scholarly journals Can downwelling far-infrared radiances over Antarctica be estimated from mid-infrared information?

2019 ◽  
Vol 19 (11) ◽  
pp. 7927-7937
Author(s):  
Christophe Bellisario ◽  
Helen E. Brindley ◽  
Simon F. B. Tett ◽  
Rolando Rizzi ◽  
Gianluca Di Natale ◽  
...  
Keyword(s):  
Climate Models ◽  
Far Infrared ◽  
Mid Infrared ◽  
Spectral Bands ◽  
Noise Characteristics ◽  
Infrared Spectral ◽  
Infrared Radiances ◽  
Spectrally Resolved ◽  
Spectral Ranges ◽  
The Impact

Abstract. Far-infrared (FIR: 100cm-1<wavenumber, ν<667 cm−1) radiation emitted by the Earth and its atmosphere plays a key role in the Earth's energy budget. However, because of a lack of spectrally resolved measurements, radiation schemes in climate models suffer from a lack of constraint across this spectral range. Exploiting a method developed to estimate upwelling far-infrared radiation from mid-infrared (MIR: 667cm-1<ν<1400 cm−1) observations, we explore the possibility of inferring zenith FIR downwelling radiances in zenith-looking observation geometry, focusing on clear-sky conditions in Antarctica. The methodology selects a MIR predictor wavenumber for each FIR wavenumber based on the maximum correlation seen between the different spectral ranges. Observations from the REFIR-PAD instrument (Radiation Explorer in the Far Infrared – Prototype for Application and Development) and high-resolution radiance simulations generated from co-located radio soundings are used to develop and assess the method. We highlight the impact of noise on the correlation between MIR and FIR radiances by comparing the observational and theoretical cases. Using the observed values in isolation, between 150 and 360 cm−1, differences between the “true” and “extended” radiances are less than 5 %. However, in spectral bands of low signal, between 360 and 667 cm−1, the impact of instrument noise is strong and increases the differences seen. When the extension of the observed spectra is performed using regression coefficients based on noise-free radiative transfer simulations the results show strong biases, exceeding 100 % where the signal is low. These biases are reduced to just a few percent if the noise in the observations is accounted for in the simulation procedure. Our results imply that while it is feasible to use this type of approach to extend mid-infrared spectral measurements to the far-infrared, the quality of the extension will be strongly dependent on the noise characteristics of the observations. A good knowledge of the atmospheric state associated with the measurements is also required in order to build a representative regression model.

scholarly journals FORUM: Unique Far-Infrared Satellite Observations to Better Understand How Earth Radiates Energy to Space

2020 ◽  
Vol 101 (12) ◽  
pp. E2030-E2046 ◽  
Author(s):  
L. Palchetti ◽  
H. Brindley ◽  
R. Bantges ◽  
S. A. Buehler ◽  
C. Camy-Peyret ◽  
...  
Keyword(s):  
Climate Models ◽  
Longwave Radiation ◽  
Far Infrared ◽  
Lapse Rate ◽  
High Spectral Resolution ◽  
Critical Parameters ◽  
Temperature Lapse Rate ◽  
Stratospheric Water Vapor ◽  
Explorer Mission ◽  
Spectrally Resolved

AbstractThe outgoing longwave radiation (OLR) emitted to space is a fundamental component of the Earth’s energy budget. There are numerous, entangled physical processes that contribute to OLR and that are responsible for driving, and responding to, climate change. Spectrally resolved observations can disentangle these processes, but technical limitations have precluded accurate space-based spectral measurements covering the far infrared (FIR) from 100 to 667 cm−1 (wavelengths between 15 and 100 µm). The Earth’s FIR spectrum is thus essentially unmeasured even though at least half of the OLR arises from this spectral range. The region is strongly influenced by upper-tropospheric–lower-stratospheric water vapor, temperature lapse rate, ice cloud distribution, and microphysics, all critical parameters in the climate system that are highly variable and still poorly observed and understood. To cover this uncharted territory in Earth observations, the Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission has recently been selected as ESA’s ninth Earth Explorer mission for launch in 2026. The primary goal of FORUM is to measure, with high absolute accuracy, the FIR component of the spectrally resolved OLR for the first time with high spectral resolution and radiometric accuracy. The mission will provide a benchmark dataset of global observations which will significantly enhance our understanding of key forcing and feedback processes of the Earth’s atmosphere to enable more stringent evaluation of climate models. This paper describes the motivation for the mission, highlighting the scientific advances that are expected from the new measurements.

scholarly journals Can downwelling far-infrared radiances over Antarctica be estimated from mid-infrared information?

2018 ◽  
Author(s):  
Christophe Bellisario ◽  
Helen E. Brindley ◽  
Simon F. B. Tett ◽  
Rolando Rizzi ◽  
Gianluca Di Natale ◽  
...  
Keyword(s):  
Far Infrared ◽  
Mid Infrared ◽  
Infrared Radiances

Abstract. Far-infrared (FIR: 100 cm−1 

scholarly journals Microspectroscopic infrared specular reflection chemical imaging of multi-component urinary stones: MIR vs. FIR

2014 ◽  
Vol 12 (1) ◽  
pp. 44-52 ◽  
Author(s):  
Milda Pucetaite ◽  
Sandra Tamosaityte ◽  
Anders Engdahl ◽  
Justinas Ceponkus ◽  
Valdas Sablinskas ◽  
...  
Keyword(s):  
Diffuse Reflection ◽  
Specular Reflection ◽  
Far Infrared ◽  
Chemical Imaging ◽  
Urinary Stones ◽  
High Contrast ◽  
Mid Infrared ◽  
Infrared Microspectroscopy ◽  
Spectral Bands ◽  
Far Infrared Radiation

AbstractSpecular reflection infrared microspectroscopy was used for chemical imaging of cross-sectioned urinary stones to determine their chemical composition and morphology simultaneously. Absorption spectral bands were recovered from reflection spectra by Kramers-Kronig transform. FUse of far-infrared radiation provides high-contrast images and allows more precise constituent distribution determinations than mid-infrared because band asymmetry after the transform caused by diffuse reflection is less in the far-infrared.

scholarly journals A test of the ability of current bulk optical models to represent the radiative properties of cirrus cloud across the mid- and far-infrared

2020 ◽  
Vol 20 (21) ◽  
pp. 12889-12903 ◽  
Author(s):  
Richard J. Bantges ◽  
Helen E. Brindley ◽  
Jonathan E. Murray ◽  
Alan E. Last ◽  
Jacqueline E. Russell ◽  
...  
Keyword(s):  
Far Infrared ◽  
Radiative Properties ◽  
Atmospheric Measurements ◽  
Mid Infrared ◽  
Infrared Observations ◽  
Ice Cloud ◽  
Spectral Flux ◽  
Infrared Frequency Range ◽  
Infrared Radiances ◽  
The Uk

Abstract. 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.

Spectrally resolved OLR from IASI measurements

2020 ◽  
Author(s):  
Simon Whitburn ◽  
Lieven Clarisse ◽  
Sophie Bauduin ◽  
Steven Dewitte ◽  
Maya George ◽  
...  
Keyword(s):  
Spectral Range ◽  
Climate Models ◽  
Southern Oscillation ◽  
Radiation Budget ◽  
Retrieval Algorithm ◽  
Distribution Models ◽  
Reanalysis Dataset ◽  
The Earth ◽  
Spectrally Resolved ◽  
The Impact

&lt;p&gt;The Earth&amp;#8217;s Outgoing Longwave Radiation (OLR) is a key component in the study of climate feedbacks and processes. As part of the Earth&amp;#8217;s radiation budget, it reflects how the Earth-atmosphere system compensates the incoming solar radiation at the top of the atmosphere. It can be retrieved from the radiance intensities measured by satellite sounders and integrated over all the zenith angles of observation. Since satellite instruments generally acquire the radiance at a limited number of viewing angle directions and because the radiance field is not isotropic, the conversion is however not straightforward. This problem is usually overcome by the use of empirical angular distribution models (ADMs) developed for different scene types that directly link the directional radiance measurement to the corresponding OLR.&lt;/p&gt;&lt;p&gt;OLR estimates from dedicated broadband instruments are available since the mid-1970s; however, such instruments only provide an integrated OLR estimate over a broad spectral range. They are therefore not well suited for tracking separately the impact of the different parameters affecting the OLR (including greenhouse gases), making it difficult to track down deficiencies in climate models. Currently, several hyperspectral instruments in space acquire radiances in the thermal infrared spectral range, and in principle, these should allow to better constrain the OLR. However, as these instruments were not specifically designed to measure the OLR, there are several challenges to overcome. Here we propose a new retrieval algorithm for the estimation of the spectrally resolved OLR from measurements made by the IASI sounder on board the Metop satellites. It is based on a set of spectrally resolved ADMs developed from synthetic spectra for a large selection of scene types associated with different states of the atmosphere and the surface. Atmospheric and surface parameters are derived from the Copernicus Atmosphere Monitoring Service (CAMS) reanalysis dataset and selected using a dissimilarity-based subset selection algorithm. These spectral ADMs are then used to convert the measured IASI radiances into spectral OLR.&lt;/p&gt;&lt;p&gt;We then evaluate how the IASI OLR compare with the CERES and the AIRS integrated and spectral OLR. We analyze the interannual variations in OLR over 10 years of IASI measurements for selected spectral channels using EOF analysis and we connect them with well-known climate phenomena such as El Ni&amp;#241;o-Southern Oscillation (ENSO), the Pacific Decadal Oscillation (PDO), the Atlantic Multidecadal Oscillation (AMO).&lt;/p&gt;

scholarly journals Semiconductor light sources for near- and mid-infrared spectral ranges

2017 ◽  
Vol 917 ◽  
pp. 022003
Author(s):  
L Ya Karachinsky ◽  
A V Babichev ◽  
A G Gladyshev ◽  
D V Denisov ◽  
A V Filimonov ◽  
...  
Keyword(s):  
Light Sources ◽  
Mid Infrared ◽  
Infrared Spectral ◽  
Spectral Ranges

scholarly journals Emissivity Retrievals with FORUM's End-to-end Simulator: Challenges and Recommendations

2021 ◽  
Author(s):  
Maya Ben-Yami ◽  
Hilke Oetjen ◽  
Helen Brindley ◽  
William Cossich ◽  
Dulce Lajas ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Water Vapour ◽  
Spectral Region ◽  
Far Infrared ◽  
Spectral Emissivity ◽  
Water Vapour Content ◽  
Uncertainty Estimates ◽  
End To End ◽  
Spectrally Resolved ◽  
The Impact

Abstract. Spectral emissivity is a key property of the Earth surface of which only very few measurements exist so far in the far-infrared (FIR) spectral region, even though recent work has shown its FIR contribution is important for accurate modelling of global climate. The European Space Agency's 9th Earth Explorer, FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) will provide the first global spectrally resolved measurements of the Earth's top-of-the-atmosphere (TOA) spectrum in the FIR. In clear-sky conditions with low water vapour content, these measurements will provide a unique opportunity to retrieve spectrally resolved FIR surface emissivity. In preparation for the FORUM mission with an expected launch in 2026, this study takes the first steps towards the development of an operational emissivity retrieval for FORUM by investigating the sensitivity of the emissivity product of a full spectrum optimal estimation retrieval method to different physical and operational parameters. The tool used for the sensitivity tests is the FORUM mission's end-to-end simulator. These tests show that spectral emissivity of most surface types can be retrieved for dry scenes in the 350–600 cm−1 region with an uncertainty ranging from 0.005 to 0.01. In addition, the quality of retrieval is quantified with respect to the precipitable water vapour content of the scene, and the uncertainty caused by the correlation of emissivity with surface temperature is investigated. Two main recommendations are made based on these investigations: (1) As the extent of TOA sensitivity to the surface in the FIR depends on the atmospheric state, the spectral region of the emissivity product should be decided using a so-called information quantifier, calculated from the ratio of the retrieval uncertainty to the a-priori uncertainty. (2) Depending on retrieval input parameters, the correlation of emissivity with surface temperature allows for retrieved emissivities within a small range around the true emissivity. Thus the impact of this correlation on the uncertainty estimates of the product should be quantified in detail during further development of the operational retrieval.

scholarly journals The Effects of Surface Longwave Spectral Emissivity on Atmospheric Circulation and Convection over the Sahara and Sahel

2019 ◽  
Vol 32 (15) ◽  
pp. 4873-4890
Author(s):  
Yi-Hsuan Chen ◽  
Xianglei Huang ◽  
Xiuhong Chen ◽  
Mark Flanner
Keyword(s):  
Climate Models ◽  
Surface Air Temperature ◽  
Spectral Emissivity ◽  
Surface Emissivity ◽  
Local Climate ◽  
Spectral Bands ◽  
Simulated Precipitation ◽  
Realistic Representation ◽  
Community Earth System Model ◽  
The Impact

AbstractThis study quantifies the impact of the inclusion of realistic surface spectral emissivity in the Sahara and Sahel on the simulated local climate and beyond. The surface emissivity in these regions can be as low as 0.6–0.7 over the infrared window band while close to unity in other spectral bands, but such spectral dependence has been ignored in current climate models. Realistic surface spectral emissivities over the Sahara and Sahel are incorporated into the Community Earth System Model (CESM) version 1.1.1, while treatments of surface emissivity for the rest of the globe remain unchanged. Both the modified and standard CESM are then forced with prescribed climatological SSTs and fixed present-day forcings for 35-yr simulations. The outputs from the last 30 years are analyzed. Compared to the standard CESM, the modified CESM has warmer surface air temperature, as well as a warmer and wetter planetary boundary layer over the Sahara and Sahel. The modified CESM thus favors more convection in these regions and has more convective rainfall, especially in the Sahara. The moisture convergence induced by such inclusion of surface spectral emissivity also contributes to the differences in simulated precipitation in the Sahel and the region south to it. Compared to observations, inclusion of surface spectral emissivity reduces surface temperature biases in the Sahara and precipitation biases in the Gulf of Guinea but exacerbates the wet biases in the Sahara. Such realistic representation of surface spectral emissivity can help unmask other factors contributing to regional biases in the original CESM.

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