A fast method for the retrieval of integrated longwave and shortwave top-of-atmosphere upwelling irradiances from MSG/SEVIRI (RRUMS)

A new Rapid Retrieval of Upwelling irradiances from MSG/SEVIRI (RRUMS) is presented. It has been developed to observe the top-of-atmosphere irradiances of small scale and rapidly changing features that are not sufficiently resolved by specific Earth radiation budget sensors. Our retrieval takes advantage of the spatial and temporal resolution of MSG/SEVIRI and provides outgoing longwave and reflected shortwave radiation only by means of a combination of SEVIRI channels. The longwave retrieval is based on a simple linear combination of brightness temperatures from the SEVIRI infrared channels. The shortwave retrieval is based on a neural network that requires as input the visible and near-infrared SEVIRI channels

Estimation of land surface radiation budget from MODIS data

Land Surface Radiation Budget (SRB) is responsible for the available energy between the Earth and atmosphere system. Net radiation is the driving force for the transportation and exchange of all matter at the interface between the Earth's surface and the atmosphere, and therefore, significantly affects the climatic forming and change. Accurate estimation of shortwave net radiation (Sn), cloudy-sky allwave net radiation (Rn), and daily integrated Sn at high spatial resolution is essential in regional and global land surface models. The current SRB products have fine temporal and coarse spatial resolutions not suitable for land applications. New hybrid algorithm for Sn estimation has been developed in this study. Sn is estimated from MODIS data under both clear- and cloudy-sky conditions without requiring coarser resolution ancillary data. Therefore, estimated Sn retains the spatial resolution of the raw input data. Surface all-wave (both shortwave and longwave) net radiation (Rn) controls the input of latent and sensible heat flux into the atmosphere over the Earth's surface. Meteorological datasets are spatially limited and satellite data have the advantage of global spatial coverage; however, difficulty in accurately estimating cloudy-sky longwave net radiation (Ln) undermines efforts to estimate cloudy-sky all-wave net radiation. This study presents methods for estimating cloudy-sky Rn using Sn and other surface variables at 1 km spatial resolution. Daily integrated Sn is closely related to carbon, water and energy flux simulations. A daily integrated Sn product with a 1-km spatial resolution supports recent high resolution numerical climate and ecosystem simulations. This study describes a method for estimating daily integrated Sn in 1 km resolution based on instantaneous Sn data. All these algorithms have been validated using seven sites of a SURFace RADiation budget observing network (SURFRAD) in United States, instantaneous Sn is also compared with GEWEX/SRB and ISCCP data. The new hybrid algorithm developed in the study can be easily implemented to generate operational global products. These finer spatial resolution datasets capture the specific sequence of the redistribution of the available energy at the Earth's surface; therefore, they support recent high resolution land surface models

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

Observing the Earth radiation budget (ERB) from satellites is crucial for monitoring and understanding Earth&rsquo;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.</p

Clouds and the Earth's Radiant Energy System (CERES) Algorithm Theoretical Basis Document

The theoretical bases for the Release 1 algorithms that will be used to process satellite data for investigation of the Clouds and Earth's Radiant Energy System (CERES) are described. The architecture for software implementation of the methodologies is outlined. Volume 3 details the advanced CERES methods for performing scene identification and inverting each CERES scanner radiance to a top-of-the-atmosphere (TOA) flux. CERES determines cloud fraction, height, phase, effective particle size, layering, and thickness from high-resolution, multispectral imager data. CERES derives cloud properties for each pixel of the Tropical Rainfall Measuring Mission (TRMM) visible and infrared scanner and the Earth Observing System (EOS) moderate-resolution imaging spectroradiometer. Cloud properties for each imager pixel are convolved with the CERES footprint point spread function to produce average cloud properties for each CERES scanner radiance. The mean cloud properties are used to determine an angular distribution model (ADM) to convert each CERES radiance to a TOA flux. The TOA fluxes are used in simple parameterization to derive surface radiative fluxes. This state-of-the-art cloud-radiation product will be used to substantially improve our understanding of the complex relationship between clouds and the radiation budget of the Earth-atmosphere system

Contributions to Estimating Top-of-Atmosphere Radiative Fluxes using EarthCARE’s Broadband Radiometer

This work contributes in various ways to the estimation of top-of-atmosphere (TOA) shortwave (SW) and longwave (LW) fluxes and their uncertainties, which are based on BBR radiance measurements onboard the upcoming EarthCARE mission. We assess a so-far unaccounted sampling uncertainty of BBR-measured SW and totalwave (TW) radiances assembled towards ∼100 km² assessment domains. Uncertainties arise from irregular sampling through ∼(0.6)km² footprints within domains and a naturally heterogeneous radiance field. Sampling becomes increasingly irregular as BBR instrument performance is reduced to conserve mission lifetime. We evaluate uncertainties using Landsat 8 imagery and repeated mimicry of BBR nadir sampling under various levels of instrument performance, and measure how far BBR-obtained radiances depart from actual mean radiances over domains. We observe that uncertainty in SW and TW radiances increases linearly with radiance heterogeneity and near-linearly with reduced instrument performance. We find that the uncertainty of LW radiances, which are inferred from staggered SW and TW measurements, is particularly sensitive to instrument performance and can amount to twice the SW uncertainty – even though LW radiances are horizontally homogeneous within domains. In order to keep radiance uncertainties below a flux equivalent of 10 W/m², we recommend to reduce instrument performance no further than 25% of its nominal value. We present an algorithm for the conversion of BBR-measured TOA SW radiances into TOA SW fluxes over clear-sky domains. We find a new representation of state-of-the-art CERES angular distribution models (ADMs). Through the use of additional geophysical variables - obtained from an aerosol optical depth climatology, ERA-20C reanalysis, and climatology of MCD43BGF surface bidirectional reflectance distribution function parameters - we unite spatially and temporally separate CERES ADMs towards new ADMs per surface type and BBR-perceived scattering direction. We show which geophysical parameters are important and how well artificial neural networks perform when using essential parameters. With the exception of domains containing fresh snow, we reproduce CERES estimates with an uncertainty of 2.7 – 4.0 W/m² . Fresh snow surfaces are hardly characterized by any of above parameters and that results in larger uncertainties of 8.3 – 14.6 W/m² . We investigate whether the conversion of BBR-measured TOA SW radiances to fluxes above low-levels clouds is significantly sensitive to cloud microphysics and cloud-topped moisture. We generate new ADMs that account for cloud-top effective radii and cloud-topped water vapor by using CERES-MODIS observations and broadband simulations. We find that TOA SW anisotropy can vary by 2.9-8.0% due to extremes in cloud-top effective radii, and by 1.3-6.4% due to extremes in cloud-topped water vapor, while anisotropy uncertainty is 3.2-5.0%. Compared to state-of-the-art CERES ADMs, which lack these sensitivities, new radiance-to-flux conversions show differences of up 20 W/m² – especially for particularly small and large cloud-top effective radii (5 and 20 μm, corresponding to particularly strong and weak cloud-aerosol interaction, respectively). When applying ADMs to CERES cross-track measurements, which produce radiation budget estimates as a benchmark for global climate models, new ADMs produce TOA SW flux estimates 1-2 W/m² larger than CERES ADMs. We can attribute such flux biases in part to conditions of persistently small effective radii and low amounts of cloud-topped water vapor. This work therefore identifies additional factors impacting TOA SW anisotropy that future radiance-to-flux converting ADMs should consider to avoid sampling biases. We introduce a new method of colocating individual measurements of SW radiances and corresponding flux estimates from BBR’s three views towards a common assessment domain. By using photon paths, produced by 3D Monte-Carlo radiative transfer simulations acting on active-passive retrievals of a cloudy atmosphere, we are able to colocate even under conditions of broken and semitransparent clouds where no obvious vertical level exists that current methods would use for colocation. Applied to a 5000 km frame based on A-Train satellite observations, we find that the use of photon paths improves colocation by 4% for cirrus clouds and 15% for broken cloud fields when compared against a colocation at cloud-top height level. Once the EarthCARE mission is launched, the radiative closure assessment will compare BBR-based TOA flux estimates with simulated TOA fluxes, based on 1D or 3D radiative transfer simulations acting on active-passive retrievals of clouds and aerosols. By providing a better understanding of BBR-based TOA fluxes and their uncertainties, this work will improve the mission’s radiative closure assessment which will strengthen the science community’s understanding of the interaction among clouds, aerosols, and radiation.Die vorliegende Arbeit leistet verschiedene Beiträge zur messgestützten Schätzung von Strahlungsflüssen am Oberrand der Atmosphäre sowie deren Unsicherheiten. Die Schätzungen basieren auf Strahldichtemessungen des BBR an Bord der geplanten Satellitenmission EarthCARE. Wir untersuchen die Unsicherheiten von BBR-gemessenen Strahldichten im Nadir über 100km² großen Gebieten. Mögliche Unsicherheiten kommen durch die ungleichmäßige Erfassung (0.6km)² großer Ausleuchtbereiche innerhalb eines Gebietes und die natürliche horizontale Heterogenität des Strahlungsfeldes zustande. Ein gezieltes Herunterregeln der BBR-Leistung ermöglicht eine Verlängerung der Lebensdauer der Mission, resultiert allerdings in zunehmend ungleichmäßiger Erfassung der Strahlungsfeldes. Für diese Arbeit werden die Unsicherheiten durch Simulation verschiedener BBR-Leistungslevel an räumlich hochaufgelösten Landat-8-Messungen abgeschätzt. Die Ergebnisse zeigen, inwieweit BBR-basierte Strahldichten von eigentlichen Gebietsmitteln abweichen. Unsicherheiten kurzwelliger und totalwelliger (kurzwelliger plus langwelliger) Strahldichten nehmen linear mit der horizontalen Heterogenität des jeweiligen Strahlungsfeldes innerhalb der Gebiete zu und steigen nahezu linear mit reduzierter Leistung an. Wir zeigen weiterhin, dass langwellige Strahldichten, die von räumlich versetzten kurz- und totalwelligen Messungen abgeleitet werden, eine deutlich höhere Sensitivität gegenüber der BBR-Leistung aufweisen. Es zeigt sich eine Verdopplung der Unsicherheit von langwelligen gegenüber kurzwelligen Strahldichten, sogar wenn Gebiets-internelangwellige Strahlungsfelder horizontal homogen sind. Um eine Unsicherheit resultierender Strahlungsflüsse von unter 10 W/m² zu gewährleisten, empfehlen wir die Leistung um nicht mehr als 25% vom nominellen Wert zu reduzieren. Wir präsentieren einen Algorithmus zur Umwandlung von solaren Strahldichten in solare Strahlungsflüsse am Oberrand der Atmosphäre über wolkenfreien Gebieten. Wir zeigen eine neue Abbildung gängiger CERES Winkelverteilungsmodelle. Durch kollokierte geophysikalische Parameter (einer Klimatologie Aerosol-optischer Dicken, ERA-20C Reanalyse-Daten, sowie einer Klimatologie von MCD43BGF-basierten Parametern für bidirektionale Reflexionsverteilungsfunktionen über Landoberflächen) können räumlich und zeitlich separate CERES Modelle vereint werden, und neue Winkelverteilungsmodelle per Landoberflächenklasse und per BBR-erfassbarer Streurichtung erzeugt werden. Es wird dargestellt, welche geophysikalischen Parameter für die Erzeugung relevant sind und mit welcher Genauigkeit CERES Modelle reproduziert werden. Neue Modelle weichen um 2.7-4.0 W/m² von CERES Modellen ab, wenn Fälle mit Neuschneeereignissen ausgeschlossen werden. Neuschnee und dessen bidirektionale Reflexionsverteilung wird durch geophysikalische Parameter nicht erfasst. In diesen Fällen beträgt die Abweichung 8.3-14.6 W/m². Wir untersuchen die Umwandlung von gemessenen solaren Strahldichten in solare Strahlungsflüsse am Oberrand der Atmosphäre über tiefen Flüssigwasserwolken. Es wird die Sensitivität gegenüber der Wolkentröpfchengrößenverteilung und der Wasserdampfmenge über Wolken analysiert, die herkömmliche CERES Winkelverteilungsmodelle nicht berücksichtigen. Mit Hilfe mehrjähriger CERES-MODIS Messungen sowie Breitband-Simulationen mit dem Strahlungstransfermodell MOMO, erstellen wir neue Winkelverteilungsmodelle, die eine Sensitivität gegenüber Wolkenoberkanten-Effektivradius und Wasserdampfsäule über den Wolken zulassen. Die Ergebnisse beschreiben eine Variabilität der solaren Anisotropie von 2.9-8.0% zwischen extremen Effektivradien sowie 1.3-6.4% zwischen extremen Wasserdampfsäulengehalten. Die Unsicherheit der Anisotropie beträgt 3.2-5.0%. Im Vergleich zu CERES Winkelverteilungsmodellen weichen Strahlungsflussschätzungen um bis 20 W/m² ab. Insbesondere bei sehr kleinen und großen Effektivradien (5 und 20μm, entsprechend einer sehr starken und schwachen Wolken-Aerosol-Interaktion, respektive) wird eine große Abweichung beobachtet. Bei der Anwendung auf CERES Cross-Track Messungen, die als Grundlage zur Validierung von Klimamodellen dienen, schätzen die neu beschriebenen Winkelverteilungsmodelle 1-2 W/m² höhere solare Strahlungsflüsse als CERES Modelle. Teilweise kann diese Differenz bestimmten Regionen zugeordnet werden, die stets kleine Wolken-Effektivradien und niedrige Mengen Wolken-überlagerten Wasserdampfs ausweisen. Diese Arbeit identifiziert somit zusätzliche Anisotropie-Faktoren, die zukünftige Winkelverteilungsmodelle berücksichtigen sollten, um regionale, systematische Fehler in Strahlungsflussschätzungen zu vermeiden. Wir stellen eine neue Methode zur Kollokation von individuellen Strahldichtemessungen der drei BBR-Beobachtungsrichtungen sowie zugehörigen Strahlungsflussschätzungen zu gemeinsamen Gebieten vor. 3D Monte-Carlo Strahlungstransfersimulationen, die auf eine aktiv-passiv gemessene Atmosphäre angewendet werden, generieren Photonenpfade pro BBR-Messung. Die simulierten Photonenpfade erlauben eine Kollokation auch unter schwierigen Bedingungen, wie z.B. teilweiser oder semi-transparenter Bewölkung, an denen herkömmliche Methoden scheitern. Angewendet auf eine 5000 km lange Szene aus Satellitendaten des A-Trains, beobachten wir eine Verbesserung der Kollokation von 4% bei Zirrusbewölkung und 15% für Fälle teilweiser Bewölkung, verglichen mit einer Methode, die die Wolkenoberkantenhöhe zur Kollokation nutzt. Mit dem anstehenden Start der EarthCARE Mission wird das Strahlungsschließungsexperiment BBR-basierte und simulierter Strahlungsflüsse am Oberrand der Atmosphäre vergleichen. Durch neu gewonnene Erkenntnisse hinsichtlich BBR-gestützter Strahlungsflüsse und deren Unsicherheiten trägt diese Arbeit zum besseren Verständnis über die Wechselwirkung von Wolken, Aerosolen und Strahlung innerhalb der Wissenschaftsgemeinschaft bei

Aplikasi teknik remote sensing bagi terbitan maklumat hasilan air di Semenanjung Malaysia

Satellite remote sensing techniques have found wide applications in hydrology including water-yield determination. This however requires the localization to area-of-interest that are influenced by the local climate and biophysical factors. This study focussed to develop a method for determining the water-yield information through full satellite-based data for Peninsular Malaysia from the public domain sources, for a period of 10 years (July 2000 - June 2010). The specific objectives were to investigate on: (i) derivation of information on monthly rainfall from Tropical Rainfall Measuring Mission Multisatellite Precipitation Analysis (TMPA) satellite data; (ii) derivation of monthly Actual- Evapotranspiration (AET) from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite with Normalized Differential Vegetation Index (NDVI) data product; (iii) derivation of water yield from fully satellite-based information using water balance analysis; and (iv) water yield variation, with respect to changes of corresponding land cover and land use. Results, indicated good correlation between monthly rainfall TMPA with the corresponding rain gauge records (r2=0.71: p<0.001, n=1337) with accuracy (RMSE) of +83 mm (n=2308). The TMPAcalibrated annual averaged rainfall for the entire study area is 2357mm, which is - 5.3% compared with independent studies undertaken by an international consultant appointed by the government. The bio-physical parameters based on MODIS used NDVI as an indicator of AET to represent the land use, reported good match-up (r2=0.55: p<0.001, n=1664) with accuracy (RMSE) of +15 mm (n=864). The NDVIcalibrated annual averaged AET throughout the study area was determined at 1153mm, which is -9.9% compared with the same independent research report. Annual averaged water-yield for the entire study area is 1204mm, with -0.5% and 1.6% variations when compared to the two independent studies, the same independent research report and, Drainage and Irrigation Department respectively. But at state level, the estimated rainfall, AET and water-yield varies with larger magnitudes. Analysis at selected basin level, the annual water-yield is determined at 1393mm, in access of 9.5% compared to the independent studies water flowrate, with a standard deviation of 22%. The regression analysis between water-yield and land use cover changes, clearly indicated strong relationship (r2=0:51, p<0.0001; n=151), and independent accuracy (RMSE) of 8.3% (n=154). The main findings in this study, especially the devised techniques indeed have contributed significantly as an alternative method for the determination of water-yield in Peninsular Malaysia based on fully satellite-driven data. The devised method could be accustomized to other areas through localised calibration approach thus, could serve as a guideline for the relevant authorities to have accurate and comprehensive water-yield information

The Fifth NASA/DOD Controls-Structures Interaction Technology Conference, part 2

This publication is a compilation of the papers presented at the Fifth NASA/DoD Controls-Structures Interaction (CSI) Technology Conference held in Lake Tahoe, Nevada, March 3-5, 1992. The conference, which was jointly sponsored by the NASA Office of Aeronautics and Space Technology and the Department of Defense, was organized by the NASA Langley Research Center. The purpose of this conference was to report to industry, academia, and government agencies on the current status of controls-structures interaction technology. The agenda covered ground testing, integrated design, analysis, flight experiments and concepts