852 research outputs found

    Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks

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    This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.The AERONET Cimel sun photometer at Izaña has been calibrated by AERONET-EUROPE Calibration Service, financed by the Aerosol Cloud and TRace gas InfraStructure (ACTRIS) European Research Infrastructure Action (FP7/2007-2013 no. 262254). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) and from the “Fondo Europeo de Desarrollo Regional” (FEDER) for project CGL2012-33576 is gratefully acknowledged

    Collinsville solar thermal project: yield forecasting (draft report)

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    The final report has been published and is available here. Executive Summary 1        Introduction This report’s primary aim is to provide yield projections for the proposed Linear Fresnel Reflector (LFR) technology plant at Collinsville, Queensland, Australia.  However, the techniques developed in this report to overcome inadequate datasets at Collinsville to produce the yield projections are of interest to a wider audience because inadequate datasets for renewable energy projects are commonplace.  The subsequent report called ‘Energy economics and dispatch forecasting’ (Bell, Wild & Foster 2014a) uses the yield projections from this report to produce long-term wholesale market price and dispatch forecasts for the plant.  2        Literature review The literature review discusses the four drivers for yield for LFR technology: DNI (Direct Normal Irradiance) Temperature Humidity Pressure Collinsville lacks complete historical datasets of the four drivers to develop yield projects but its three nearby neighbours do possess complete datasets, so could act as proxies for Collinsville.  However, analysing the four drivers for Collinsville and its three nearby sites shows that there is considerable difference in their climates.  This difference makes them unsuitable to act as proxies for yield calculations.  Therefore, the review investigates modelling the four drivers for Collinsville. We introduce the term “effective” DNI to help clarify and ameliorate concerns over the dust and dew effects on terrestrial DNI measurement and LFR technology. We also introduce a modified TMY technique to overcome technology specific Typical Metrological Year (TMY).  We discuss the effect of climate change and the El Nino Southern Oscillation (ENSO) on yield and their implications for a TMY. 2.1     Research questions Research question arising from the literature review include: The overarching research question: Can modelling the weather with limited datasets produce greater yield predictive power than using the historically more complete datasets from nearby sites? This overarching question has a number of smaller supporting research questions: Is BoM’s DNI satellite dataset adequately adjusted for cloud cover at Collinsville? Given the dust and dew effects, is using raw satellite data sufficient to model yield? Does elevation between Collinsville and nearby sites affect yield? How does the ENSO affect yield? Given the 2007-2012 constraint, will the TMY process provide a “Typical” year over the ENSO cycle? How does climate change affect yield? A further research question arises in the methodology but is included here for completeness. What is the expected frequency of oversupply from the Linear Fresnel Novatec Solar Boiler? 3        Methodology In the methodology section, we discuss the data preparation and the model selection process for the four drivers of yield. 4        Results and analysis In the results section we present the four driver models selected and the process that was undertaken to arrive at the models. 5        Discussion We analyse the extent to which the research questions are informed by the results. 6        Conclusion In this report, we have identified the key research questions and established a methodology to address these questions.  The models for the four drivers have been established allowing the calculation of the yield projections for Collinsville

    Aerosol optical depth retrievals at the Izaña Atmospheric Observatory from 1941 to 2013 by using artificial neural networks [Discussion paper]

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    This paper presents the reconstruction of a 73-year time series of the aerosol optical depth (AOD) at 500 nm at the subtropical high-mountain Izaña Atmospheric Observatory (IZO) located in Tenerife (Canary Islands, Spain). For this purpose, we have combined AOD estimates from artificial neural networks (ANNs) from 1941 to 2001 and AOD measurements directly obtained with a Precision Filter Radiometer (PFR) between 2003 and 2013. The analysis is limited to summer months (July–August–September), when the largest aerosol load is observed at IZO (Saharan mineral dust particles). The ANN AOD time series has been comprehensively validated against coincident AOD measurements performed with a solar spectrometer Mark-I (1984–2009) and AERONET (AErosol RObotic NETwork) CIMEL photometers (2004–2009) at IZO, obtaining a rather good agreement on a daily basis: Pearson coefficient, R, of 0.97 between AERONET and ANN AOD, and 0.93 between Mark-I and ANN AOD estimates. In addition, we have analysed the long-term consistency between ANN AOD time series and long-term meteorological records identifying Saharan mineral dust events at IZO (synoptical observations and local wind records). Both analyses provide consistent results, with correlations  >  85 %. Therefore, we can conclude that the reconstructed AOD time series captures well the AOD variations and dust-laden Saharan air mass outbreaks on short-term and long-term timescales and, thus, it is suitable to be used in climate analysis.The AERONET Cimel sun photometer at Izaña has been calibrated by AERONET-EUROPE Calibration Service, financed by the Aerosol Cloud and TRace gas InfraStructure (ACTRIS) European Research Infrastructure Action (FP7/2007-2013 no. 262254). Financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) and from the “Fondo Europeo de Desarrollo Regional” (FEDER) for project CGL2012-33576 is gratefully acknowledged

    Arctic low-level mixed-phase clouds and their complex interactions with aerosol and radiation: Remote sensing of the Arctic troposphere with the shipborne supersite OCEANET-Atmosphere

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    In the course of this thesis, Arctic low-level mixed-phase clouds and their interaction with aerosol and radiation have been investigated. To do so, measurements with the shipborne remote sensing supersite OCEANET-Atmosphere were conducted during the PS106 expedition in the Arctic summer 2017. OCEANET-Atmosphere comprises among other instruments a multiwavelength polarization lidar PollyXT and a microwave radiometer HATPRO. For PS106 the OCEANET-Atmosphere facility was complemented for the first time with a motion-stabilized vertically pointing Doppler cloud radar Mira-35. The cloud radar Doppler velocity was corrected for the ship’s vertical movement. The stabilization and the correction enabled, e.g., the derivation of eddy dissipation rates from the Doppler velocities. A data set of cloud microphysical and macrophysical properties was derived by applying the synergistic Cloudnet algorithm to the combined measurements of cloud radar, lidar, and microwave radiometer. Within this thesis, the set of the Cloudnet retrievals was improved to account for the complex structure of the Arctic cloud system. A new detection approach for the frequently observed low-level stratus clouds was developed based on the lidar signal-to-noise ratio. These clouds, which were below the lowest range gate of the cloud radar were observed during 50 % of the observational time. A new approach for the continuous determination of the ice crystal effective radius was introduced. This new retrieval made the data set suitable to perform high-resolved radiative transfer simulations. The retrieved data set was utilized to derive the first temperature relationship for heterogeneous ice formation in Arctic mixed-phase clouds. A strong dependence of the surface coupling state for high subzero ice-formation temperatures was found. For an ice-formation temperature above -15 °C, surface-coupled ice-containing clouds occur more frequently by a factor of 5 in numbers of observed clouds and by a factor of 2 in frequency of occurrence. Possible causes of the observed effect were discussed by sensitivity studies and a literature survey. Instrumental and methodological effects, and previously published similar observations of an increased ice occurrence at such high subzero temperatures have been ruled out as a possible explanation. The most likely cause of the observed effect was attributed to a larger reservoir of biogenic ice-nucleating particles in the surface-coupled marine boundary layer. This larger reservoir led to a higher freezing efficiency in these clouds which had at least their base in that layer. Finally, the importance of the detailed classification of the low-level clouds was highlighted by the evaluation of radiative transfer simulations. A difference in the cloud radiative effect of up to 100 W m-2 was calculated when these clouds were considered.:1 Introduction 2 Arctic — Amplified climate change 2.1 The Arctic climate system 2.2 Cloud radiation budget 2.3 Arctic mixed-phase clouds 2.4 Heterogeneous ice formation in Arctic mixed-phase clouds — constraints and previous findings 2.5 Motivating research questions 3 Data set — Applied instrumentation, processing, and retrievals 3.1 Introduction to ground-based active remote sensing of aerosol and clouds 3.1.1 Lidar principle 3.1.2 Radio Detection and Ranging — Radar 3.2 The Arctic expedition PS106 3.3 Instrumentation 3.3.1 The OCEANET-Atmosphere observatory 3.3.2 Other instruments used in this study 3.4 Data processing and synergistic retrievals 3.4.1 Correction of vertical-stare cloud radar observations for ship motion 3.4.2 Retrieval of eddy dissipation rate from Doppler radar spectra 3.4.3 Cloud macro- and microphysical properties from instrument-synergies 3.5 Summary of the data processing for PS106 4 Cloud and aerosol observations during PS106 4.1 Meteorological conditions during PS106 4.2 Case studies 4.3 Cloud and aerosol statistics during PS106 4.4 Discussion of the observational data sets 5 Contrasting surface-coupling effects on heterogeneous ice formation 5.1 Methodology 5.1.1 Ice-containing cloud analysis 5.1.2 Surface-coupling state 5.2 Results: influence of surface coupling on heterogeneous ice formation temperature 5.3 Discussion of the observed surface-coupling effects 5.3.1 Methodological and instrumental effects 5.3.2 Possible causes for increased ice occurrence in surface-coupled clouds 6 Application of the data set in collaborative studies and radiative transfer simulations within (AC)3 6.1 Radiative transfer simulations and cloud radiative effect 6.2 LLS treatment for improved radiative transfer simulations 6.3 Discussion 7 Summary and outlook Appendices A Determination of a volume depolarization threshold forlidar-based ice detection BibliographyIm Rahmen dieser Arbeit wurden niedrige arktische Mischphasenwolken und ihre Wechselwirkung mit Aerosolen und Strahlung untersucht. Dazu wurden Messungen mit der schiffsgestĂŒtzten Fernerkundungs-Supersite OCEANET-Atmosphere wĂ€hrend der PS106-Expedition im arktischen Sommer 2017 durchgefĂŒhrt. OCEANET-Atmosphere vereint, u.a., ein MultiwellenlĂ€ngen-Polarisations-Lidar PollyXT und ein Mikrowellen-Radiometer HATPRO. FĂŒr PS106 wurde OCEANET-Atmosphere erstmalig um ein stabilisiertes, vertikal ausgerichtetes Doppler-Wolkenradar Mira-35 erweitert. Die Doppler-Geschwindigkeit wurde in Bezug auf die Vertikalbewegung des Schiffes korrigiert. Dank Stabilisierung und Korrektur war, z.B., die Ableitung von Wirbeldissipationsraten aus den Doppler-Geschwindigkeiten möglich. Unter Anwendung des synergetischen Cloudnet-Algorithmus wurde aus den kombinierten Wolkenradar, Lidar und Mikrowellenradiometer Messungen ein Datensatz der mikro- und makrophysikalischen Wolkeneigenschaften fĂŒr PS106 erstellt. Im Rahmen dieser Arbeit wurde Cloudnet verbessert, um der komplexen Struktur der arktischen Wolken Rechnung zu tragen. Ein neuer Ansatz zur Erkennung der hĂ€ufig beobachteten niedrigen Stratuswolken wurde entwickelt, basierend auf dem Lidar-Signal-zu-Rausch-VerhĂ€ltnis. Diese Wolken, die unterhalb des untersten Höhenlevels des Wolkenradars auftraten, wurden wĂ€hrend 50% der Beobachtungszeit identifiziert. Ein neuer Ansatz fĂŒr die kontinuierliche Bestimmung des effektiven Radius der Eiskristalle wurde eingefĂŒhrt. Dank dieser neuen Methode eignet sich der erstellte Datensatz fĂŒr die DurchfĂŒhrung von Strahlungstransfersimulationen. Zum ersten Mal wurde eine Temperaturbeziehung fĂŒr heterogene Eisbildung in arktischen Mischphasenwolken in AbhĂ€ngigkeit ihres OberflĂ€chen-Kopplungsstatus abgeleitet. Bei Temperaturen ĂŒber -15°C war die relative HĂ€ufigkeit von Eis beinhaltenden Wolken doppelt so hoch und die Anzahl fĂŒnf Mal höher wenn sie mxit der OberflĂ€che gekoppelt waren, als bei entkoppelte Wolken. Mögliche Ursachen fĂŒr den beobachteten Effekt wurden anhand von SensitivitĂ€tsstudien und einer Literaturanalyse diskutiert. Instrumentelle und methodische Effekte sowie frĂŒher veröffentlichte Ă€hnliche Beobachtungen konnten als mögliche ErklĂ€rung ausgeschlossen werden. Die wahrscheinlichste Ursache fĂŒr den beobachteten Effekt wurde auf ein grĂ¶ĂŸeres Reservoir an biogenen Eiskristallisationskeimen in der oberflĂ€chengekoppelten marinen Grenzschicht zurĂŒckgefĂŒhrt. Dieses grĂ¶ĂŸere Reservoir hat zu einer höheren Gefriereffizienz in Wolken gefĂŒhrt, die zumindest ihre Basis in dieser Schicht hatten. Die Bedeutung der detaillierten Klassifizierung von tiefliegenden Wolken auf Strahlungstransfersimulationen wurde hervorgehoben. Der simulierte Effekt der Wolken auf den Strahlungshaushalt unterschied sich bis zu 100 W m-2, unter BerĂŒcksichtigung dieser Wolken.:1 Introduction 2 Arctic — Amplified climate change 2.1 The Arctic climate system 2.2 Cloud radiation budget 2.3 Arctic mixed-phase clouds 2.4 Heterogeneous ice formation in Arctic mixed-phase clouds — constraints and previous findings 2.5 Motivating research questions 3 Data set — Applied instrumentation, processing, and retrievals 3.1 Introduction to ground-based active remote sensing of aerosol and clouds 3.1.1 Lidar principle 3.1.2 Radio Detection and Ranging — Radar 3.2 The Arctic expedition PS106 3.3 Instrumentation 3.3.1 The OCEANET-Atmosphere observatory 3.3.2 Other instruments used in this study 3.4 Data processing and synergistic retrievals 3.4.1 Correction of vertical-stare cloud radar observations for ship motion 3.4.2 Retrieval of eddy dissipation rate from Doppler radar spectra 3.4.3 Cloud macro- and microphysical properties from instrument-synergies 3.5 Summary of the data processing for PS106 4 Cloud and aerosol observations during PS106 4.1 Meteorological conditions during PS106 4.2 Case studies 4.3 Cloud and aerosol statistics during PS106 4.4 Discussion of the observational data sets 5 Contrasting surface-coupling effects on heterogeneous ice formation 5.1 Methodology 5.1.1 Ice-containing cloud analysis 5.1.2 Surface-coupling state 5.2 Results: influence of surface coupling on heterogeneous ice formation temperature 5.3 Discussion of the observed surface-coupling effects 5.3.1 Methodological and instrumental effects 5.3.2 Possible causes for increased ice occurrence in surface-coupled clouds 6 Application of the data set in collaborative studies and radiative transfer simulations within (AC)3 6.1 Radiative transfer simulations and cloud radiative effect 6.2 LLS treatment for improved radiative transfer simulations 6.3 Discussion 7 Summary and outlook Appendices A Determination of a volume depolarization threshold forlidar-based ice detection Bibliograph

    Very short-term photovoltaic power forecasting with cloud modeling: A review

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    This paper endeavors to provide the reader with an overview of the various tools needed to forecast photovoltaic (PV) power within a very short-term horizon. The study focuses on the specific application of a large scale grid-connected PV farm. Solar resource is largely underexploited worldwide whereas it exceeds by far humans' energy needs. In the current context of global warming, PV energy could potentially play a major role to substitute fossil fuels within the main grid in the future. Indeed, the number of utility-scale PV farms is currently fast increasing globally, with planned capacities in excess of several hundred megawatts. This makes the cost of PV-generated electricity quickly plummet and reach parity with non-renewable resources. However, like many other renewable energy sources, PV power depends highly on weather conditions. This particularity makes PV energy difficult to dispatch unless a properly sized and controlled energy storage system (ESU) is used. An accurate power forecasting method is then required to ensure power continuity but also to manage the ramp rates of the overall power system. In order to perform these actions, the forecasting timeframe also called horizon must be first defined according to the grid operation that is considered. This leads to define both spatial and temporal resolutions. As a second step, an adequate source of input data must be selected. As a third step, the input data must be processed with statistical methods. Finally, the processed data are fed to a precise PV model. It is found that forecasting the irradiance and the cell temperature are the best approaches to forecast precisely swift PV power fluctuations due to the cloud cover. A combination of several sources of input data like satellite and land-based sky imaging also lead to the best results for very-short term forecasting

    Novel atmospheric extinction measurement techniques for aerospace laser system applications

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    Novel techniques for laser beam atmospheric extinction measurements, suitable for manned and unmanned aerospace vehicle applications, are presented in this paper. Extinction measurements are essential to support the engineering development and the operational employment of a variety of aerospace electro-optical sensor systems, allowing calculation of the range performance attainable with such systems in current and likely future applications. Such applications include ranging, weaponry, Earth remote sensing and possible planetary exploration missions performed by satellites and unmanned flight vehicles. Unlike traditional LIDAR methods, the proposed techniques are based on measurements of the laser energy (intensity and spatial distribution) incident on target surfaces of known geometric and reflective characteristics, by means of infrared detectors and/or infrared cameras calibrated for radiance. Various laser sources can be employed with wavelengths from the visible to the far infrared portions of the spectrum, allowing for data correlation and extended sensitivity. Errors affecting measurements performed using the proposed methods are discussed in the paper and algorithms are proposed that allow a direct determination of the atmospheric transmittance and spatial characteristics of the laser spot

    Assessment of Weather Sensitivities and Air Force Weather (AFW) Support to Tactical Lasers in the Lower Troposphere

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    ATL scientists need to develop a full understanding of the interaction effects between a high-energy laser beam and the atmosphere through which it propagates. Achieving this understanding is important for many reasons. In particular, the high cost of DE weapons systems makes each propagation event expensive. Having an understanding of the atmosphere in which a high-energy laser propagates will increase efficiency and effectiveness of the ATL weapon system, which in turn will decrease cost of operation. A tool that allows for the ATL war-fighter to determine the atmospheric effects on laser propagation currently does not exist. This study creates a stepping-stone toward creating a High Energy Laser Tactical Decision Aid (HELTDA) in which the war-fighter will be able to determine the effectiveness of the ATL weapon system with accuracy in order to maximize efficiency in a specific environment. Using the High Energy Laser End-to-End Simulation (HELEEOS) software, comparisons are made across various atmospheric factors. These factors consist of a variety of turbulence and wind profiles, aerosol effects, time of day, clouds and rain, and relative humidity, which are compared for summer and winter for a specific mid-latitude geographic location. In addition, the atmospheric factors run in HELEEOS are used to determine and characterize the relevant attenuating factors of extinction and thermal blooming, which are inferred by the different engagement scenarios tested. The results illustrate the three attenuation factors of high energy laser propagation: optical turbulence, extinction, and thermal blooming. In this study, the most significant attenuation factor is thermal blooming. Extinction is a significant attenuator as well, however, not to the degree of thermal blooming. Optical turbulence proved to be a negligible attenuator for increasingly vertical engagements. This is especially true for ATL engagements, which are generally limited to approximately 10km in slant range. The seasonal and time of day weather effects are also at times significant

    Airborne laser systems for atmospheric sounding in the near infrared

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    This paper presents new techniques for atmospheric sounding using Near Infrared (NIR) laser sources, direct detection electro-optics and passive infrared imaging systems. These techniques allow a direct determination of atmospheric extinction and, through the adoption of suitable inversion algorithms, the indirect measurement of some important natural and man-made atmospheric constituents, including Carbon Dioxide (CO2). The proposed techniques are suitable for remote sensing missions performed by using aircraft, satellites, Unmanned Aerial Vehicles (UAV), parachute/gliding vehicles, Roving Surface Vehicles (RSV), or Permanent Surface Installations (PSI). The various techniques proposed offer relative advantages in different scenarios. All are based on measurements of the laser energy/power incident on target surfaces of known geometric and reflective characteristics, by means of infrared detectors and/or infrared cameras calibrated for radiance. (cont.

    New techniques for laser beam atmospheric extinction measurements from manned and unmanned aerospace vehicles

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    Novel techniques for laser beam atmospheric extinction measurements, suitable for several air and space platform applications, are presented in this paper. Extinction measurements are essential to support the engineering development and the operational employment of a variety of aerospace electro-optical sensor systems, allowing calculation of the range performance attainable with such systems in current and likely future applications. Such applications include ranging, weaponry, Earth remote sensing and possible planetary exploration missions performed by satellites and unmanned flight vehicles. Unlike traditional LIDAR methods, the proposed techniques are based on measurements of the laser energy (intensity and spatial distribution) incident on target surfaces of known geometric and reflective characteristics, by means of infrared detectors and/or infrared cameras calibrated for radiance. Various laser sources can be employed with wavelengths from the visible to the far infrared portions of the spectrum, allowing for data correlation and extended sensitivity. Errors affecting measurements performed using the proposed methods are discussed in the paper and algorithms are proposed that allow a direct determination of the atmospheric transmittance and spatial characteristics of the laser spot. These algorithms take into account a variety of linear and non-linear propagation effects. Finally, results are presented relative to some experimental activities performed to validate the proposed techniques. Particularly, data are presented relative to both ground and flight trials performed with laser systems operating in the near infrared (NIR) at ?= 1064 nm and ?= 1550 nm. This includes ground tests performed with 10 Hz and 20 KHz PRF NIR laser systems in a large variety of atmospheric conditions, and flight trials performed with a 10 Hz airborne NIR laser system installed on a TORNADO aircraft, flying up to altitudes of 22,000 ft
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