and the difference of CH 4 in May and September 2004 are shown. From these results a few features are evident: (1) a large AIRS CH 4 plume southwest of the Tibetan plateau that may be associated with deep convection during the Asian summer monsoon; (2) high mixing ratios of AIRS CH 4 in southeastern Asia and in the high northern hemisphere in the summer; and (3) the increase of AIRS CH 4 from May to September in the high northern hemisphere that is likely linked with wetland emission but needs more study. Further analysis of these data and its comparison with model data will be addressed in a separate paper.

Bias corrections of GOSAT SWIR XCO<sub>2</sub> and XCH<sub>4</sub> with TCCON data and their evaluation using aircraft measurement data

“…In order to test for remaining biases in the GOSAT data after applying the empirical correction developed using TCCON data, we use aircraft profile data provided by the Comprehensive Observation Network for TRace gases by AIrLiner (CONTRAIL) project (Machida et al, 2008), the NOAA Earth System Research Laboratory/Global Monitoring Division (ESRL/GMD; Xiong et al, 2008;Sweeney et al, 2015), the US Department of Energy (DOE; Biraud et al, 2013;Schmid et al, 2014), the National Institute for Environmental Studies (NIES; Machida et al, 2001), the Japan Meteorological Agency (JMA; Tsuboi et al, 2013), the HI-APER Pole-to-Pole Observations (HIPPO) project (Wofsy et al, 2011Kort et al, 2012;Santoni et al, 2014), and an aircraft measurement campaign by NIES and the Japan Aerospace Exploration Agency (JAXA) (Tanaka et al, 2012). To calculate aircraft-based XCO 2 and XCH 4 (as described in the next paragraph), we also used tower data from the Meteorological Research Institute (MRI) in Tsukuba (Inoue andMatsueda, 1996, 2001) and the NOAA ESRL/GMD tall tower network in Park Falls, WI and West Branch, IA .…”

Spatiotemporal variations in mid-upper tropospheric methane over China from satellite observations

“…Two major types of measurement are (1) the measurement of the total column using the nearinfrared spectrum and (2) the measurement of the mid-toupper troposphere methane (MUT-CH 4 ) using the thermal infrared spectrum with bands of 7.66, 3.3 and 2.3 m [13][14][15][16][17][18][19][20][21][22][23]. One of the spaceborne thermal infrared sounders in operation, the Atmospheric Infrared Sounder (AIRS), was launched in polar orbit (13:30, ascending node) on the EOS/Aqua satellite in May 2002; CH 4 is one of its research products [13,14].…”

Simulated retrievals for the remote sensing of CO<sub>2</sub>, CH<sub>4</sub>, CO, and H<sub>2</sub>O from geostationary orbit

“…2002 (Aumann et al, 2003;Chahine et al, 2005Chahine et al, , 2008Xiong et al, 2008). The Scanning Imaging Absorption Spectrometer for Atmospheric Cartography (SCIAMACHY) instrument was operational for measurements of atmospheric compositions from 2002 to 2012, with CO 2 , CH 4 , CO, and H 2 O as four of its target species (Buchwitz et al, 2004(Buchwitz et al, , 2007Schrijver et al, 2009;Schneising et al, 2011).…”