Profiles of CH<sub>4</sub>, HDO, H<sub>2</sub>O, and N<sub>2</sub>O with improved lower tropospheric vertical resolution from Aura TES radiances

Abstract

Abstract. Thermal infrared (IR) radiances measured near 8 microns contain information about the vertical distribution of water vapor (H 2 O), the water isotopologue HDO, and methane (CH 4 ), key gases in the water and carbon cycles. Previous versions (Version 4 or less) of the TES profile retrieval algorithm used a "spectral-window" approach to minimize uncertainty from interfering species at the expense of reduced vertical resolution and sensitivity. In this manuscript we document changes to the vertical resolution and uncertainties of the TES version 5 retrieval algorithm. In this version (Version 5), joint estimates of H 2 O, HDO, CH 4 and nitrous oxide (N 2 O) are made using radiances from almost the entire spectral region between 1100 cm −1 and 1330 cm −1 . The TES retrieval constraints are also modified in order to better use this information. The new H 2 O estimates show improved vertical resolution in the lower troposphere and boundary layer, while the new HDO/H 2 O estimates can now profile the HDO/H 2 O ratio between 925 hPa and 450 hPa in the tropics and during summertime at high latitudes. The new retrievals are now sensitive to methane in the free troposphere between 800 and 150 mb with peak sensitivity near 500 hPa; whereas in previous versions the sensitivity peaked at 200 hPa. However, the upper troposphere methane concentrations are biased high relative to the lower troposphere by approximately 4 % on average. This bias is likely related to temperature, calibration, and/or methane spectroscopy errors. This bias can be mitigated by normalizing the CH 4 estimate by the ratio of the N 2 O estimate relative to the N 2 O prior, under the assumption that the same systematic error affects both the N 2 O and CH 4 estimates. We demonstrate that applying this ratio theoretically reduces the CH 4 estimate for non-retrieved parameters that jointly affect both the N 2 O and CH 4 estimates. The relative upper troposphere to lower troposphere bias is approximately 2.8 % after this bias correction. Quality flags based upon the vertical variability of the methane and N 2 O estimates can be used to reduce this bias further. While these new CH 4 , HDO/H 2 O, and H 2 O estimates are consistent with previous TES retrievals in the altitude regions where the sensitivities overlap, future comparisons with independent profile measurement will be required to characterize the biases of these new retrievals and determine if the calculated uncertainties using the new constraints are consistent with actual uncertainties.

Comparison of IASI water vapor retrieval with H<sub>2</sub>O-Raman lidar in the framework of the Mediterranean HyMeX and ChArMEx programs

“…A new generation of instruments has been launched on polar platforms satellites, such as Interferometric Monitor for Greenhouse gases (IMG, e.g., Ogawa et al, 1994;Clerbaux et al, 1998), Tropospheric Emission Spectrometer (TES, e.g., Shephard et al, 2008;Worden et al, 2012), the Advanced Infrared Sounder (AIRS, Chahine et al, 1990;Aumann and Miller, 1995), and the Infrared Atmospheric Sounding Interferometer (IASI, e.g., Clerbaux et al, 2009;Hilton et al, 2012). Thanks to a larger number of spectral channels and an enhanced spectral resolution, these instruments lead to improved vertical resolutions down to 1 km and higher precision of both the atmospheric temperature and water vapor content retrieval.…”

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

“…Because of a limited number of in situ measurements in time and space domain, the quantification of CH 4 emissions from different sources and in different regions still remains largely uncertain. In recent years, space-borne measurements of CH 4 from satellites have become available, such as the measurements using the thermal infrared (TIR) sensors, which include the Atmospheric InfraRed Sounder (AIRS) on NASA/Aqua (Aumann et al, 2003;Xiong et al, 2008Xiong et al, , 2010a, the Tropospheric Emission Spectrometer (TES) on NASA/Aura (Payne et al, 2009;Wecht et al, 2012;Worden et al, 2012), and the Infrared Atmospheric Sounding Interferometer (IASI) on METOP-A and METOP-B (Xiong et al, 2013;Crevoisiter et al, 2009Crevoisiter et al, , 2013Razavi et al, 2009). Measurements using the Near-Infrared (NIR) sensors include the SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY) instrument onboard ENVISAT for (Frankenberg et al, 2008, and the Thermal And Near infrared Sensor for carbon Observation (TANSO) onboard the Greenhouse gases Observation SATellite (GOSAT) from 2009 to present (Yokota et al, 2009;Paker et al, 2011;Schepers et al, 2012;Saitoh et al, 2012).…”

Observation of tropospheric δD by IASI over western Siberia: comparison with a general circulation model

“…This method also has the large advantage of minimizing the error on the δD profile (e.g. Schneider et al, 2006) as demonstrated for example by Worden et al (2006Worden et al ( , 2007Worden et al ( , 2012 on TES measurements, on IASI measurements by Schneider and Hase (2011) and Lacour et al (2012), or for ground-based measurements by Schneider et al (2006Schneider et al ( , 2010Schneider et al ( , 2012.…”

“…Prior to IASI, the Interferometric Monitor for Greenhouse gases (IMG) (Zakharov et al, 2004;Herbin et al, 2007) and the Tropospheric Emission Spectrometer (TES) provided quasi-global distributions of δD representative of the mid-troposphere (e.g. Worden et al, 2006Worden et al, , 2007 whereas the SCanning Imaging Absorption spectrometer for Atmospheric CartograpHY (SCIAMACHY) instrument provided total column distributions, with sensitivity down to the boundary layer (Frankenberg et al, 2009).…”