DEMONSTRATED AEOLUS BENEFITS IN ATMOSPHERIC SCIENCES

International audienceWe highlight some of the scientific benefits of the Aeolus Doppler Wind Lidar mission since its launch in August 2018. Its scientific objectives are to improve weather forecasts and to advance the understanding of atmospheric dynamics and its interaction with the atmospheric energy and water cycle. A number of meteorological and science institutes across the world are starting to demonstrate that the Aeolus mission objectives are being met. Its wind product is being operationally assimilated by four Numerical Weather Prediction (NWP) centres, thanks to demonstrated useful positive impact on NWP analyses and forecasts. Applications of its atmospheric optical properties product have been found, e.g., in the detection and tracking of smoke from the extreme Australian wildfires of 2020 and in atmospheric composition data assimilation. The winds are finding novel applications in atmospheric dynamics research, such as tropical phenomena (Quasi-Biennial Oscillation disruption events), detection of atmospheric gravity waves, and in the smoke generated vortex associated with the Australian wildfires. It has been applied in the assessment of other types of satellite derived wind information such as atmospheric motions vectors. Aeolus is already successful with hopefully more to come

ESA's Space-based Doppler Wind Lidar Mission Aeolus - First Wind and Aerosol Product Assessment Results

The European Space Agency (ESA) wind mission, Aeolus, hosts the first space-based Doppler Wind Lidar (DWL) world-wide. The primary mission objective is to demonstrate the DWL technique for measuring wind profiles from space, intended for assimilation in Numerical Weather Prediction (NWP) models. The wind observations will also be used to advance atmospheric dynamics research and for evaluation of climate models. Mission spinoff products are profiles of cloud and aerosol optical properties. Aeolus was launched on 22 August 2018, and the Atmospheric LAser Doppler INstrument (Aladin) instrument switch-on was completed with first high energy output in wind mode on 4 September 2018. The on-ground data processing facility worked excellent, allowing L2 product output in near-real-time from the start of the mission. First results from the wind profile product (L2B) assessment show that the winds are of very high quality, with random errors in the free Troposphere within (cloud/aerosol backscatter winds: 2.1 m/s) and larger (molecular backscatter winds: 4.3 m/s) than the requirements (2.5 m/s), but still allowing significant positive impact in first preliminary NWP impact experiments. The higher than expected random errors at the time of writing are amongst others due to a lower instrument outand input photon budget than designed. The instrument calibration is working well, and some of the data processing steps are currently being refined to allow to fully correct instrument alignment related drifts and elevated detector dark currents causing biases in the first data product version. The optical properties spin-off product (L2A) is being compared e.g. to NWP model clouds, air quality model forecasts, and collocated ground-based observations. Features including optically thick and thin particle and hydrometeor layers are clearly identified and are being validated

Data quality of Aeolus wind measurements

The European Space Agency (ESA)'s Earth Explorer Aeolus was launched in August 2018 carrying the world's first spaceborne wind lidar, the Atmospheric Laser Doppler Instrument (ALADIN). ALADIN uses a high spectral resolution Doppler wind lidar operating at 355nm to measure profiles of line-of-sight wind components in near-real-time (NRT). ALADIN samples the atmosphere from 30km altitude down to the Earth's surface or to the level where the lidar signal is attenuated by optically thick clouds. The global wind profiles provided by ALADIN help to improve weather forecasting and the understanding of atmospheric dynamics as they fill observational gaps in vertically resolved wind profiles mainly in the tropics, southern hemisphere, and over the northern hemisphere oceans. In January 2020, the European Centre for Medium-Range Weather Forecasts (ECMWF) became the first numerical weather prediction (NWP) centre to assimilate Aeolus observations for operational forecasting. A main prerequisite for beneficial impact is data of sufficient quality. Such high data quality has been achieved through close collaboration of all involved parties within the Aeolus Data Innovation and Science Cluster (DISC), which was established after launch to study and improve the data quality of Aeolus products. The tasks of the Aeolus DISC include the instrument and platform monitoring, calibration, characterization, retrieval algorithm refinement, processor evolution, quality monitoring, product validation, and impact assessment for NWP. The achievements of the Aeolus DISC for the NRT data quality and the current status of Aeolus wind measurements will be described and summarized. Further, an outlook on future improvements and the availability of reprocessed datasets with enhanced data quality will be provided

HETEAC: The Aerosol Classification Model for EarthCARE

We introduce the Hybrid End-To-End Aerosol Classification (HETEAC) model for the upcoming EarthCARE mission. The model serves as the common baseline for development, evaluation, and implementation of EarthCARE algorithms. It shall ensure the consistency of different aerosol products from the multi-instrument platform as well as facilitate the conform specification of broad-band optical properties necessary for the EarthCARE radiative closure efforts. The hybrid approach ensures the theoretical description of aerosol microphysics consistent with the optical properties of various aerosol types known from observations. The end-to-end model permits the uniform representation of aerosol types in terms of microphysical, optical and radiative properties

Initial Assessment of the Performance of the First Wind Lidar in Space on Aeolus

Soon after its successful launch in August 2018, the spaceborne wind lidar ALADIN (Atmospheric LAser Doppler INstrument) on-board ESA's Earth Explorer satellite Aeolus has demonstrated to provide atmospheric wind profiles on a global scale. Being the first ever Doppler Wind Lidar (DWL) instrument in space, ALADIN contributes to the improvement in numerical weather prediction (NWP) by measuring one component of the horizontal wind vector. The performance of the ALADIN instrument was assessed by a team from ESA, DLR, industry, and NWP centers during the first months of operation. The current knowledge about the main contributors to the random and systematic errors from the instrument will be discussed. First validation results from an airborne campaign with two wind lidars on-board the DLR Falcon aircraft will be shown

Data quality of Aeolus wind measurements

The European Space Agency (ESA)'s Earth Explorer Aeolus was launched in August 2018 carrying the world's first spaceborne wind lidar, the Atmospheric Laser Doppler Instrument (ALADIN). ALADIN uses a high spectral resolution Doppler wind lidar operating at 355nm to determine profiles of line-of-sight wind components in near-real-time (NRT). ALADIN samples the atmosphere from 30km altitude down to the Earth's surface or to the level where the lidar signal is attenuated by optically thick clouds. The global wind profiles provided by ALADIN help to improve weather forecasting and the understanding of atmospheric dynamics as they fill observational gaps in vertically resolved wind profiles mainly in the tropics, southern hemisphere, and over the northern hemisphere oceans. Since 2020, multiple national and international weather centres (e.g. ECMWF, DWD, Météo France, MetOffice) assimilate Aeolus observations in their operational forecasting. Additionally, the scientific exploitation of the Aeolus dataset has started. A main prerequisite for beneficial impact and scientific exploitation is data of sufficient quality. Such high data quality has been achieved through close collaboration of all involved parties within the Aeolus Data Innovation and Science Cluster (DISC), which was established after launch to study and improve the data quality of Aeolus products. The tasks of the Aeolus DISC include the instrument and platform monitoring, calibration, characterization, retrieval algorithm refinement, processor evolution, quality monitoring, product validation, and impact assessment for NWP. The achievements of the Aeolus DISC for the NRT data quality and the one currently available reprocessed dataset will be presented. The data quality of the Aeolus wind measurements will be described and an outlook on planned improvements of the dataset and processors will be provided

The Aeolus Data Innovation and Science Cluster

The Data Innovation and Science Cluster (DISC) is a core element of ESA's data quality strategy for the Aeolus mission, which was launched in August 2018. Aeolus provides for the first-time global observations of vertical profiles of horizontal wind information by using the first Doppler wind lidar in space. The Aeolus DISC is responsible for monitoring and improving the quality of the Aeolus aerosol and wind products, for the upgrade of the operational processors as well as for impact studies and support of data usage. It has been responsible for multiple significant processor upgrades which reduced the systematic error of the Aeolus observations drastically. Only due to the efforts of the Aeolus DISC team members prior to and after launch, the systematic error of the Aeolus wind products could be reduced to a global average below 1 m/s which was an important pre-requisite for making the data available to the public in May 2020 and for its use in operational weather prediction. In 2020, the reprocessing of earlier acquired Aeolus data, another important task of the Aeolus DISC, also started. In this way, also observations from June to December 2019 with significantly better quality could be made available to the public, and more data will follow this and next year. Without the thorough preparations and close collaboration between ESA and the Aeolus DISC over the past decade, many of these achievements would not have been possible

Contributions from the DISC to accomplish the Aeolus mission objectives

The Aeolus Data Innovation and Science Cluster (DISC) supports the Aeolus mission with a wide range of activities from instrument and product quality monitoring over retrieval algorithm improvements to numerical weather prediction (NWP) impact assessments for wind and aerosols. The Aeolus DISC provides support to ESA, Cal/Val teams, numerical weather prediction (NWP) centers, and scientific users for instrument special operations and calibration, for the re-processing of Aeolus products from the past and through the provision of bi-annual updates of the L1A, L1B, L2A and L2B operational processors. The Aeolus DISC is coordinated by DLR with partners from ECMWF, KNMI, Météo-France, TROPOS, DoRIT, ABB, s&t, serco, OLA, Physics Solutions, IB Reissig and Les Myriades involving more than 40 scientists and engineers. The presentation will highlight the Aeolus DISC activities with a focus for the year 2021 and early 2022 since the last Aeolus workshop in November 2020. This covers the evolution of the instrument performance including investigations of the cause of the on-going signal loss and the achieved improvement via dedicated laser tests in 2021. In addition, refinements of algorithms and correction of the wind bias will be discussed - including a known remaining seasonal bias in October and March as encountered during the re-processing campaigns. Finally, the strategy for the on-going and future re-processing campaigns will be addressed to inform the scientific community about the availability and quality of the re-processed data products. The Aeolus mission has fully achieved its mission objectives including the unprecedented demonstration of direct-detection Doppler wind lidar technology and high-power laser operation in space in the ultraviolet spectral region over its planned full mission lifetime of 3 years and 3 months. Aeolus wind products have clearly demonstrated positive impact on forecasts using several NWP models. Since early 2020, and thus only 1.5 years after launch, the Aeolus wind products are used in operation at various NWP centers worldwide. This was achieved even despite the larger than expected wind random errors due to lower initial atmospheric signal levels and the observed signal losses during the operation of the first and second laser. In addition to this incredible success, first scientific studies demonstrated the use of Aeolus for atmospheric dynamics research in the stratosphere and for the analysis of aerosol transport. These achievements of the Aeolus mission and its success were only possible with the essential and critical contributions from the Aeolus DISC. This demonstrates the need and potential for setting up such scientific consortia covering a wide range of expertise from instrument, processors, and scientific use of products for Earth Explorer type missions. The invaluable experience gained by the Aeolus DISC during the more then 3 years of Aeolus mission in orbit (preceded by a period of 20 years before launch by a similar study team) is a pre-requisite for a successful preparation of an operational follow-on Aeolus-2 mission

Quantitative Integration in ein numerisches Strahlungstransportmodell des Atmosphäre-Ozean Systems und Analyse des Einflusses auf Fernerkundungsanwendungen

The inelastic (Raman) scattering of daylight due to due vibrational state transitions of liquid water is known to have a significant influence on the spectra of ocean leaving radiation. This effect therefore needs to be considered in radiative transfer (RT) models of the atmosphere-ocean system for which a high accuracy is required, e.g. for ocean color remote sensing applications. While many qualitative studies of the effect have been published in the past decades, a lack of fast radiative transfer models of the combined atmosphere-ocean system that allow for a detailed angular and spectral investigation of the effect had been identified. In this thesis, a method for the quantitative and angular resolved incorporation of water Raman scattering effects into a matrix-operator radiative transfer model of the coupled atmosphere-ocean system has been developed, implemented, validated, and applied to several problems. The theoretical and empirical basis for the optical properties of Raman scattering, including the spectral redistribution, the phase function, and the scattering coefficient, are discussed, as they are important input values for a radiative transfer model. Furthermore, the optical properties of two other inelastic scattering effects are discussed: the rotational Raman scattering of atmospheric nitrogen and oxygen, and the fluorescence of yellow substance and chlorophyll in the ocean. An approach focused on accuracy and computation speed was developed for the incorporation of water Raman scattering into an existing radiative transfer model based on the matrix-operator method. Furthermore, the new model was accompanied by preprocessors for the salinity and temperature dependent computation of elastic scattering and absorption-coefficients of water, as well as for the optical properties of dissolved and suspended oceanic matter. The new RT model version was then successfully validated by a comparison of the results for canonical problems to those of other radiative transfer models. To validate components of the model that were not featured by the other models, e.g. the precise angular dependence of the Raman contribution, sanity and consistency checks of contributing model components were performed. Applications performed with the new model include a detailed study of the Raman contribution to radiation emerging from Case 1 waters, which reaches several tens of percent in the visible spectral range for clear water. The reduction of the effect in turbid waters and the effect of the water salinity was also studied. Angular effects have proven to be significant, whereas higher orders of Raman scattering are shown to be of minor importance. The Raman contribution was also studied at the top of the atmosphere, and it was shown that the Raman scattered radiation fraction for a standard case will be detectable in all visible channels of the upcoming OLCI instrument on the ESA Sentinel-3 Satellite. Finally, the new RT model version was used in an ocean constituent retrieval scheme, which is adaptable to the spectral channels of different remote sensing satellites.Die inelastische Raman Streuung von Licht an Vibrationszustandsübergängen des flüssigen Wassers hat einen starken Einfluss auf das Spektrum des kurzwelligen Lichtes welches mit dem Ozean in Wechselwirkung steht. Hieraus ergibt sich die Notwendigkeit, diesen Effekt für eine akkurate Beschreibung des Strahlungstransports im Ozean und der Atmosphäre zu berücksichtigen. Dies trifft insbesondere auf Strahlungstransport Simulationen für den Anwendungsbereich der Ozeanfernerkundung zu, kann aber aufgrund der Größenordnung des Effekts auch eine Rolle bei der Atmosphärenfernerkundung über dem Ozean spielen. Während einige bestehende Strahlungstransportmodelle den Effekt qualitativ berücksichtigen, bestand jedoch ein Mangel an Modellen welche den Einfluss des Effekts auf das gekoppelte Atmosphäre-Ozean System unter Berücksichtigung der azimutalen Winkelabhängigkeit vorhersagen können. In der vorliegenden Arbeit wurde daher ein Verfahren zur Berücksichtigung der inelastischen Raman Streuung an Vibrationsübergängen des flüssigen Wassers in einem numerischen Strahlungstransportmodell entwickelt, implementiert, validiert und angewendet. Zunächst werden hierzu die theoretischen und empirischen Grundlagen beschrieben, die zur genauen Berechnung des Effekts notwendig sind. Ferner wurden ebenfalls die Grundlagen weiterer inelastischer Streuprozesse, insbesondere der atmosphärischen Raman Streuung aber auch der Fluoreszenz von Ozeaninhaltsstoffen, zusammengetragen und für ersteres in Form von Vorprozessoren für die künftige Verwendung im Strahlungstransportmodell vorbereitet. In dem folgenden Abschnitt wird das Strahlungstransportmodell, mit Schwerpunkt auf den neu entwickelten Verfahren zur Einbindung der inelastischen Streuung, erläutert. Dies beinhaltet die Berechnung der Streueffekte mit Fourier-entwickelter Azimutalabhängigkeit und eine akkurate aber dennoch schnelle Methode zur Berechnung der Raman Streubeiträge in optisch dicken, homogenen Schichten. Ferner wurden einige Erweiterungen an dem Modell bezüglich der Berechnung von Streu- und Absorptionseigenschaften des Wassers in Abhängigkeit von Temperatur und Salinität vorgenommen. Ebenfalls werden die in der Arbeit Verwendung findenden bio-optischen Modelle beschrieben. Ein weiterer Abschnitt befasst sich mit der Validierung der neuen Modellversion. Dies stellte aufgrund des Mangels an zur Verfügung stehenden geeigneten Referenzmodellen, die ebenfalls die Winkelabhängigkeit der Raman Streuung korrekt berücksichtigen, eine Herausforderung dar. Daher wurde ein gemischter Ansatz gewählt, der aus Modellvergleichen für einfache kanonische Probleme, der Überprüfung der Konsistenz der beteiligten Berechnungen sowie dem qualitativen Vergleich der Winkelabhängigkeit mit erwarteten Verläufen bestand. Der letzte Abschnitt stellt einige Anwendungen des neuen Modells vor. Hervorzuheben ist eine umfangreiche Studie des Einflusses der Raman Streuung auf die Lichtfelder in Ozean und Atmosphäre im sichtbaren Spektralbereich. So beträgt der Anteil des zusätzlich erzeugten Lichtes gegenüber der Vernachlässigung des Effekts im aufwärtsgerichteten Strahlungsfeld an der Ozeanoberfläche in klaren Gewässern von 10 bis über 30%. Es stellte sich heraus dass eine Vernachlässigung der Winkelabhängigkeit des Effekts zu Fehlern in den Radianzen von mehreren Prozent führen kann. Da der Anteil des aus dem Ozean entwichenen Lichtes am Oberrand der Atmosphäre im sichtbaren Strahlungsbereich in grober Schätzung nur noch etwa 10% beträgt, wurde auch untersucht wie stark der Effekt die Signale am Oberrand der Atmosphäre beeinflusst, um Rückschlüsse auf Satelliten-Fernerkundungsverfahren zu ermöglichen. Auch hier können die Raman Beiträge etliche Prozent betragen. Dies ist hauptsächlich im blauen und grünen Spektralbereich der Fall und weniger im roten, wo der Ozean stark absorbiert. Es wird auch gezeigt, dass selbst in dem Winkelbereich über einem durch Wind aufgerauten Ozean, der durch direkte Sonnenreflexe beeinflusst ist, der Beitrag noch durchaus signifikant sein kann. Eine weitere Studie beschäftigt sich spezifisch mit dem Effekt in den Kanälen des künftigen abbildenden Spektrometers OLCI der ESA Sentinel-3 Mission. Hierbei konnte u.A. gezeigt werden, dass der Raman Beitrag selbst in den roten Spektralkanälen noch technisch von dem Instrument aufgelöst werden kann. Der abschließende Beitrag stellt ein Gemeinschaftsprojekt unseres Instituts mit der Firma Brockmann Consult vor, in der die neue Strahlungstransportmodellversion erfolgreich zur Erstellung einer Lookup- Tabelle für ein allgemeines Fernerkundungsverfahren für Inhaltsstoffe des Ozeans zur Verwendung kam

DEMONSTRATED AEOLUS BENEFITS IN ATMOSPHERIC SCIENCES

We highlight some of the scientific benefits of the Aeolus Doppler Wind Lidar mission since its launch in August 2018. Its scientific objectives are to improve weather forecasts and to advance the understanding of atmospheric dynamics and its interaction with the atmospheric energy and water cycle. A number of meteorological and science institutes across the world are starting to demonstrate that the Aeolus mission objectives are being met. Its wind product is being operationally assimilated by four Numerical Weather Prediction (NWP) centres, thanks to demonstrated useful positive impact on NWP analyses and forecasts. Applications of its atmospheric optical properties product have been found, e.g., in the detection and tracking of smoke from the extreme Australian wildfires of 2020 and in atmospheric composition data assimilation. The winds are finding novel applications in atmospheric dynamics research, such as tropical phenomena (Quasi-Biennial Oscillation disruption events), detection of atmospheric gravity waves, and in the smoke generated vortex associated with the Australian wildfires. It has been applied in the assessment of other types of satellite derived wind information such as atmospheric motions vectors. Aeolus is already successful with hopefully more to come.</p