17 results found
Murray JE, Brindley HE, Fox S, et al., 2020, Retrievals of high latitude surface emissivity across the infrared from high altitude aircraft flights, Journal of Geophysical Research: Atmospheres, Vol: 125, Pages: 1-16, ISSN: 2169-897X
We present retrievals of infrared spectral surface emissivities spanning the far and mid infrared from aircraft observations over Greenland, taken at an altitude of 9.2 km above sea level. We describe the flight campaign, available measurements and the retrieval method. The principal barriers to reducing uncertainty in the emissivity retrievals are found to be instrumental noise and our ability to simultaneously retrieve the underlying surface temperature. However, our results indicate that using the instrumentation available to us it is possible to retrieve emissivities from altitude with an uncertainty of ~ 0.02 or better across much of the infrared. They confirm that the far‐infrared emissivity of snow and ice surfaces can depart substantially from unity, reaching values as low as 0.9 between 400‐450 cm‐1. They also show good consistency with retrievals from the same flight made from near‐surface observations giving confidence in the methodology used and the results obtained for this more challenging viewing configuration. To the best of our knowledge, this is the first time that far‐infrared surface emissivity has been retrieved from altitude and demonstrates that the methodology has the potential to be extended to planned satellite far‐infrared missions.
Bantges RJ, Brindley HE, Murray JE, et al., 2020, A test of the ability of current bulk optical models to represent the radiative properties of cirrus cloud across the mid- and far-infrared, Atmospheric Chemistry and Physics, Vol: 20, Pages: 12889-12903, ISSN: 1680-7316
Measurements of mid- to far-infrared nadir radiances obtained from the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 aircraft during the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX) are used to assess the performance of various ice cloud bulk optical property models. Through use of a minimization approach, we find that the simulations can reproduce the observed spectra in the mid-infrared to within measurement uncertainty, but they are unable to simultaneously match the observations over the far-infrared frequency range. When both mid- and far-infrared observations are used to minimize residuals, first-order estimates of the spectral flux differences between the best-performing simulations and observations indicate a compensation effect between the mid- and far-infrared such that the absolute broadband difference is < 0.7 W m−2. However, simply matching the spectra using the mid-infrared (far-infrared) observations in isolation leads to substantially larger discrepancies, with absolute differences reaching ∼ 1.8 (3.1) W m−2. These results show that simulations using these microphysical models may give a broadly correct integrated longwave radiative impact but that this masks spectral errors, with implicit consequences for the vertical distribution of atmospheric heating. They also imply that retrievals using these models applied to mid-infrared radiances in isolation will select cirrus optical properties that are inconsistent with far-infrared radiances. As such, the results highlight the potential benefit of more extensive far-infrared observations for the assessment and, where necessary, the improvement of current ice bulk optical models.
Bantges R, Brindley H, Russell J, et al., 2020, A test of the ability of current bulk optical models to represent the radiative properties of cirrus cloud across the mid-and far-infrared, Publisher: Atmospheric Chemistry and Physics. Discussion. Copernicus Publications
Measurements of mid- to far-infrared nadir radiances obtained from the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 aircraft during the Cirrus Coupled Cloud-Radiation Experiment (CIRCCREX) are used to assess the performance of various ice cloud bulk optical (single-scattering) property models. Through use of a minimisation approach, we find that the simulations can reproduce the observed spectra in the mid-infrared to within measurement uncertainty but are unable to simultaneously match the observations over the far-infrared frequency range. When both mid and far-infrared observations are used to minimise residuals, first order estimates of the flux differences between the best performing simulations and observations indicate a strong compensation effect between the mid and far infrared such that the absolute broadband difference is < 0.7 W m−2. However, simply matching the spectra using the mid-infrared observations in isolation leads to substantially larger discrepancies, with absolute differences reaching ~ 1.8 W m−2. These results highlight the benefit of far infrared observations for better constraining retrievals of cirrus cloud properties and their radiative impact, and provide guidance for the development of more realistic ice cloud optical models.
Parfitt R, Russell JE, Bantges RJ, et al., 2016, A study of the time evolution of GERB shortwave calibration by comparison with CERES Edition-3A data, Remote Sensing of Environment, Vol: 186, Pages: 416-427, ISSN: 0034-4257
This study examines the evolution of the GERB-2 and GERB-1 Edition 1 shortwave radiance calibration between 2004-2007 and 2007-2012 respectively, through comparison with CERES instrument FM1 Edition 3A SSF instantaneous radiances. Two periods when simultaneous observations from both GERB-2 and GERB-1 were available, January 13th to February 11th 2007 and May 1st to May 10th 2007, are also compared. For these two overlap periods respectively, averaged over all CERES ‘unfiltered-to-filtered radiance ratio’ subsets, the GERB-1/CERES unfiltered radiance ratio is on average found to be 1.6% and 1.9% lower than the associated GERB-2/CERES unfiltered radiance ratio. Over the two longer time series the GERB/CERES unfiltered radiance ratio shows a general decrease with time for both GERB-2 and GERB-1. The rate of decrease varies through time but no significant seasonal dependence is seen. Averaged over all subsets the GERB-2/CERES unfiltered radiance ratio showed a decrease of 1.9% between June 2004 and June 2006. Between June 2007 and June 2012, the corresponding decrease in the GERB-1/CERES unfiltered radiance ratio was 6.5%. The evolution of the GERB/CERES unfiltered radiance ratio for both GERB-2 and GERB-1 shows a strong dependence on the CERES unfiltered-to-filtered radiance ratio, indicating that it is spectrally dependent. Further time-series analysis and theoretical work using simulated spectral radiance curves suggests that for GERB-1 the evolution is consistent with a darkening in the GERB shortwave spectral response function which is most pronounced at the shortest wavelengths. For GERB-2, no single spectral cause can be identified, suggesting that the evolution is likely due to a combination of several different effects.
Brindley HE, Bantges RJ, 2016, The spectral signature of recent climate change, Current Climate Change Reports, Vol: 2, Pages: 112-126, ISSN: 2198-6061
Spectrally resolved measurements of the Earth’s reflected shortwave (RSW) and outgoing longwave radiation (OLR) at the top of the atmosphere intrinsically contain the imprints of a multitude of climate relevant parameters. Here, we review the progress made in directly using such observations to diagnose and attribute change within the Earth system over the past four decades. We show how changes associated with perturbations such as increasing greenhouse gases are expected to be manifested across the spectrum and illustrate the enhanced discriminatory power that spectral resolution provides over broadband radiation measurements. Advances in formal detection and attribution techniques and in the design of climate model evaluation exercises employing spectrally resolved data are highlighted. We illustrate how spectral observations have been used to provide insight into key climate feedback processes and quantify multi-year variability but also indicate potential barriers to further progress. Suggestions for future research priorities in this area are provided.
Bantges RJ, Brindley HE, Chen XH, et al., 2016, On the detection of robust multi-decadal changes in the Earth’s Outgoing Longwave Radiation spectrum, Journal of Climate, Vol: 29, Pages: 4939-4947, ISSN: 1520-0442
Differences between Earth’s global mean all-sky outgoing longwave radiation spectrum as observed in 1970 [Interferometric Infrared Spectrometer (IRIS)], 1997 [Interferometric Monitor for Greenhouse Gases (IMG)], and 2012 [Infrared Atmospheric Sounding Instrument (IASI)] are presented. These differences are evaluated to determine whether these are robust signals of multidecadal radiative forcing and hence whether there is the potential for evaluating feedback-type responses. IASI–IRIS differences range from +2 K in the atmospheric window (800–1000 cm−1) to −5.5 K in the 1304 cm−1 CH4 band center. Corresponding IASI–IMG differences are much smaller, at 0.2 and −0.8 K, respectively. More noticeably, IASI–IRIS differences show a distinct step change across the 1042 cm−1 O3 band that is not seen in IASI–IMG comparisons. This step change is a consequence of a difference in behavior when moving from colder to warmer scenes in the IRIS data compared to IASI and IMG. Matched simulations for the relevant periods using ERA reanalyses mimic the spectral behavior shown by IASI and IMG rather than by IRIS. These findings suggest that uncertainties in the spectral response of IRIS preclude the use of these data for quantitative assessments of forcing and feedback processes.
Brindley H, Osipov S, Bantges R, et al., 2015, An assessment of the quality of aerosol retrievals over the Red Sea and evaluation of the climatological cloud-free dust direct radiative effect in the region, Journal of Geophysical Research: Atmospheres, Vol: 120, ISSN: 2169-897X
Ground-based and satellite observations are used in conjunction with the Rapid RadiativeTransfer Model (RRTM) to assess climatological aerosol loading and the associated cloud-free aerosol directradiative effect (DRE) over the Red Sea. Aerosol optical depth (AOD) retrievals from the Moderate ResolutionImaging Spectroradiometer and Spinning Enhanced Visible and InfraRed Imager (SEVIRI) instruments are firstevaluated via comparison with ship-based observations. Correlations are typically better than 0.9 with verysmall root-mean-square and bias differences. Calculations of the DRE along the ship cruises using RRTM alsoshow good agreement with colocated estimates from the Geostationary Earth Radiation Budget instrumentif the aerosol asymmetry parameter is adjusted to account for the presence of large particles. A monthlyclimatology of AOD over the Red Sea is then created from 5 years of SEVIRI retrievals. This shows enhancedaerosol loading and a distinct north to south gradient across the basin in the summer relative to the wintermonths. The climatology is used with RRTM to estimate the DRE at the top and bottom of the atmosphereand the atmospheric absorption due to dust aerosol. These climatological estimates indicate that althoughlongwave effects can reach tens of W m 2, shortwave cooling typically dominates the net radiativeeffect over the Sea, being particularly pronounced in the summer, reaching 120 W m 2 at the surface.The spatial gradient in summertime AOD is reflected in the radiative effect at the surface and in associateddifferential heating by aerosol within the atmosphere above the Sea. This asymmetric effect is expected toexert a significant influence on the regional atmospheric and oceanic circulation.
Wielicki BA, Young DF, Mlynczak MG, et al., 2013, Achieving Climate Change Absolute Accuracy in Orbit, BULLETIN OF THE AMERICAN METEOROLOGICAL SOCIETY, Vol: 94, Pages: 1519-1539, ISSN: 0003-0007
Clerbaux N, Russell JE, Dewitte S, et al., 2009, Comparison of GERB instantaneous radiance and flux products with CERES Edition-2 data, REMOTE SENSING OF ENVIRONMENT, Vol: 113, Pages: 102-114, ISSN: 0034-4257
Bantges RJ, Russell JE, Harries JE, et al., 2009, A Geostationary Earth Radiation Budget Dataset For Climate Research: First Intercomparison Results Between Data From the GERB-1 &-2 Instruments, International Radiation Symposium (IRC/IAMAS), Publisher: AMER INST PHYSICS, Pages: 513-516, ISSN: 0094-243X
Blyth E, Evans J, Finch J, et al., 2006, Spatial variability of the English agricultural landscape and its effect on evaporation, Agricultural and Forest Meteorology, Vol: 138, Pages: 19-28
The variability of leaf area index, canopy height and albedo is measured across an agricultural landscape in lowland Britain. The dependency of the variability with spatial sampling is quantified and the sensitivity of modelled evaporation to the variability is assessed. From this study, it appears that the leaf area index can display significant variability between fields of growing crops as their plant and harvest times may differ by the order of a month. In addition the albedo variability is high. Both these quantities have an influence on the resulting evaporation (between 1% and 40% depending on assumptions) and need to be accounted for. Although the crop height varies considerably, it does not have a big impact on evaporation (less than 4%).
Harries JE, Brindley HE, Sagoo PJ, et al., 2001, Increase in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997 (vol 410, pg 355, 2001), NATURE, Vol: 410, Pages: 1124-1124, ISSN: 0028-0836
Harries JE, Brindley HE, Sagoo PJ, et al., 2001, Increases in greenhouse forcing inferred from the outgoing longwave radiation spectra of the Earth in 1970 and 1997, NATURE, Vol: 410, Pages: 355-357, ISSN: 0028-0836
Bantges RJ, Russell JE, Haigh JD, 1999, Cirrus cloud top-of-atmosphere radiance spectra in the thermal infrared, Conference on Light Scattering by Nonspherical Particles - Theory, Measurements, and Applications, Publisher: PERGAMON-ELSEVIER SCIENCE LTD, Pages: 487-498, ISSN: 0022-4073
Bantges RJ, Russell JE, Haigh JD, 1999, Cirrus cloud top-of-atmosphere radiance spectra in the thermal infrared, Journal of Quantitative Spectroscopy & Radiative Transfer, Vol: 63, Pages: 487-498
Russell JE, Bantges RJ, Haigh JD, et al., 1998, Retrieval of cirrus properties from high spectral resolution IR measurements, Conference on Satellite Remote Sensing of Clouds and the Atmosphere II, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, Pages: 60-71, ISSN: 0277-786X
Russell JE, Bantges RJ, Naud C, et al., 1998, The effect of cirrus cloud in the infrared (4-100 microns) - high spectral resolution simulations, Conference on Satellite Remote Sensing of Clouds and the Atmosphere III, Publisher: SPIE-INT SOC OPTICAL ENGINEERING, Pages: 100-108, ISSN: 0277-786X
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