Water vapour line and continuum absorption in the thermal infrared—reconciling models and observations

Taylor, Jonathan; Newman, Stuart M.; Hewison, Tim J.; McGrath, Andrew

doi:10.1256/003590003769682129

Cited by 5 publications

(7 citation statements)

References 6 publications

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“…The data set includes 33 profiles covering a range of conditions from tropical to arctic. A subset of this data set has been used to validate infrared absorption models using measurements from an interferometer on the same aircraft [ Taylor et al , 2003]. Low‐level zenith infrared observations in the tropics suggest the self‐broadening coefficient of the CKD2.4 water vapor continuum is too strong by 6–15%, dependent on frequency.…”

Section: Discussionmentioning

confidence: 99%

“…During 1999, the UK Met Office conducted two field experiments, with the objective of the Measurement of Tropospheric Humidity (MOTH) [ Taylor et al , 2003]. The first of these was based on Ascension Island in the South Atlantic during April‐May, where Integrated Water Vapor (IWV) column amounts from 29–42 kg/m 2 were measured by aircraft instruments during profiles.…”

Section: Measurementsmentioning

confidence: 99%

“…During 1999, the UK Met Office conducted a campaign named MOTH (Measurement Of Tropospheric Humidity) to improve our understanding of water vapor observations. Data from an airborne interferometer during MOTH have been used to validate models in the infrared [ Taylor et al , 2003]. This paper reports how data from this campaign and others have been used to validate microwave absorption models at 89–183 GHz, where absorption is dominated by water vapor.…”

Section: Introductionmentioning

confidence: 99%

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Aircraft validation of clear air absorption models at millimeter wavelengths (89–183 GHz)

Hewison¹

2006

J. Geophys. Res.

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[1] Measurements with an airborne microwave radiometer are used to validate absorption models in clear air at frequencies used in satellite microwave humidity sounders, such as AMSU-B and MHS. The data set includes 33 profiles of radiometric and in situ observations ranging from the tropics to the high arctic. In cold, dry conditions the MPM and Rosenkranz models were found to underestimate the observed downwelling radiances near the surface in window channels dominated by the water vapor continuum. The models' absorption coefficient is calculated and found to be strongly deficient compared to observations in layers of low specific humidity. For medium humidity, the models' negative bias persists at 89 GHz and becomes statistically significant, but reduces at higher frequencies. Previously, the radiometer calibration had been adjusted to fit modeled radiances during high-level flight; this approach has been revised in the light of these findings and a tip curve method applied. Possible spectroscopic reasons for the models' deficits are suggested, including the underestimation of continuum terms or the extrapolation of oxygen line coupling coefficients to low temperatures. The impacts for operational use of radiative transfer models are discussed.

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Section: Discussionmentioning

confidence: 99%

Section: Measurementsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Aircraft validation of clear air absorption models at millimeter wavelengths (89–183 GHz)

Hewison¹

2006

J. Geophys. Res.

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“…Some important instruments on the C-130 included the microwave radiometers MARSS and Deimos, which are described below; a Heimann KT 19.82 infrared radiometer with a fixed downward field of view; navigational equipment that provided information about the position and attitude of the aircraft; a General Eastern chilled-mirror hygrometer; and other in situ instruments that provided, among others, measurements of air temperature, pressure, and humidity content. More information about the aircraft instrumentation may be found in Selbach (2003) and Taylor et al (2003).…”

Section: A Aircraft Campaignmentioning

confidence: 99%

Airborne Retrievals of Snow Microwave Emissivity at AMSU Frequencies Using ARTS/SCEM-UA

Harlow

2007

Journal of Applied Meteorology and Climatology

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The remote sounding, by satellite, of atmospheric temperature and humidity is an important source of data for assimilation into operational weather forecasting routines. For retrievals of these variables near the surface, wavebands with low optical depths are monitored to allow penetration through the overlying atmosphere. Brightness temperatures in these relatively transparent bands are also sensitive to the land surface emissivity and effective temperature. Inadequate understanding of these land surface emissivities is a major issue when assimilating Advanced Microwave Sounding Unit data for the land-covered portion of the globe. One approach for estimating the emissivity of snow-covered surfaces is an empirical model derived from satellite-based and land-based retrievals of emissivity for a variety of snow types. The Met Office's Hercules C-130 aircraft flew over snow-covered Arctic terrain of northern Finland during the Polar Experiment (POLEX) of March 2001. On these flights, microwave radiometers provided microwave brightness temperatures at 23.8, 50.3, 89.0, 157, and 183 GHz. The work presented here uses these data along with a robust multiparameter optimization routine [Shuffled Complex Evolution Metropolis (SCEM-UA)] coupled to the Atmospheric Radiative Transfer Simulator (ARTS) to retrieve emissivities at the measured frequencies. These results are then used to validate an empirical model. This latter model predicts 23.8-157-GHz emissivities with an RMSE of less than 0.02 and bias of less than 0.01 when compared with data at an incidence angle of 40°. Nonmonotonic behavior in the emissivity spectrum for this campaign, reported in earlier work, is confirmed by the retrievals presented here.

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“…The high spectral resolution and excellent radiometric calibration and noise characteristics of the instrument have also allowed ARIES to be used to validate and characterise improvements in reference spectroscopic datasets such as the HIgh-resolution TRANsmission molecular absorption (HITRAN) database (e.g. Newman and Taylor, 2002;Tjemkes et al, 2003); and to make direct measurements of the H 2 O continuum (Taylor et al, 2003).…”

Section: The Ariesmentioning

confidence: 99%

Atmospheric composition and thermodynamic retrievals from the ARIES airborne FTS system – Part 1: Technical aspects and simulated capability

Illingworth¹,

Allen²,

Newman³

et al. 2013

Preprint

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Abstract. In this study we present an assessment of the retrieval capability of the Airborne Research Interferometer Evaluation System (ARIES); an airborne remote sensing Fourier Transform Spectrometer (FTS) operated on the UK Facility for Airborne Atmospheric Measurement (FAAM) aircraft. Simulated optimally-estimated-retrievals of partial column trace gas concentrations, and thermodynamic vertical profiles throughout the troposphere and planetary boundary layer have been performed here for simulated infrared spectra representative of the ARIES system. We also describe the operational and technical aspects of the pre-processing necessary for routine retrieval from the FAAM platform and the selection and construction of a priori information. As exemplars of the capability of the ARIES retrieval system, simulated retrievals of temperature, water vapour (H2O), carbon monoxide (CO), ozone (O3), and methane (CH4), and their corresponding sources of error and potential vertical sensitivity, are discussed for ARIES scenes across typical global environments. The maximum Degrees of Freedom for Signal (DOFS) for the retrievals, assuming a flight altitude of 7 km, were: 3.99, 2.97, 0.85, 0.96, and 1.45 for temperature, H2O, CO, O3, and CH4, respectively for the a priori constraints specified. Retrievals of temperature display significant vertical sensitivity (DOFS in the range 2.6 to 4.0 across the altitude range) as well as excellent simulated accuracy, with the vertical sensitivity for H2O also extending to lower altitudes (DOFS ranging from 1.6 to 3.0). It was found that the maximum sensitivity for CO, O3, and CH4 was approximately 1–2 km below the simulated altitudes in all scenarios. Comparisons of retrieved and simulated-truth partial atmospheric columns are used to assess the capability of the ARIES measurement system. Maximum mean biases (and bias standard deviations) in partial columns (i.e. below aircraft total columns) were found to be: +0.06 (±0.02 at 1σ) %, +3.95 (±3.11)%, +3.74 (±2.97)%, −8.26 (±4.64)% and +3.01 (±2.61)% for temperature, H2O, CO, O3, and CH4 respectively, illustrating that the retrieval system performs well compared to an optimal scheme. The maximum total a posteriori retrieval errors across the partial columns were also calculated, and were found to be 0.20%, 22.57%, 18.22%, 17.61%, and 16.42% for temperature, H2O, CO, O3, and CH4 respectively.

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Water vapour line and continuum absorption in the thermal infrared—reconciling models and observations

Cited by 5 publications

References 6 publications

Aircraft validation of clear air absorption models at millimeter wavelengths (89–183 GHz)

Aircraft validation of clear air absorption models at millimeter wavelengths (89–183 GHz)

Airborne Retrievals of Snow Microwave Emissivity at AMSU Frequencies Using ARTS/SCEM-UA

Atmospheric composition and thermodynamic retrievals from the ARIES airborne FTS system – Part 1: Technical aspects and simulated capability

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