Results from recent airborne campaigns aiming at the preparation of ESA’s Aeolus Wind Lidar Mission CLRC 2018 – 19th Coherent Laser Radar Conference 18th to 21st June, 2018, Okinawa, Japan Benjamin Witschas, Christian Lemmerz, Oliver Lux, Uwe Marksteiner, Stephan Rahm, Oliver Reitebuch, Andreas Schäfler, Fabian Weiler I want to thank the conference committee for the invitation and the great organization of the conference And acknowledge my co-authors that contributed to the results presented in this talk which is about the cal/val activities of Aeolus at DLR

August 21st, 21:20 UTC And this slight shows the reason why the talk is more important than ever before We already heard that the Aeolus development took about 20 years, and right at this moment, the instrument is on the ship on its way to Kourou – the Launch site It is not surprising that a satellite carrying such a breakthrough technology needs calibration and validation of the measurement principle, algorithms and measurement strategies. Such support is provided by DLR for almost 15 years. In this talk (überblenden auf nächste folie): Overview of the CalVal payload by DLR Results from the recent Nawdex campaign CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

The DLR airborne payload for Aeolus Cal/Val Outline The DLR airborne payload for Aeolus Cal/Val Results from the NAWDEX campaign 2016 Summary and overview of planned Aeolus Cal/Val activities at DLR CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

The DLR airborne payload for Aeolus Cal/Val A coherent and a direct detection Doppler wind lidar on-board DLR’s Falcon 2-µm DWL power supply and cooling unit Temperature stabilized A2D receiver 2-µm DWL transceiver 2-µm DWL data acquisition unit A2D data acquisition unit, power supply and cooling unit are mounted on two racks in the back (not visible) A2D laser A2D telescope Picture of the CalVal payload integrated in the DLR Falcon aircraft 2µm coherent A2D direct detection Aircraft fully packed, only space for two operators and no toilet on board! CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

The DLR airborne payload for Aeolus Cal/Val Specifications Demonstrator Reference Parameter DLR A2D [1] DLR 2-µm DWL [2] Detection principle Direct detection Coherent detection Scanning Fixed line-of-sight Double-wedge scanner Wavelength 354.89 nm 2022.54 nm Laser energy 50-60 mJ 1-2 mJ Pulse repetition rate 50 Hz 500 Hz Pulse length 20 ns (FWHM) 400-500 ns (FWHM) Telescope diameter 20 cm 10.8 cm Vertical resolution 300 m to 2.4 km 100 m Temporal averaging raw data (horizontal) 20 shots = 400 ms single shot = 2 ms Temporal averaging product (horizontal) 14 s (+4 s data gap) 1 s per LOS (500 shots), 42 s scan (21 LOS) Horizontal resolution 3.6 km (18 s) 0.2 km LOS, 8.4 km scan Precision (random error) 1.5 m/s (Mie) 2.5 m/s (Rayleigh) < 1 m/s Parameter DLR Falcon Max. Range 3700 km Max. Altitude 12800 m Max. Endurance 4-5 h (dep. on altitude) Take-off distance 2000 m Pressurized Cabin Yes Long Range Speed 245 m/s Most important differences: Demonstrator vs reference Direct vs coherent Fixed LOS vs scanning Resolutions Precision; from the precision value it already gets clear why the 2-µm is the reference system for the calibration activities, whereas the precision for the wind speed measurements is mainly determined by comparison to dropsonde measurements (übergang zu nächster Folie) [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. [2] Witschas et al., 2017, Journal of Atmospheric and Oceanic Technology 34. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

DLR 2µm – Coherent Doppler Wind Lidar The reference instrument for Aeolus Cal/Val activities at DLR Wind vector is available as the system is equipped with a double wedge scanner „No“ systematic bias due to coherent detection and possible flight attitude correction by ground returns The accuracy of 2-µm DWL winds was proven by means of several airborne campaigns data, e.g., by comparison to Dropsonde wind data: Bias: 0.00 m/s; STD*: 1.20 m/s [1] – hor. wind Bias: 0.08 m/s; STD*: 0.92 m/s [2] – hor. wind Bias: 0.05 m/s, STD*: 0.20 m/s [3] – vert. wind Bias: 0.10 m/s, STD*: 1.30 m/s [4] – hor. wind (from NAWDEX – comparison to HALO dropsondes) * STD considers the uncertainty of dropsonde and lidar measurements Only read the for bias values and STDs and conclude that the retrieved wind speed is quasi bias free and with a standard deviation of 1 m/s. [1] Weissmann et al., 2005, Journal of Atmospheric and Oceanic Technology, Vol. 22. [2] Chouza et al., 2016, Atmospheric Chemistry and Physics, Vol. 16. [3] Witschas et al., 2017, Journal of Atmospheric and Oceanic Technology Vol. 34. [4] DLR, 2018, WindVal II, final report, Wind validation II for Aeolus. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

DLR direct detection Doppler Wind Lidar – A2D The ALADIN (Aeolus) airborne demonstrator for Cal/Val activities at DLR Similar receiver and laser as the satellite instrument Similar measurement geometry (fixed LOS); 20° off-nadir instead of 37.5° off-nadir PRF = 50 Hz E = 60 mJ τ = 20 ns δf = 5 MHz On this slight, the totally different receiver architecture of the A2D is shown: Shortly explain Mie and Rayleigh channel and the beauty of getting wind from molecular return For those who are not familiar with double edge, shortly explain or refer to the talk by Alain [1] Reitebuch et al., 2009, Journal of Atmospheric and Oceanic Technology, Vol. 26. [2] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. [3] Lemmerz et al., 2017, Applied Optics, Vol. 56. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

2-µm DWL (the reference): Coherent detection with scanner The airborne Aeolus Cal/Val payload by DLR Comparison of the two Doppler Wind Lidars on-board the DLR Falcon 2-µm DWL (the reference): Coherent detection with scanner Bias free wind speed (and direction) measurements Coverage depending on aerosol load A2D (the demonstrator): Direct detection without scanner (only fixed LOS) Same configuration as ALADIN Wind speed from particulate and molecular returns Calibration needed for wind retrieval – possible error source So we have to different wind lidars on board, where the 2-µm is a coherent detection, bias free wind lidar that deliver wind speed and direction…..however, it is restricted to aerosol backscatter which can be a real limitation in very clean regions as the arctic or e.g. New Zealand On the other hand we have the A2D which has a similar setup as the Aeolus instrument and which yields wind from particulate and molecular backscatter….however, due to the direct detection, the A2D needs to be calibrated which is an additional error source… CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

An overview of airborne wind lidar activities by DLR 10/2009, Keflavik, Iceland 2007/2008, DLR, Germany A-TReC 2003 ADM 2009 WindVAL 2015 WindVal II/NAWDEX 2016 GW-LCYCLE I/II 2013/2016 ADM 2007/08 05/2015, Keflavik, Iceland Eyjafjalla- jökull 2010 A-LIFE 2017 MAP 1999 ESCOMPTE 2001 VERTIKATOR 2002 COPS 2007 T-PARC 2008 Aeolus / NWP 09/10/2016, Keflavik, Iceland SALTRACE 2013 AMMA 2006 mesoscale gravity waves aerosol - This slight gives an overview of airborne field campaigns with Doppler Wind Lidars by DLR, demonstrating the long lasting experience whereas you can see that the DWL are used in order to study different scientific issues as mesoscale xxx, gravity wave, aerosol optical properties and atmospheric dynamics. The campaigns related to Aeolus and performed with the just explained payload are marked in blue. You can see that a young team started in 2007, …….getting older, but still are motivated and enthusiastic,….and getting support (NASA DC8) and Halo/Safire… Resulting in 150 recommendations to ESA Italic = 10-µm DWL - WIND Underlined = 2-µm DWL Normal = A2D and 2-µm DWL DEEPWAVE 2014 CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

The DLR airborne payload for Aeolus Cal/Val Outline The DLR airborne payload for Aeolus Cal/Val Results from the NAWDEX campaign 2016 In the following I want to show wind measurements from the recent NAWDEX campaign performed in 2016 out of Iceland Summary and overview of planned Aeolus Cal/Val activities at DLR CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

North Atlantic Waveguide and Downstream Impact Experiment - NAWDEX September – October 2016, Keflavik, Iceland Overarching scientific hypothesis [1]: Diabatic processes over the North Atlantic have a major influence on jet stream meanders, the downstream development of Rossby waves on the tropopause and high impact weather over Europe. HALO: 4λ-H20+HSRL, 35.2 GHz Doppler radar, microwave radiometer, spectral radiometer, imaging spectrometer, dropsondes DLR Falcon: 2-µm coherent detection and A2D direct detection Doppler Wind Lidar SAFIRE Falcon: 355 nm HSRL, 95 GHz Doppler radar, dropsondes - The overarching goal of NAWDEX was to investigate the impact of diabatic processes over the North Atlantic on the jet stream meanders, the downstream development of Rossby waves on the Tropopause and on high impact weather over Europe In order to reach this goal a bunch of institutes and organizations and aircraft came to Iceland in Sep/Oct 2016, as the Halo aircraft equipped with, the DLR Falcon with the CalVal payload and the French Falcon  2 times EarthCare payload, 1 Time Aeolus payload… Thus, NAWDEX …READ LAST SENTENCE FROM SLIGHT Multi-aircraft field campaign, with Aeolus/EarthCARE payloads enabling further verification of measurement strategies under complex meteorological scenes for future CalVal campaigns [1] Schäfler et al., 2017, Bull. Amer. Meteor. Soc., (accepted) https://doi.org/10.1175/BAMS-D-17-0003.1. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

2-µm DWL measurements during NAWDEX An overview DLR Falcon flight tracks during NAWDEX 12 research flights during the campaign + 2 additional calibration flights + 2 aerosol flights over Southern Europe 50 h flight hours (15 h of A2D wind measurements) 12 flights, 50 flight hours and almost the same amount of 2-µm wind measurements… Flights to Greenland, Scotland, and around Iceland 2-µm can measure still during ascent, about 10 minutes after take-off Most of the flights were related to the investigation of the jet-stream (high wind speeds, strong gradients)  good for validation [1] Schäfler et al., 2017, Bull. Amer. Meteor. Soc., (accepted) https://doi.org/10.1175/BAMS-D-17-0003.1. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

2-µm DWL data and A2D data are interpolated to the same grid Statistical comparison of 2-µm DWL and A2D DWL measurements 4 October 2016 – Jet stream crossing 2-µm DWL measurement For comparison: 2-µm DWL data and A2D data are interpolated to the same grid 2-µm DWL data is projected onto the line-of-sight direction of the A2D [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

Statistical comparison of 2-µm DWL and A2D DWL measurements 4 October 2016 – Jet stream crossing A2D winds from Mie-channel (particles) and Rayleigh- channel (molecules). [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

Statistical comparison of 2-µm DWL and A2D DWL measurements 4 October 2016 – Jet stream crossing [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

2-µm DWL data and A2D data are interpolated to the same grid Statistical comparison of 2-µm DWL and A2D DWL measurements 27 September 2016 – Jet stream crossing 2-µm DWL measurement 2-µm DWL measurement For comparison 2-µm DWL data and A2D data are interpolated to the same grid 2-µm DWL data is projected onto the line-of-sight direction of the A2D [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

Statistical comparison of 2-µm DWL and A2D DWL measurements 27 September 2016 – Jet stream crossing A2D winds from Mie-channel (particles) and Rayleigh- channel (molecules). [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

Statistical comparison of 2-µm DWL and A2D DWL measurements 27 September 2016 – Jet stream crossing [1] Lux et al., 2018, Atmospheric Measurement Techniques, 11, 3297 – 3322. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

The DLR airborne payload for Aeolus Cal/Val Outline The DLR airborne payload for Aeolus Cal/Val Results from the NAWDEX campaign 2016 Summary and overview of planned Aeolus Cal/Val activities at DLR CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

Fig. credits ESA Summary DLR has developed an airborne AEOLUS calibration and validation payload which has been operated in several field campaigns within the last 10 years It is demonstrated that it is very useful to fly the combination of a coherent detection and a direct detection DWL Verification of the A2D/ALADIN principle and accuracy by means of 2-µm DWL measurements Remarkable extension of the coverage of wind measurements by the A2D Rayleigh channel DLR provided more than 150 recommendations about Aeolus operation, calibration and retrieval algorithms to ESA Based on previous field campaigns data, DLR has optimized strategies for upcoming Cal/Val activities After satellite launch, DLR will lead the Data, Innovation and Science Cluster (DISC) to coordinate the exploitation of the Aeolus mission by expert teams including ECMWF, Météo-France and KNMI. CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas

Outlook Airborne campaigns for Aeolus validation at DLR Fig. credits ESA Outlook Airborne campaigns for Aeolus validation at DLR Post-Launch Rehearsal campaign Nov 2018 Central Europe, (DLR) Post-Launch Calibration campaign April/May 2019 Central Europe, (DLR) Tropical Validation campaign Q1 2020 TBD 2018 2019 2020 2021 Aeolus Launch 21. August 2018 21:20 UTC Artic Calibration campaign September 2019 Keflavik, Iceland Artic Calibration campaign 2021 TBD Data innovation and Science Cluster - DISC http://earth.esa.int/aos/AeolusCalVal CLRC 2018 – 19th Coherent Laser Radar Conference – B. Witschas