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Water Vapour and Methane Coupling in the Stratosphere observed with SCIAMACHY Solar Occultation Measurements
摘要： An improved stratospheric water vapour dataset has been derived from SCIAMACHY/ENVISAT solar occultation measurements. It is based on the same algorithm which has already been successfully applied to methane and carbon dioxide retrievals, thus resulting in a consistent dataset for these three constituents covering the altitudes 17–45 km, the latitude range between about 50 and 70?N, and the time interval August 2002 to April 2012. The new water vapour data agree with collocated results from ACE-FTS and MLS/Aura within about 5%. A significant positive water vapour trend for the time 2003–2011 is observed at lower stratospheric altitudes of about 0.015 ppmv year?1 around 17 km. Between 30 and 37 km the trend becomes significantly negative (about -0.01 ppmv year?1). The combined analysis of the SCIAMACHY methane and water vapour time series reveals that stratospheric methane and water vapour are strongly correlated and show a clear temporal variation related to the Quasi-Biannual-Oscillation (QBO). Above about 20 km most of the water vapour seems to be produced by methane, but short-term fluctuations and a temporal variation on a scale of 5–6 years are observed. At lower altitudes the balance between water vapour and methane is affected by stratospheric transport of water vapour and methane from the tropics to higher latitudes via the shallow branch of the Brewer-Dobson circulation and by the increasing methane input into the stratosphere due to the rise of tropospheric methane after 2007.
关键词： stratospheric water vapour,Quasi-Biannual-Oscillation,solar occultation,Brewer-Dobson circulation,methane,SCIAMACHY,carbon dioxide
更新于2025-09-09 09:28:46
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Automated characterization and quantification of hydrocarbon seeps based on frontal illuminated video observations
摘要： Hydrocarbon releases, either natural or due to anthropogenic activities, are of major relevance for the marine environment. In this work we specify our approach to quantify these seeps by subsea imaging utilizing camera systems and frontal illumination setups on board remotely operated vehicles. This work showcases, based on a campaign in the region west of Svalbard, improved methodological guidelines for the seep quantification operation together with a novel automated post-mission evaluation. The comparison of automated quantification with manual information extraction illustrates the efficiency of this new method while processing comparable estimates of seep characteristics.
关键词： gas flux,bubbles,Methane,imaging,Svalbard
更新于2025-09-09 09:28:46
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Quantifying lower tropospheric methane concentrations using GOSAT near-IR and TES thermal IR measurements
摘要： Evaluating surface fluxes of CH4 using total column data requires models to accurately account for the transport and chemistry of methane in the free troposphere and stratosphere, thus reducing sensitivity to the underlying fluxes. Vertical profiles of methane have increased sensitivity to surface fluxes because lower tropospheric methane is more sensitive to surface fluxes than a total column, and quantifying free-tropospheric CH4 concentrations helps to evaluate the impact of transport and chemistry uncertainties on estimated surface fluxes. Here we demonstrate the potential for estimating lower tropospheric CH4 concentrations through the combination of free-tropospheric methane measurements from the Aura Tropospheric Emission Spectrometer (TES) and XCH4 (dry-mole air fraction of methane) from the Greenhouse gases Observing SATellite – Thermal And Near-infrared for carbon Observation (GOSAT TANSO, herein GOSAT for brevity). The calculated precision of these estimates ranges from 10 to 30 ppb for a monthly average on a 4? × 5? latitude/longitude grid making these data suitable for evaluating lower-tropospheric methane concentrations. Smoothing error is approximately 10 ppb or less. Comparisons between these data and the GEOS-Chem model demonstrate that these lower-tropospheric CH4 estimates can resolve enhanced concentrations over flux regions that are challenging to resolve with total column measurements. We also use the GEOS-Chem model and surface measurements in background regions across a range of latitudes to determine that these lower-tropospheric estimates are biased low by approximately 65 ppb, with an accuracy of approximately 6 ppb (after removal of the bias) and an actual precision of approximately 30 ppb. This 6 ppb accuracy is consistent with the accuracy of TES and GOSAT methane retrievals.
关键词： methane,remote sensing,GOSAT,TES,lower troposphere
更新于2025-09-04 15:30:14
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Characterization of anthropogenic methane plumes with the Hyperspectral Thermal Emission Spectrometer (HyTES): a retrieval method and error analysis
摘要： We introduce a retrieval algorithm to estimate lower tropospheric methane (CH4) concentrations from the surface to 1 km with uncertainty estimates using Hyperspectral Thermal Emission Spectrometer (HyTES) airborne radiance measurements. After resampling, retrievals have a spatial resolution of 6 × 6 m2. The total error from a single retrieval is approximately 20 %, with the uncertainties determined primarily by noise and spectral interferences from air temperature, surface emissivity, and atmospheric water vapor. We demonstrate retrievals for a HyTES flight line over storage tanks near Kern River Oil Field (KROF), Kern County, California, and find an extended plume structure in the set of observations with elevated methane concentrations (3.0 ± 0.6 to 6.0 ± 1.2 ppm), well above mean concentrations (1.8±0.4 ppm) observed for this scene. With typically a 20 % estimated uncertainty, plume enhancements with more than 1 ppm are distinguishable from the background values with its uncertainty. HyTES retrievals are consistent with simultaneous airborne and ground-based in situ CH4 mole fraction measurements within the reported accuracy of approximately 0.2 ppm (or ～ 8 %), due to retrieval interferences related to air temperature, emissivity, and H2O.
关键词： methane,airborne measurements,error analysis,retrieval algorithm,HyTES
更新于2025-09-04 15:30:14
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Methane on Mars: New insights into the sensitivity of CH4 with the NOMAD/ExoMars spectrometer through its first in-flight calibration
摘要： The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibration was achieved, together with its variability due to thermal effects on the grating. The AOTF properties and transfer function were also quantified, and we developed and tested a realistic method to compute the spectral continuum transmitted through the coupled grating and AOTF system. The calibration results enabled unprecedented insights into the important problem of the sensitivity of NOMAD to methane abundances in the atmosphere. We also deeply characterized its performance under realistic conditions of varying aerosol abundances, diverse albedos and changing illumination conditions as foreseen over the nominal mission. The results show that, in low aerosol conditions, NOMAD single spectrum, 1σ sensitivity to CH4 is around 0.33 ppbv at 20 km of altitude when performing solar occultations, and better than 1 ppbv below 30 km. In dusty conditions, we show that the sensitivity drops to 0 below 10 km. In Nadir geometry, results demonstrate that NOMAD will be able to produce seasonal maps of CH4 with a sensitivity around 5 ppbv over most of planet's surface with spatial integration over 5 × 5° bins. Results show also that such numbers can be improved by a factor of ~10 to ~30 by data binning. Overall, our results quantify NOMAD's capability to address the variable aspects of Martian climate.
关键词： NOMAD,Instrumentation,Infrared spectroscopy,Mars atmosphere,Methane
更新于2025-09-04 15:30:14
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EXPRESS: Mid-Infrared Polarization Spectroscopy Measurements of Species Concentrations and Temperature in a Low-Pressure Flame
摘要： We demonstrate quantitative measurements of methane (CH4) mole fractions in a low pressure fuel-rich premixed dimethyl ether/oxygen/argon flat flame (Φ =1.87, 37 mbar) using mid-infrared polarization spectroscopy (IRPS). Nonintrusive in situ detection of CH4, acetylene (C2H2), and ethane (C2H6) in the flame was realized by probing the fundamental asymmetric C–H stretching vibration bands in the respective molecules in the spectral range 2970–3340 cm–1. The flame was stabilized on a McKenna-type porous plug burner hosted in a low pressure chamber. The temperature at different heights above the burner (HAB) was measured from the line ratio of temperature sensitive H2O spectral lines recorded using IRPS. Quantitative measurements of CH4 mole fractions at different HAB in the flame were realized by a calibration measurement in a low pressure gas flow of N2 with a small admixture of known amount of CH4. A comprehensive study of the collision effects on the IRPS signal was performed in order to quantify the flame measurement. The concentration and temperature measurements were found to agree reasonably well with simulations using Chemkin. These measurements prove the potential of IRPS as a sensitive, nonintrusive, in situ technique in low pressure flames.
关键词： dimethyl ether,methane,Mid-infrared polarization spectroscopy,quantitative concentrations,low pressure flame,temperature
更新于2025-09-04 15:30:14