Calibrations and Wind Observations of an Airborne Direct-Detection Wind LiDAR Supporting ESA’s Aeolus Mission

The Aeolus satellite mission of the European Space Agency (ESA) has brought the first wind LiDAR to space to satisfy the long-existing need for global wind profile observations. Until the successful launch on 22 August 2018, pre-launch campaign activities supported the validation of the measurement principle, the instrument calibration, and the optimization of retrieval algorithms. Therefore, an airborne prototype instrument has been developed, the ALADIN Airborne Demonstrator (A2D), with ALADIN being the Atmospheric Laser Doppler Instrument of Aeolus. Two airborne campaigns were conducted over Greenland, Iceland and the Atlantic Ocean in September 2009 and May 2015, employing the A2D as the first worldwide airborne direct-detection Doppler Wind LiDAR (DWL) and a well-established coherent 2-µm wind LiDAR. Both wind LiDAR instruments were operated on the same aircraft measuring Mie backscatter from aerosols and clouds as well as Rayleigh backscatter from molecules in parallel. This paper particularly focuses on the instrument response calibration method of the A2D and its importance for accurate wind retrieval results. We provide a detailed description of the analysis of wind measurement data gathered during the two campaigns, introducing a dedicated aerial interpolation algorithm that takes into account the different resolution grids of the two LiDAR systems. A statistical comparison of line-of-sight (LOS) winds for the campaign in 2015 yielded estimations of the systematic and random (mean absolute deviation) errors of A2D observations of about 0.7 m/s and 2.1 m/s, respectively, for the Rayleigh, and 0.05 m/s and 2.3 m/s, respectively, for the Mie channel. In view of the launch of Aeolus, differences between the A2D and the satellite mission are highlighted along the way, identifying the particular assets and drawbacks.

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The Airborne Demonstrator for the Direct-Detection Doppler Wind Lidar ALADIN on ADM-Aeolus. Part II: Simulations and Rayleigh Receiver Radiometric Performance

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2009jtecha1314.1 ◽

2009 ◽

Vol 26 (12) ◽

pp. 2516-2530 ◽

Cited By ~ 35

Author(s):

Ulrike Paffrath ◽

Christian Lemmerz ◽

Oliver Reitebuch ◽

Benjamin Witschas ◽

Ines Nikolaus ◽

...

Keyword(s):

Direct Detection ◽

European Space Agency ◽

Satellite System ◽

Satellite Mission ◽

Backscatter Signal ◽

Space Agency ◽

Expected Performance ◽

Wind Lidar ◽

Doppler Wind Lidar ◽

Signal Intensities

Abstract In the frame of the Atmospheric Dynamics Mission Aeolus (ADM-Aeolus) satellite mission by the European Space Agency (ESA), a prototype of a direct-detection Doppler wind lidar was developed to measure wind from ground and aircraft at 355 nm. Wind is measured from aerosol backscatter signal with a Fizeau interferometer and from molecular backscatter signal with a Fabry–Perot interferometer. The aim of this study is to validate the satellite instrument before launch, improve the retrieval algorithms, and consolidate the expected performance. The detected backscatter signal intensities determine the instrument wind measurement performance among other factors, such as accuracy of the calibration and stability of the optical alignment. Results of measurements and simulations for a ground-based instrument are compared, analyzed, and discussed. The simulated atmospheric aerosol models were validated by use of an additional backscatter lidar. The measured Rayleigh backscatter signals of the wind lidar prototype up to an altitude of 17 km are compared to simulations and show a good agreement by a factor better than 2, including the analyses of different error sources. First analyses of the signal at the Mie receiver from high cirrus clouds are presented. In addition, the simulations of the Rayleigh signal intensities of the Atmospheric Laser Doppler Instrument (ALADIN) Airborne Demonstrator (A2D) instrument on ground and aircraft were compared to simulations of the satellite system. The satellite signal intensities above 11.5 km are larger than those from the A2D ground-based instrument and always smaller than those from the aircraft for all altitudes.

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Retrieval of atmospheric backscatter and extinction profiles with the aladin airborne demonstrator (A2D)

EPJ Web of Conferences ◽

10.1051/epjconf/201817602021 ◽

2018 ◽

Vol 176 ◽

pp. 02021 ◽

Cited By ~ 1

Author(s):

Alexander Geiss ◽

Uwe Marksteiner ◽

Oliver Lux ◽

Christian Lemmerz ◽

Oliver Reitebuch ◽

...

Keyword(s):

Direct Detection ◽

European Space Agency ◽

Backscatter Coefficient ◽

Detection Scheme ◽

Space Agency ◽

Fabry Perot ◽

Lidar Ratio ◽

Wind Lidar ◽

Wind Retrievals ◽

Atmospheric Backscatter

By the end of 2017, the European Space Agency (ESA) will launch the Atmospheric laser Doppler instrument (ALADIN), a direct detection Doppler wind lidar operating at 355 nm. An important tool for the validation and optimization of ALADIN’s hardware and data processors for wind retrievals with real atmospheric signals is the ALADIN airborne demonstrator A2D. In order to be able to validate and test aerosol retrieval algorithms from ALADIN, an algorithm for the retrieval of atmospheric backscatter and extinction profiles from A2D is necessary. The A2D is utilizing a direct detection scheme by using a dual Fabry-Pérot interferometer to measure molecular Rayleigh signals and a Fizeau interferometer to measure aerosol Mie returns. Signals are captured by accumulation charge coupled devices (ACCD). These specifications make different steps in the signal preprocessing necessary. In this paper, the required steps to retrieve aerosol optical products, i. e. particle backscatter coefficient βp, particle extinction coefficient αp and lidar ratio Sp from A2D raw signals are described.

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First Results from the German Cal/Val Activities for Aeolus

EPJ Web of Conferences ◽

10.1051/epjconf/202023701008 ◽

2020 ◽

Vol 237 ◽

pp. 01008 ◽

Cited By ~ 1

Author(s):

Holger Baars ◽

Alexander Geiß ◽

Ulla Wandinger ◽

Alina Herzog ◽

Ronny Engelmann ◽

...

Keyword(s):

Direct Detection ◽

Weather Prediction ◽

European Space Agency ◽

High Spectral Resolution ◽

Dual Channel ◽

Space Agency ◽

First Results ◽

Global Coverage ◽

Wind Lidar ◽

Doppler Wind Lidar

On 22nd August 2018, the European Space Agency (ESA) launched the first direct detection Doppler wind lidar into space. Operating at 355 nm and acquiring signals with a dual channel receiver, it allows wind observations in clear air and particle-laden regions of the atmosphere. Furthermore, particle optical properties can be obtained using the High Spectral Resolution Technique Lidar (HSRL) technique. Measuring with 87 km horizontal and 0.25-2 km vertical resolution between ground and up to 30 km in the stratosphere, the global coverage of Aeolus observations shall fill gaps in the global observing system and thus help improving numerical weather prediction. Within this contribution, first results from the German initiative for experimental Aeolus validation are presented and discussed. Ground-based wind and aerosol measurements from tropospheric radar wind profilers, Doppler wind lidars, radiosondes, aerosol lidars and cloud radars are utilized for that purpose.

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Characterization of dark current signal measurements of the ACCDs used on-board the Aeolus satellite

10.5194/amt-2020-458 ◽

2020 ◽

Cited By ~ 1

Author(s):

Fabian Weiler ◽

Thomas Kanitz ◽

Denny Wernham ◽

Michael Rennie ◽

Dorit Huber ◽

...

Keyword(s):

Dark Current ◽

European Space Agency ◽

Current Signal ◽

Wind Retrieval ◽

Root Cause ◽

Space Agency ◽

Correction Scheme ◽

Successful Launch ◽

Wind Measurements

Abstract. Already shortly after the successful launch of the European Space Agency satellite Aeolus in August 2018, it turned out that dark current signal anomalies of single pixels (so-called hot pixels) on the Accumulation-Charge-Coupled Devices (ACCDs) of the Aeolus detectors detrimentally impact the quality of the aerosol and wind products potentially leading to wind errors of up to 4 m/s. This paper provides a detailed characterization of the hot pixels which occurred during the first one and a half years in orbit. The hot pixels are classified according to their characteristics to discuss their impact on wind measurements. Furthermore, mitigation approaches for the wind retrieval are presented and potential root causes for the hot pixel occurrence are discussed. The analysis of the dark current signal anomalies reveals a large variety of anomalies ranging from pixels with Random Telegraph Signal (RTS)-like characteristics to pixels with sporadic shifts in the median dark current signal. Moreover, the results indicate that the number of hot pixels has almost linearly increased during the observing period between 2018-09-02 until 2020-05-20 with 6 % of the ACCD pixels affected in total at the end of the period leading to 9.5 % at the end of mission lifetime. This work introduces dedicated instrument calibration modes and ground processors which allowed for a correction shortly after a hot pixel occurrence. The achieved performance with this approach avoids risky adjustments to the inflight hardware operation. It is demonstrated that the success of the correction scheme varies depending on the characteristics of each hot pixel itself. With the herein presented categorization, it is shown that multi-level RTS pixels with high fluctuation are the biggest challenge for the hot pixel correction scheme. Despite a detailed analysis in this framework, no conclusion could be drawn about the root cause of the hot pixel issue.

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Airborne direct-detection and coherent wind lidar measurements over the North Atlantic in 2015 supporting ESA’s aeolus mission

EPJ Web of Conferences ◽

10.1051/epjconf/201817602011 ◽

2018 ◽

Vol 176 ◽

pp. 02011 ◽

Cited By ~ 1

Author(s):

Uwe Marksteiner ◽

Oliver Reitebuch ◽

Christian Lemmerz ◽

Oliver Lux ◽

Stephan Rahm ◽

...

Keyword(s):

Direct Detection ◽

European Space Agency ◽

The North ◽

Space Agency ◽

Lidar Measurements ◽

Wind Measurements ◽

Measurement Principle ◽

Wind Lidar ◽

First Time ◽

Prototype Instrument

The launch of the Aeolus mission by the European Space Agency (ESA) is planned for 2018. The satellite will carry the first wind lidar in space, ALADIN (Atmospheric Laser Doppler INstrument). Its prototype instrument, the ALADIN Airborne Demonstrator (A2D), was deployed during several airborne campaigns aiming at the validation of the measurement principle and optimization of algorithms. In 2015, flights of two aircraft from DLR & NASA provided the chance to compare parallel wind measurements from four airborne wind lidars for the first time.

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Intercomparison of wind observations from ESA’s satellite mission Aeolus and the ALADIN Airborne Demonstrator

10.5194/amt-2019-431 ◽

2020 ◽

Cited By ~ 1

Author(s):

Oliver Lux ◽

Christian Lemmerz ◽

Fabian Weiler ◽

Uwe Marksteiner ◽

Benjamin Witschas ◽

...

Keyword(s):

Direct Detection ◽

European Space Agency ◽

Ultra Violet ◽

Wind Data ◽

Random Errors ◽

Satellite Mission ◽

High Coverage ◽

Wind Speeds ◽

Dual Channel ◽

Wind Lidar

Abstract. Shortly after the successful launch of ESA’s wind mission Aeolus, carried out by the European Space Agency, collocated airborne wind lidar observations were performed in Central Europe, employing the prototype of the satellite instrument, the ALADIN Airborne Demonstrator (A2D). Like the direct-detection Doppler wind lidar on-board Aeolus, the A2D is composed of a frequency-stabilised ultra-violet laser, a Cassegrain telescope and a dual-channel receiver to measure line-of-sight (LOS) wind speeds by analysing both Mie and Rayleigh backscatter signals. In the frame of the first airborne validation campaign after the launch still during the commissioning phase of the mission, four coordinated flights along the satellite swath were conducted in late autumn of 2018, yielding wind data in the troposphere with high coverage of the Rayleigh channel. Owing to the different measurement grids and viewing directions of the satellite and airborne instrument, intercomparison with the Aeolus wind product requires adequate averaging as well as conversion of the measured A2D LOS wind speeds to the satellite LOS. The statistical comparison of the two instruments with model wind data from the ECMWF shows biases of the A2D and Aeolus LOS wind speeds of −0.9 m s−1 and +1.6 m s−1, respectively, while the random errors are around 2.5 m s−1. The paper also discusses the influence of different threshold parameters implemented in the comparison algorithm as well as optimization of the A2D vertical sampling to be used in forthcoming validation campaigns.

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ALADIN Doppler Wind Lidar and Related Programs at EADS Astrium

MRS Proceedings ◽

10.1557/proc-1076-k04-02 ◽

2008 ◽

Vol 1076 ◽

Author(s):

Didier Morancais ◽

Frédéric Fabre ◽

Yves Toulemont

Keyword(s):

Direct Detection ◽

European Space Agency ◽

Doppler Lidar ◽

Wind Fields ◽

Space Agency ◽

Direct Measurements ◽

Satellite Velocity ◽

Receiver Performance ◽

Wind Lidar ◽

Flight Model

ABSTRACTThe Atmospheric Laser Doppler Instrument (ALADIN) is the payload of the ADM-AEOLUS mission, which will make direct measurements of global wind fields. It will determine the wind velocity component normal to the satellite velocity vector. The instrument is a direct detection Doppler Lidar operating in the UV, which will be the first of its kind in space.ALADIN is now in its final construction stage: the integration of the Flight Model is on-going. Most of the subsystems have been integrated; the payload performance and qualification test campaign will commence.This paper describes the ALADIN the development status and the results obtained at this stage. This regards the receiver performance, the telescope development and the challenges of the laser.The paper will also provide insights on the ATLID instrument design which is the backscatter lidar for the EarthCARE mission. This lidar program is starting its detailed design phase.The ALADIN and ATLID instruments are developed by EADS Astrium Satellites for the European Space Agency.

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Characterization of dark current signal measurements of the ACCDs used on board the Aeolus satellite

Atmospheric Measurement Techniques ◽

10.5194/amt-14-5153-2021 ◽

2021 ◽

Vol 14 (7) ◽

pp. 5153-5177

Author(s):

Fabian Weiler ◽

Thomas Kanitz ◽

Denny Wernham ◽

Michael Rennie ◽

Dorit Huber ◽

...

Keyword(s):

Dark Current ◽

European Space Agency ◽

Current Signal ◽

Wind Retrieval ◽

Root Cause ◽

Space Agency ◽

Correction Scheme ◽

Successful Launch ◽

Flight Hardware

Abstract. Even just shortly after the successful launch of the European Space Agency satellite Aeolus in August 2018, it turned out that dark current signal anomalies of single pixels (so-called “hot pixels”) on the accumulation charge-coupled devices (ACCDs) of the Aeolus detectors detrimentally impact the quality of the aerosol and wind products, potentially leading to wind errors of up to several meters per second. This paper provides a detailed characterization of the hot pixels that occurred during the first 1.5 years in orbit. The hot pixels are classified according to their characteristics to discuss their impact on wind measurements. Furthermore, mitigation approaches for the wind retrieval are presented and potential root causes for hot pixel occurrence are discussed. The analysis of the dark current signal anomalies reveals a large variety of anomalies ranging from pixels with random telegraph signal (RTS)-like characteristics to pixels with sporadic shifts in the median dark current signal. Moreover, the results indicate that the number of hot pixels almost linearly increased during the observing period between 2 September 2018 and 20 May 2020 with 6 % of the ACCD pixels affected in total at the end of the period leading to 9.5 % at the end of the mission lifetime. This work introduces dedicated instrument calibration modes and ground processors, which allowed for a correction shortly after a hot pixel occurrence. The achieved performance with this approach avoids risky adjustments to the in-flight hardware operation. It is demonstrated that the success of the correction scheme varies depending on the characteristics of each hot pixel itself. With the herein presented categorization, it is shown that multi-level RTS pixels with high fluctuation are the biggest challenge for the hot pixel correction scheme. Despite a detailed analysis in this framework, no conclusion could be drawn about the root cause of the hot pixel issue.

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OLCI A/B Tandem Phase Analysis, Part 1: Level 1 Homogenisation and Harmonisation

Remote Sensing ◽

10.3390/rs12111804 ◽

2020 ◽

Vol 12 (11) ◽

pp. 1804 ◽

Cited By ~ 6

Author(s):

Nicolas Lamquin ◽

Sébastien Clerc ◽

Ludovic Bourg ◽

Craig Donlon

Keyword(s):

European Space Agency ◽

Companion Paper ◽

The Other ◽

Satellite Mission ◽

Space Agency ◽

The Future ◽

Level 1 ◽

Level 2 ◽

Very High ◽

Sentinel 2

Copernicus is a European system for monitoring the Earth in support of European policy. It includes the Sentinel-3 satellite mission which provides reliable and up-to-date measurements of the ocean, atmosphere, cryosphere, and land. To fulfil mission requirements, two Sentinel-3 satellites are required on-orbit at the same time to meet revisit and coverage requirements in support of Copernicus Services. The inter-unit consistency is critical for the mission as more S3 platforms are planned in the future. A few weeks after its launch in April 2018, the Sentinel-3B satellite was manoeuvred into a tandem configuration with its operational twin Sentinel-3A already in orbit. Both satellites were flown only thirty seconds apart on the same orbit ground track to optimise cross-comparisons. This tandem phase lasted from early June to mid October 2018 and was followed by a short drift phase during which the Sentinel-3B satellite was progressively moved to a specific orbit phasing of 140° separation from the sentinel-3A satellite. In this paper, an output of the European Space Agency (ESA) Sentinel-3 Tandem for Climate study (S3TC), we provide a full methodology for the homogenisation and harmonisation of the two Ocean and Land Colour Instruments (OLCI) based on the tandem phase. Homogenisation adjusts for unavoidable slight spatial and spectral differences between the two sensors and provide a basis for the comparison of the radiometry. Persistent radiometric biases of 1–2% across the OLCI spectrum are found with very high confidence. Harmonisation then consists of adjusting one instrument on the other based on these findings. Validation of the approach shows that such harmonisation then procures an excellent radiometric alignment. Performed on L1 calibrated radiances, the benefits of harmonisation are fully appreciated on Level 2 products as reported in a companion paper. Whereas our methodology aligns one sensor to behave radiometrically as the other, discussions consider the choice of the reference to be used within the operational framework. Further exploitation of the measurements indeed provides evidence of the need to perform flat-fielding on both payloads, prior to any harmonisation. Such flat-fielding notably removes inter-camera differences in the harmonisation coefficients. We conclude on the extreme usefulness of performing a tandem phase for the OLCI mission continuity as well as for any optical mission to which the methodology presented in this paper applies (e.g., Sentinel-2). To maintain the climate record, it is highly recommended that the future Sentinel-3C and Sentinel-3D satellites perform tandem flights when injected into the Sentinel-3 time series.

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Development of Embedded Boot Software for a Satellite Instrument Control Unit: Lessons Learned

International Journal of Aerospace Engineering ◽

10.1155/2019/8625378 ◽

2019 ◽

Vol 2019 ◽

pp. 1-8

Author(s):

Jesús Fernández-Conde ◽

Jaime Gómez-Saez-de-Tejada ◽

David Pérez-Lizán ◽

Rafael Toledo-Moreo

Keyword(s):

Real Time ◽

European Space Agency ◽

Control Unit ◽

Lessons Learned ◽

System Failure ◽

Application Software ◽

Satellite Mission ◽

Space Agency ◽

Expected Performance ◽

Instrument Control

A satellite spacecraft is generally composed of a central Control and Data Management Unit (CDMU) and several instruments, each one locally controlled by its Instrument Control Unit (ICU). Inside each ICU, the embedded boot software (BSW) is the very first piece of software executed after power-up or reset. The ICU BSW is a nonpatchable, stand-alone, real-time software package that initializes the ICU HW, performs self-tests, and waits for CDMU commands to maintain on-board memory and ultimately start a patchable application software (ASW), which is responsible for execution of the nominal tasks assigned to the ICU (control of the satellite instrument being the most important one). The BSW is a relatively small but critical software item, since an unexpected behaviour can cause or contribute to a system failure resulting in fatal consequences such as the satellite mission loss. The development of this kind of embedded software is special in many senses, primarily due to its criticality, real-time expected performance, and the constrained size of program and data memories. This paper presents the lessons learned in the development and HW/SW integration phases of a satellite ICU BSW designed for a European Space Agency mission.

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