scholarly journals Shortwave Radiance to Irradiance Conversion for Earth Radiation Budget Satellite Observations: A Review

2021 ◽  
Vol 13 (13) ◽  
pp. 2640
Author(s):  
Jake J. Gristey ◽  
Wenying Su ◽  
Norman G. Loeb ◽  
Thomas H. Vonder Haar ◽  
Florian Tornow ◽  
...  
Keyword(s):  
Satellite Observations ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Distribution Models ◽  
Machine Learning Applications ◽  
Earth Radiation Budget ◽  
Scene Information ◽  
Earth’S Climate ◽  
Observational Record ◽  
Earth Radiation

Observing the Earth radiation budget (ERB) from satellites is crucial for monitoring and understanding Earth’s climate. One of the major challenges for ERB observations, particularly for reflected shortwave radiation, is the conversion of the measured radiance to the more energetically relevant quantity of radiative flux, or irradiance. This conversion depends on the solar-viewing geometry and the scene composition associated with each instantaneous observation. We first outline the theoretical basis for algorithms to convert shortwave radiance to irradiance, most commonly known as empirical angular distribution models (ADMs). We then review the progression from early ERB satellite observations that applied relatively simple ADMs, to current ERB satellite observations that apply highly sophisticated ADMs. A notable development is the dramatic increase in the number of scene types, made possible by both the extended observational record and the enhanced scene information now available from collocated imager information. Compared with their predecessors, current shortwave ADMs result in a more consistent average albedo as a function of viewing zenith angle and lead to more accurate instantaneous and mean regional irradiance estimates. One implication of the increased complexity is that the algorithms may not be directly applicable to observations with insufficient accompanying imager information, or for existing or new satellite instruments where detailed scene information is not available. Recent advances that complement and build on the base of current approaches, including machine learning applications and semi-physical calculations, are highlighted.

scholarly journals Global Daytime Mean Shortwave Flux Consistency Under Varying EPIC Viewing Geometries

2021 ◽  
Vol 2 ◽  
Author(s):  
Wenying Su ◽  
Lusheng Liang ◽  
David P. Duda ◽  
Konstantin Khlopenkov ◽  
Mandana M. Thieman
Keyword(s):  
Radiant Energy ◽  
Energy System ◽  
Field Of View ◽  
Radiation Budget ◽  
Distribution Models ◽  
The Earth ◽  
Imaging Camera ◽  
Earth Radiation Budget ◽  
Mean Square Errors ◽  
Earth Radiation

One of the most crucial tasks of measuring top-of-atmosphere (TOA) radiative flux is to understand the relationships between radiances and fluxes, particularly for the reflected shortwave (SW) fluxes. The radiance-to-flux conversion is accomplished by constructing angular distribution models (ADMs). This conversion depends on solar-viewing geometries as well as the scene types within the field of view. To date, the most comprehensive observation-based ADMs are developed using the Clouds and the Earth’s Radiant Energy System (CERES) observations. These ADMs are used to derive TOA SW fluxes from CERES and other Earth radiation budget instruments which observe the Earth mostly from side-scattering angles. The Earth Polychromatic Imaging Camera (EPIC) onboard Deep Space Climate Observatory observes the Earth at the Lagrange-1 point in the near-backscattering directions and offers a testbed for the CERES ADMs. As the EPIC relative azimuth angles change from 168◦ to 178◦, the global daytime mean SW radiances can increase by as much as 10% though no notable cloud changes are observed. The global daytime mean SW fluxes derived after considering the radiance anisotropies at relative azimuth angles of 168◦ and 178◦ show much smaller differences (<1%), indicating increases in EPIC SW radiances are due mostly to changes in viewing geometries. Furthermore, annual global daytime mean SW fluxes from EPIC agree with the CERES equivalents to within 0.5 Wm−2 with root-mean-square errors less than 3.0 Wm−2. Consistency between SW fluxes from EPIC and CERES inverted from very different viewing geometries indicates that the CERES ADMs accurately quantify the radiance anisotropy and can be used for flux inversion from different viewing perspectives.

scholarly journals Unfiltering of the Geostationary Earth Radiation Budget (GERB) Data. Part I: Shortwave Radiation

2008 ◽  
Vol 25 (7) ◽  
pp. 1087-1105 ◽  
Author(s):  
N. Clerbaux ◽  
S. Dewitte ◽  
C. Bertrand ◽  
D. Caprion ◽  
B. De Paepe ◽  
...  
Keyword(s):  
Spectral Response ◽  
Radiant Energy ◽  
Absolute Error ◽  
Energy System ◽  
Radiation Budget ◽  
Shortwave Radiation ◽  
Spectral Radiance ◽  
Visible Part ◽  
Earth Radiation Budget ◽  
Earth Radiation

Abstract The method used to estimate the unfiltered shortwave broadband radiance from the filtered radiances measured by the Geostationary Earth Radiation Budget (GERB) instrument is presented. This unfiltering method is used to generate the first released edition of the GERB-2 dataset. The method involves a set of regressions between the unfiltering factor (i.e., the ratio of the unfiltered and filtered broadband radiances) and the narrowband observations of the Spinning Enhanced Visible and Infrared Imager (SEVIRI) instrument. The regressions are theoretically derived from a large database of simulated spectral radiance curves obtained by radiative transfer computations. The generation of the database is fully described. Different sources of error that may affect the GERB unfiltering have been identified and the associated error magnitudes are assessed on this database. For most of the earth–atmosphere conditions, the error introduced during the unfiltering process is below 1%. In some conditions (e.g., low sun elevation above the horizon) the error can present a higher relative value, but the absolute error value remains well under the accuracy goal of 1% of the full instrument scale (2.4 W m−2 sr−1). To increase the confidence level, the edition 1 unfiltered radiances of GERB-2 are validated by cross comparison with collocated and coangular Clouds and the Earth’s Radiant Energy System (CERES) observations for different scene types. In addition to an overall offset between the two instruments, the intercomparisons indicate a scene-type dependency up to 4% in unfiltered radiance. Further studies are required to confirm the cause, but an insufficiently accurate characterization of the shortwave spectral response of the GERB instrument in the visible part of the spectrum is one area under further investigation.

scholarly journals Assessing the Errors in Shortwave Radiative Fluxes Inferred from the Geostationary Earth Radiation Budget (GERB) Instrument in the Presence of Dust Aerosol

2008 ◽  
Vol 47 (6) ◽  
pp. 1659-1680 ◽  
Author(s):  
Helen E. Brindley ◽  
Jacqueline E. Russell
Keyword(s):  
Angular Distribution ◽  
Specific Model ◽  
Radiation Budget ◽  
Distribution Model ◽  
Distribution Models ◽  
Radiation Fields ◽  
Time Period ◽  
Earth Radiation Budget ◽  
The Impact ◽  
Earth Radiation

Abstract The Geostationary Earth Radiation Budget (GERB) instruments flying on the Meteosat Second Generation series of satellites provide a unique tool with which to monitor the diurnal evolution of top-of-atmosphere broadband radiation fields. GERB products, which have recently been released to the scientific community, include aerosol information in addition to the observed radiances and inferred fluxes. However, no account of the anisotropic characteristics of aerosol has been incorporated in the radiance-to-flux conversion, which uses angular distribution models developed for clear or cloudy conditions. Here an attempt is made to quantify the impact of this omission in the shortwave (SW), focusing on dust-contaminated scenes. An observationally based representation of dust is used to develop a theoretical angular distribution model, which is tested through comparison with observed GERB radiances. For dusty scenes that have been processed as clear ocean, applying the dust model to convert GERB radiances to fluxes reduces the SW reflected flux by an average of approximately 12 W m−2 relative to the original GERB fluxes. This value ranges from −4 to +55 W m−2, depending on observation geometry and dust loading. For dusty scenes that the GERB processing has treated as cloudy, GERB fluxes are generally smaller than values obtained using the dust-specific model. On average, over the time period studied here, the two effects partially cancel, and the overall mean difference is 2.5 W m−2. However, it is shown that this cancellation is highly sensitive to the location and time period under consideration.

scholarly journals Radiometric and Spectral Characteristics of the ScaRaB-3 Instrument on Megha-Tropiques: Comparisons with ERBE, CERES, and GERB

2010 ◽  
Vol 27 (3) ◽  
pp. 428-442 ◽  
Author(s):  
Michel Viollier ◽  
Patrick Raberanto
Keyword(s):  
Spectral Response ◽  
Spectral Characteristics ◽  
Radiant Energy ◽  
Radiation Budget ◽  
Practical Reasons ◽  
Radiometric Calibration ◽  
Distribution Models ◽  
Earth Radiation Budget ◽  
The Difference ◽  
Earth Radiation

Abstract The Indian–French Megha-Tropiques mission, scheduled to be launched in 2010, will carry radiation and microwave sensors to study the energy and water cycle in the tropics. The radiation sensor, the third model of the Scanner for Radiation Budget (ScaRaB-3), is dedicated to the earth’s radiation budget, the difference between the solar absorbed flux and the terrestrial emitted flux. These fluxes are calculated from satellite measurements of outgoing shortwave (SW) and longwave (LW) radiances using angular distribution models (ADMs). For practical reasons, the LW radiation is calculated from the difference between a total (T) channel (0.2–100 μm) and an SW channel (0.2–4 μm). With the ADM application, the radiance calibration remains the most critical issue in the radiation budget estimation. The 1% accuracy goal is difficult to achieve, specifically in the SW domain. The authors explain their efforts to improve the radiometric calibration of ScaRaB-3. The internal calibration module is improved: the sensor is switched between SW and T channels by rotating the filter wheel on which the SW filter is now installed. Because the pyroelectric detector is sensitive to the thermal effect of the electromagnetic radiation independently of its spectral range, this plan allows calibrating the SW channel as a T channel by viewing a blackbody. Indeed, the transfer of the T calibration to the SW domain requires perfect knowledge of the total spectral response and of the transmittance of the SW filter, which is discussed in the article. Spectral errors are calculated with updated data. In the SW domain, they are found to be the smallest compared to those of the Earth Radiation Budget Experiment (ERBE), the Clouds and the Earth’s Radiant Energy System (CERES), and the Geostationary Earth Radiation Budget (GERB).

scholarly journals Unfiltering Earth Radiation Budget Experiment (ERBE) Scanner Radiances Using the CERES Algorithm and Its Evaluation with Nonscanner Observations

2014 ◽  
Vol 31 (4) ◽  
pp. 843-859 ◽  
Author(s):  
Alok K. Shrestha ◽  
Seiji Kato ◽  
Takmeng Wong ◽  
David A. Rutan ◽  
Walter F. Miller ◽  
...  
Keyword(s):  
Critical Role ◽  
Radiant Energy ◽  
Energy System ◽  
Sensitivity Study ◽  
Radiation Budget ◽  
Cloud Properties ◽  
Earth Radiation Budget ◽  
The One ◽  
Observational Record ◽  
Earth Radiation

Abstract The NOAA-9 Earth Radiation Budget Experiment (ERBE) scanner measured broadband shortwave, longwave, and total radiances from February 1985 through January 1987. These scanner radiances are reprocessed using the more recent Clouds and the Earth’s Radiant Energy System (CERES) unfiltering algorithm. The scene information, including cloud properties, required for reprocessing is derived using Advanced Very High Resolution Radiometer (AVHRR) data on board NOAA-9, while no imager data were used in the original ERBE unfiltering. The reprocessing increases the NOAA-9 ERBE scanner unfiltered longwave radiances by 1.4%–2.0% during daytime and 0.2%–0.3% during nighttime relative to those derived from the ERBE unfiltering algorithm. Similarly, the scanner unfiltered shortwave radiances increase by ~1% for clear ocean and land and decrease for all-sky ocean, land, and snow/ice by ~1%. The resulting NOAA-9 ERBE scanner unfiltered radiances are then compared with NOAA-9 nonscanner irradiances by integrating the ERBE scanner radiance over the nonscanner field of view. The comparison indicates that the integrated scanner radiances are larger by 0.9% for shortwave and 0.7% smaller for longwave. A sensitivity study shows that the one-standard-deviation uncertainties in the agreement are ±2.5%, ±1.2%, and ±1.8% for the shortwave, nighttime longwave, and daytime longwave irradiances, respectively. The NOAA-9 and ERBS nonscanner irradiances are also compared using 2 years of data. The comparison indicates that the NOAA-9 nonscanner shortwave, nighttime longwave, and daytime longwave irradiances are 0.3% larger, 0.6% smaller, and 0.4% larger, respectively. The longer observational record provided by the ERBS nonscanner plays a critical role in tying the CERES-like NOAA-9 ERBE scanner dataset from the mid-1980s to the present-day CERES scanner data record.

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