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 FORUM Earth Explorer 9: Characteristics of Level 2 Products and Synergies with IASI-NG

2020 ◽  
Vol 12 (9) ◽  
pp. 1496
Author(s):  
Marco Ridolfi ◽  
Samuele Del Bianco ◽  
Alessio Di Roma ◽  
Elisa Castelli ◽  
Claudio Belotti ◽  
...  
Keyword(s):  
Water Vapour ◽  
Far Infrared ◽  
Spectral Emissivity ◽  
Spectral Radiance ◽  
Calibration Error ◽  
Water Path ◽  
Cloud Parameters ◽  
Ice Water Path ◽  
Ice Water ◽  
Level 2

FORUM (Far-infrared Outgoing Radiation Understanding and Monitoring) has been approved to be the ninth Earth Explorer mission of the European Space Agency. The mission is scheduled for launch on a Polar satellite in the 2025–2026 time frame. The core FORUM instrument is a Fourier Transform Spectrometer measuring, with very high accuracy, the upwelling spectral radiance, from 100 to 1600 cm − 1 (from 100 to 6.25 microns in wavelength), thus covering the Far-Infrared (FIR), and a Mid-Infrared (MIR) portion of the spectrum emitted by the Earth. FORUM will fly in loose formation with the MetOp-SG-1A satellite, hosting the Infrared Atmospheric Sounding Interferometer – New Generation (IASI-NG). IASI-NG will measure only the MIR part of the upwelling atmospheric spectrum, from 645 to 2760 cm − 1 (from 15.5 to 3.62 microns in wavelength), thus, the matching FORUM measurements will supply the missing FIR complement. Together, the two missions will provide, for the first time, a spectrally resolved measurement of the full Earth emitted thermal spectrum. The calibrated spectral radiance will be, on its own, the main product of the FORUM mission, however, the radiances will also be processed up to Level 2, to determine the vertical profile of water vapour, surface spectral emissivity and cloud parameters in the case of cloudy atmospheres. In this paper we assess the performance of the FORUM Level 2 products based on clear-sky simulated retrievals and we study how the FORUM and IASI-NG matching measurements can be fused in a synergistic retrieval scheme, to provide improved Level 2 products. Considering only the measurement noise and the systematic calibration error components, we find the following figures for the synergistic FORUM and IASI-NG retrieval products. In the upper troposphere/lower stratosphere region, individual water vapour profiles can be retrieved with 1 km vertical sampling and an error ranging from 10% to 15%. In the range from 300 to 600 cm − 1 , surface spectral emissivity can be retrieved with an absolute error as small as 0.001 in dry Polar atmospheres. Ice cloud parameters such as ice water path and cloud top height can be retrieved with errors smaller than 10% and 1 km, respectively, for ice water path values ranging from 0.2 to 60 g/m 2 .

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 The impact of deforestation in the Amazonian atmospheric radiative balance: a remote sensing assessment

2012 ◽  
Vol 12 (6) ◽  
pp. 14837-14874 ◽  
Author(s):  
E. T. Sena ◽  
P. Artaxo ◽  
A. L. Correia
Keyword(s):  
Water Vapour ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Radiative Effect ◽  
Water Vapour Content ◽  
Albedo Change ◽  
Direct Radiative Forcing ◽  
The Mean ◽  
The Impact

Abstract. This paper addresses the Amazonian radiative budget after considering three aspects of deforestation: (i) the emission of aerosols from biomass burning due to forest fires; (ii) changes in surface albedo after deforestation and (iii) modifications in the column water vapour amount over deforested areas. Simultaneous Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging SpectroRadiometer (MODIS) were analysed during the peak of the biomass burning seasons (August and September) from 2000 to 2009. A discrete-ordinate radiative transfer (DISORT) code was used to extend instantaneous remote sensing radiative forcing assessments into 24-h averages. The mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season for the 10-yr studied period was −5.6 ± 1.7 W m−2. Furthermore, the spatial distribution of the direct radiative forcing of aerosols over Amazon was obtained for the biomass burning season of each year. It was observed that for high AOD (larger than 1 at 550 nm) the imbalance in the radiative forcing at the TOA may be as high as −20 W m−2 locally. The surface reflectance plays a major role in the aerosol direct radiative effect. The study of the effects of biomass burning aerosols over different surface types shows that the direct radiative forcing is systematically more negative over forest than over savannah-like covered areas. Values of −15.7 ± 2.4 W m−2/τ550 nm and −9.3 ± 1.7 W m−2/τ550 nm were calculated for the mean daily aerosol forcing efficiencies over forest and savannah-like vegetation respectively. The overall mean annual albedo-change radiative forcing due to deforestation over the state of Rondônia, Brazil, was determined as −7.3 ± 0.9 W m−2. Biomass burning aerosols impact the radiative budget for approximately two months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo-change is approximately 6 times higher than the impact due to aerosol emissions. The influence of atmospheric water vapour content in the radiative budget was also studied using AERONET column water vapour. It was observed that column water vapour is in average smaller by about 0.35 cm over deforested areas compared to forested areas. Our results indicate that this drying impact contributes to an increase in the shortwave radiative effect that varies from 0.4 W m−2 to 1.2 W m−2, depending on the column water vapour content before deforestation. The large radiative forcing values presented in this study point out that deforestation has strong implications in convection, cloud development and photosynthesis rate over the Amazon region.

Retrieval of Stable Water Vapour Isotopologues from the TROPOMI Instrument

2021 ◽  
Author(s):  
Tim Trent ◽  
Hartmut Boesch ◽  
Peter Somkuti ◽  
Mathhias Schneider ◽  
Farahnaz Khosrawi ◽  
...  
Keyword(s):  
Water Vapour ◽  
In Situ Measurements ◽  
Climate Feedback ◽  
Retrieval Algorithm ◽  
Unique Contribution ◽  
Water Vapour Content ◽  
Infrared Measurements ◽  
Water Isotopologues ◽  
The Impact

&lt;p&gt;Atmospheric moisture is a crucial factor for the redistribution of heat in the atmosphere, with a strong coupling between atmospheric circulation and moisture pathways responsible most climate feedback mechanisms. Conventional satellite and in situ measurements provide information on water vapour content and vertical distribution; however, observations of water isotopologues make a unique contribution to a better understanding of this coupling.&lt;/p&gt;&lt;p&gt;In recent years, observations of water vapour isotopologue from satellites have become available from nadir thermal infrared measurements (TES, AIRS, IASI) which are sensitive to the free troposphere and from shortwave-infrared (SWIR) sensors (GOSAT, SCIAMACHY) that provide column-averaged concentrations including sensitivity to the boundary layer. The TROPOMI instrument on-board Sentinel 5P (S5p) measures SWIR radiance spectra that allow retrieval of water isotopologue columns but with much improved spatial and temporal coverage compared to other SWIR sensors promising a step-change for scientific and operational applications.&lt;/p&gt;&lt;p&gt;Here we present the retrieval algorithm development for stable water isotopologues from TROPOMI as part of the ESA S5p Innovation programme.&amp;#160; We also discuss the validation of these types of satellite products with fiducial in situ measurements, and challenges compared with other satellite measurements. Finally, we outline the roadmap for assessing the impact of TROPOMI data against state-of-the-art isotope enabled models.&lt;/p&gt;

scholarly journals Spatial variability of the direct radiative forcing of biomass burning aerosols and the effects of land use change in Amazonia

2013 ◽  
Vol 13 (3) ◽  
pp. 1261-1275 ◽  
Author(s):  
E. T. Sena ◽  
P. Artaxo ◽  
A. L. Correia
Keyword(s):  
Land Use ◽  
Land Use Change ◽  
Water Vapour ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Surface Albedo ◽  
Water Vapour Content ◽  
Direct Radiative Forcing ◽  
The Mean ◽  
The Impact

Abstract. This paper addresses the Amazonian shortwave radiative budget over cloud-free conditions after considering three aspects of deforestation: (i) the emission of aerosols from biomass burning due to forest fires; (ii) changes in surface albedo after deforestation; and (iii) modifications in the column water vapour amount over deforested areas. Simultaneous Clouds and the Earth's Radiant Energy System (CERES) shortwave fluxes and aerosol optical depth (AOD) retrievals from the Moderate Resolution Imaging SpectroRadiometer (MODIS) were analysed during the peak of the biomass burning seasons (August and September) from 2000 to 2009. A discrete-ordinate radiative transfer (DISORT) code was used to extend instantaneous remote sensing radiative forcing assessments into 24-h averages. The mean direct radiative forcing of aerosols at the top of the atmosphere (TOA) during the biomass burning season for the 10-yr studied period was −5.6 ± 1.7 W m−2. Furthermore, the spatial distribution of the direct radiative forcing of aerosols over Amazonia was obtained for the biomass burning season of each year. It was observed that for high AOD (larger than 1 at 550 nm) the maximum daily direct aerosol radiative forcing at the TOA may be as high as −20 W m−2 locally. The surface reflectance plays a major role in the aerosol direct radiative effect. The study of the effects of biomass burning aerosols over different surface types shows that the direct radiative forcing is systematically more negative over forest than over savannah-like covered areas. Values of −15.7 ± 2.4 W m−2τ550 nm and −9.3 ± 1.7 W m−2τ550 nm were calculated for the mean daily aerosol forcing efficiencies over forest and savannah-like vegetation respectively. The overall mean annual land use change radiative forcing due to deforestation over the state of Rondônia, Brazil, was determined as −7.3 ± 0.9 W m−2. Biomass burning aerosols impact the radiative budget for approximately two months per year, whereas the surface albedo impact is observed throughout the year. Because of this difference, the estimated impact in the Amazonian annual radiative budget due to surface albedo-change is approximately 6 times higher than the impact due to aerosol emissions. The influence of atmospheric water vapour content in the radiative budget was also studied using AERONET column water vapour. It was observed that column water vapour is on average smaller by about 0.35 cm (around 10% of the total column water vapour) over deforested areas compared to forested areas. Our results indicate that this drying contributes to an increase in the shortwave radiative forcing, which varies from 0.4 W m−2 to 1.2 W m−2 depending on the column water vapour content before deforestation. The large radiative forcing values presented in this study point out that deforestation could have strong implications in convection, cloud development and the ratio of direct to diffuse radiation, which impacts carbon uptake by the forest.

scholarly journals Measurement of the water vapour vertical profile and of the Earth's outgoing far infrared flux

2008 ◽  
Vol 8 (11) ◽  
pp. 2885-2894 ◽  
Author(s):  
L. Palchetti ◽  
G. Bianchini ◽  
B. Carli ◽  
U. Cortesi ◽  
S. Del Bianco
Keyword(s):  
Water Vapour ◽  
Far Infrared ◽  
Radiation Budget ◽  
Accurate Information ◽  
Spectral Radiation ◽  
Uncooled Detectors ◽  
Upper Troposphere ◽  
Atmospheric State ◽  
Spectrally Resolved ◽  
Earth’S Radiation Budget

Abstract. Our understanding of global warming depends on the accuracy with which the atmospheric components that modulate the Earth's radiation budget are known. Many uncertainties still exist as regards the radiative effect of water in the different spectral regions, among which is the far infrared, where very few observations have been made. An assessment is shown of the atmospheric outgoing flux obtained from a balloon-borne platform with wideband spectrally-resolved nadir measurements at the top of the atmosphere over the full spectral range, from 100 to 1400 cm−1, made by a Fourier transform spectrometer with uncooled detectors. From these measurements, we retrieved 15 pieces of information regarding water vapour and temperature profiles and surface temperature, with a major improvement in our knowledge of water vapour in the upper troposphere. The retrieved atmospheric state made it possible to calculate the emitted radiance also at frequencies and zenith angles that have not been observed and to determine the outgoing spectral radiation flux. This proves that spectrally resolved observations can be used to derive accurate information on the integrated flux. While the retrieved temperature was in agreement with ECMWF analysis, the retrieved water vapour profile differed significantly; depending on the time and the location, the derived flux in the far infrared (20–600 cm−1) differed by 2–3.5 W/m2 from that calculated using ECMWF. The error with which the far infrared flux is determined by REFIR-PAD is about 0.4 W/m2 and is caused mainly by calibration uncertainties, while detector noise has a negligible effect. This proves that uncooled detectors are adequate for top-of-the-atmosphere radiometry.

The Novel Heating Method for the Sample of Spectral Emissivity Measurement

2011 ◽  
Vol 148-149 ◽  
pp. 951-957 ◽  
Author(s):  
Li Xing ◽  
Zun Dong Yuan ◽  
Min Chen Guo ◽  
Dong Wei ◽  
Li Zhi Cai ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Surface Temperature ◽  
Spectral Emissivity ◽  
The Novel ◽  
Heating Method ◽  
Low Thermal Conductivity ◽  
Measurement Results ◽  
Potential Applications ◽  
Emissivity Measurement ◽  
The Impact

In order to eliminate the temperature difference between center measurement points and surface temperature of the material samples with low thermal conductivity, this paper introduces a new hot airflow double-sided heating method for sample, and describes its principle, application, and the impact of the existing and novel methods on the measurement results of spectral emissivity. Also, we analyze and compare the results of two different samples obtained with these two heating methods. The new method for material samples with low thermal conductivity has outstanding advantages and potential applications.

scholarly journals Measurement of the water vapour vertical profile and of the Earth's outgoing far infrared flux

2007 ◽  
Vol 7 (6) ◽  
pp. 17741-17767 ◽  
Author(s):  
L. Palchetti ◽  
G. Bianchini ◽  
B. Carli ◽  
U. Cortesi ◽  
S. Del Bianco
Keyword(s):  
Water Vapour ◽  
Radiative Forcing ◽  
Far Infrared ◽  
Radiation Budget ◽  
Accurate Information ◽  
Uncooled Detectors ◽  
The Mean ◽  
Spectrally Resolved ◽  
Earth’S Radiation Budget ◽  
Good Agreement

Abstract. Our understanding of global warming depends on the accuracy with which the atmospheric components that modulate the Earth's radiation budget are known. Many uncertainties still exist on the radiative effect of water in the different spectral regions, among which the far infrared where few observations have been made. An assessment is shown of the atmospheric outgoing flux obtained from a balloon-borne platform with wideband spectrally resolved nadir measurements at the top-of-atmosphere over the full spectral range, including the far infrared, from 100 to 1400 cm−1, made by a Fourier transform spectrometer with uncooled detectors. From these measurements, we retrieve 15 pieces of information about water vapour and temperature profiles, and surface temperature, with a precision of 5% for the mean water vapour profile and a major improvement of the upper troposphere-lower stratosphere knowledge. The retrieved atmospheric state makes it possible to calculate the emitted radiance as a function of the zenith angle and to determine the outgoing radiation flux, proving that spectrally resolved observations can be used to derive accurate information on the integrated flux. While the retrieved temperature is in good agreement with ECMWF analysis, the retrieved water vapour profile differs significantly, and, depending on time and location, the derived flux differs in the far infrared (0–600 cm−1) from that derived from ECMWF by 2–3.5 W/m2±0.4 W/m2. The observed discrepancy is larger than current estimates of radiative forcing due to CO2 increases since pre-industrial time. The error with which the flux is determined is caused mainly by calibration uncertainties while detector noise has a negligible effect, proving that uncooled detectors are adequate for top of the atmosphere radiometry.

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