Results from the ADM-Aeolus Pre-Launch Ground and Airborne Campaigns in 2007

Transcription

1 Results from the ADM-Aeolus Pre-Launch Ground and Airborne Campaigns in 2007 O. Reitebuch 1, M. Endemann 2, C. Lemmerz 1, U. Paffrath 1, B. Witschas 1, V. Freudenthaler 3, V. Lehmann 4, D. Engelbart 4 1 DLR Oberpaffenhofen, 2 ESA-ESTEC Noordwijk, 3 University Munich, 4 DWD Lindenberg Institut für Physik der Atmosphäre

2 First ground campaign in October 2006 Second ground campaign in July 2007 ADM-Aeolus Pre-Launch Ground Campaigns Objectives: Validate ALADIN instrument before launch with atmospheric signal and derive conclusions for retrieval algorithms and for on-ground and in-orbit test, verification and calibration of satellite instrument Specific topics are: radiometric and wind measurement performance, calibration procedures for Mie and Rayleigh spectrometers, quality-control, Rayleigh wind correction schemes (T, p), ground detection and zero-wind calibration Site: Meteorological Observatory of DWD in Lindenberg (southeast of Berlin, Northeast Germany); flat terrain Campaign Team: 20 participants from DWD, University Munich, and DLR =>

3 Instruments at DWD Lindenberg for Ground Campaigns Windprofiler site ALADIN Airborne Demonstrator A2D (LOS winds) 355 nm DLR 2-µm Doppler Lidar (wind up to 2-3 km); only Oct. 06 University Munich aerosol lidar MULIS (backscatter, extinction coefficient up to 10 km) 355 nm, 532 nm, Raman 482 MHz windprofiler with RASS (wind up to 16 km, temperature up to 4 km) 1290 MHz windprofiler (wind up to 1.5 km) ceilometer (clouds up to 12 km, aerosol backscatter in boundary layer) Optic laboratory (distance 500 m) 355 nm Raman-lidar RAMSES (profiles of water vapour mixing ratio and backscatter ratio during night) sun photometer (aerosol optical depth during day) 35.5 GHz cloud radar (reflectivity, vertical velocity, linear depolarisation ratio) Ceilometer (clouds up to 12 km, aerosol backscatter in boundary layer) Radiosondes (Vaisala RS 92) 4 routine radiosondes per day (0, 6, 12, 18 UTC) and additional radiosondes on request (3, 9, 15, 21 UTC)

4 Statistical comparison of windprofiler LOS and radiosonde 1/2 clutter from windmill Wind vector from radiosonde projected onto windprofiler radar LOS direction (azimuth 259, elevation 75, averaging time corresponds to raso ascent time of 20 minutes, vert. resolution with oversampling 145 m, true vertical resolution 250 m) for July 2007 Statistic on difference LOS WPR -LOS Raso with 24 profiles and a total number of 886 wind speed differences

5 Statistical comparison of windprofiler LOS and radiosonde 2/2 clutter from windmill colors indicate single profiles statistical comparison (including clutter contaminated signals) mean bias = 0.08 m/s mean standard deviation = 0.61 m/s correlation coefficient r = 0.92

6 The ALADIN Airborne Demonstrator A2D A2D developed by Astrium France, Astrium Germany and DLR from , first flight in 2005 PI: Oliver Reitebuch receiver thermal hood laser receive path transmit path aircraft window Ø 200 mm Cassegrain telescope, 20 nadir angle

7 A2D Receiver Optics from Pre-Development Model Fizeau spectrometer Fabry-Perot spectrometer

8 Ray-tracing optical model of the A2D LC1 FM4 FM5 M1 Occular M2 AFRO AFRO BEX MAT AFRO RSP B MIE Path Output lens DFU MSP QWP A2D model in ZEMAX includes about 60 optical elements (e.g. lenses, beam-splitters, mirrors) Optical model was used to study and understand the images observed on Mie and Rayleigh spectrometer and its sensitivity to change of position/angle of optical elements

9 A2D Laser Optical Layout and Specifications A2D Laser Transmitter developed by Astrium, Germany and DLR Reference laser from Innolight, Germany Injection-Seeded Master Oscillator Power Amplifier MOPA Frequency-tripled using LBO Specifications energy: nm with PRF 50 Hz laser frequency shot-to-shot jitter < 4 MHz (UV), <1.3 MHz (IR) laser divergence < 100 µrad and Ø <15 mm pulse length ns size 780 x 344 x 352 mm weight 78 kg (without electronics) Schröder, Lemmerz, Reitebuch, Wirth, Wührer, Treichel (2007), Appl. Phys. B

10 A2D Laser Performance Laser frequency monitoring A2D Mie/Rayleigh receiver for N accumulated shots relative frequency for every single shot with heterodyne unit with accuracy better 100 khz absolute frequency with commercial wavemeter (High Finesse WSU-10) with MHz accuracy 1 MHz measured at IR (1.064 µm=300 THz) relative frequency stability better than 3*10-9 distance of the two resonator mirrors of 30 cm is stabilized better than 1 nm (= 1/1000 λ) Performance during second ground campaign in July 2007 energy nm divergence 200 µrad (±3σ, 99%); Ø 6 mm, M 2 =1.8 laser frequency jitter MHz (IR) rms Performance during airborne campaign in November 2007 energy nm divergence 100 µrad (±3σ, 99%);, Ø 11 mm, M 2 =1.2 laser frequency jitter below 0.5 MHz (IR) rms

11 PSD from aircraft excitation A2D laser test flights April 2007 x - axis y - axis z - axis descent before landing Major modifications after first flights in Oct 2005 Integration of new laser diodes for power amplifiers Integration of mechanical bridge between resonator mirrors Integration of new cavity control technique Ramp-Fire and Ramp-Delay-Fire instead of Pulse-Built-Up-Time-Minimization frequency [MHz] 202,5 202,0 201,5 201,0 200,5 σ f x - axis y - axis z - axis = 313 khz travel flight before descent f mean Performance during test flight April 2007 A2D laser operated seeded, single frequency during nominal flight conditions 2 different cavity control methods (Ramp-Fire and Ramp- Delay-Fire) were tested with different settings during flight Heterodyne single-shot measurements of frequency stability (requirement 1.3 MHz (IR)) were performed with the following results: Ramp-Fire: MHz (IR), 100% seeded shots, time jitter <50 ns rms Ramp-Delay Fire: MHz (IR), >99% seeded shots, time jitter <50 ns rms Even during descent with factor higher vibration levels below 200 Hz a frequency jitter of 0.5 MHz was achieved 200, time [s] Witschas, B. (2008): Master Thesis University Munich

12 532 nm laser beam of MULIS Windmill as Hard-Target for A2D

13 Stratosphere 30.2 km A2D vertical sampling schemes during second ground campaign 20.0 km Nominal 17.6 km Cirrus 16.4 km 3 different vertical sampling schemes used during second ground campaign nominal mode up to 17.6 km with highest vertical resolution (315 m) close to ground 10.0 km cirrus mode up to 16.4 km with highest vertical resolution between 8 km - 10 km => adapted in real-time with measurements from aerosol lidar MULIS stratosphere mode up to 30.2 km with resolution of 1.26 km and 2.52 km 5.0 km 2.5 km 0 km

14 A2D observations of cirrus clouds Vertical Sampling 16.4 km 2520 m 1260 m 10.0 km 630 m 315 m 630 m 5.0 km 2.5 km 0 km 1260 m

15 Intercomparison of cirrus clouds from A2D and MULIS km -7 km -0 km

16 Rayleigh radiometric performance Rayleigh atmospheric signal measured on 14./15./16. July 2007 up to 18 km Measured instrument filter transmission, quantum efficiency, radiometric gain from Astrium ( 15 parameters) Measured laser energy (60 mj) and divergence (200 µrad) from DLR End-to-end simulations with measured instrument parameters and modelled molecular backscatter profile using actual radiosonde temperature profile, modelled aerosol extinction profile (median), telescope overlap function, instrument spectral transmission parameters Mie/Rayleigh

17 Rayleigh filter transmission parameter FWHM A FWHM B Spacing B peak transmission mean July MHz 1780 MHz 6284 MHz 70% of A stand. dev. 2.6 % 2.6 % 1.4 % 1.4 % Rayleigh filter transmission curves measured frequently and analysed for FWHM, crosspoint, spacing, relative transmission A/B (fit with Airy function) Analysis of reproducibility of Rayleigh filter transmission curves and influence of different Rayleigh spectrometer temperatures, laser energy, and different timing settings for the CCD: reproducibility is 2-4 % for FWHM, and better 1% for spacing Analysis of Rayleigh response (R=A-B/A+B) slope (=sensitivity): % / MHz with an accuracy of the slope better 2 % (=8*10-6 /MHz) determined (requirement 3%)

18 Rayleigh response calibration with atmosphere , 10 GHz frequency range, 250 MHz steps B A Response: (A-B)/(A+B) per layer Linear fit: - slope - intercept - non-linear part

19 ACCD transfer times and range gate overlap Minimum range gate resolution is 2.1 µs (315 m range, 250 m 37.6 ) Transfer from image to memory zone measured as 1.1 µs; linearly for Mie and S-shape for Rayleigh with strong increase/decrease within 300 ns All 16 lines illuminated on Mie ACCD; only about 4 lines are illuminated on Rayleigh ACCD Overlap of range gates of 150 m (120 m vertical) with linear overlap function for Mie and S-shape function for Rayleigh with 45 m (36 m vertical) steep change Measurements and errors are vertically correlated Structures with strong backscatter gradients (clouds, ground return) could induce signal in adjacent range gates => height assignment uncertainty is range-gate resolution ±120 m; Significant errors measured due to non-perfect imaging of Fizeau fringe and Rayleigh spots, when strong backscatter gradients occurred, e.g. on hard-targets

20 15 Rayleigh receiver winds 2/2 A2D LOS profile of 1 observation during 14 s averaged A2D LOS profile during 6 min. Results: A2D wind observation corresponds to radiosonde and wind profiler data up to 15 km for single observations (14 s, 630 laser pulses) A2D wind random error is below 2 m/s up to 10 km altitude Wind bias in the boundary layer (0-3 km): Increased Mie signal on the Rayleigh receiver => Bias correction will be tested or retrieved Mie wind will be used in the boundary layer Receiver illumination in the near field of the telescope => not relevant for satellite ALADIN

21 Airborne ADM-Aeolus Campaigns A2D and 2-µm Wind Lidar on DLR Falcon in November 2007 Airborne test flights and campaigns A2D First functional test flights of the A2D in October 2005: 2 flights A2D laser test flights in April 2007: 2 flights First airborne campaign with the A2D and the 2-µm wind lidar in November 2007: 5 flights Objective of first airborne campaign 2-µm DWL Functional validation of operation of coherent 2-µm wind lidar and direct-detection A2D Radiometric performance for A2D in downward looking geometry with improved divergence of 100 µrad (±3σ, 99%) Obtain ground return with the A2D over flat and steep terrain and over sea with different nadir pointing angles (0, 20, 37 ) => study zero-wind calibration for satellite ALADIN

22 The DLR Falcon 20 Aircraft Falcon jet just before take-off for first A2D flight in October 2005 pressurized, twin-engine jet, max. altitude km, max. endurance 4.5 h, payload 1 t 2 bottom and 1 top optical aperture in fuselage (Ø 515 mm) for lidar payloads

23 A2D and 2-µm flight on November 28, 2007

24 Ground returns on A2D Mie receiver per observation (630 accumulated laser pulses) Flight on , (9.2 km flight altitude) from Oberpfaffenhofen crossing the Alpes to Italy (Po-valley). per measurement (18 accumulated laser pulses) 1.5 km clouds 4 km mountains A2D resolution: 315 m vertical resolution (2.1 µs) one measurement: 18 accumulated laser pulses (P=20) one observation: 630 accumulated laser pulses (N=35)

25 Ground returns on A2D Rayleigh receiver A2D: 616 km, 140 observations = 2800 measurements (à 20 pulses) Flight on , (9.2 km flight altitude) from Oberpfaffenhofen crossing the Alpes to Italy (Po-valley). 16:00-16:30 obs obs obs Satellite: 616 km, 3 observations over 200 km à 50 km (7sec) A2D resolution: 315 m vertical resolution (2.1 µs) one measurement: 18 accumulated laser pulses (P=20) one observation: 630 accumulated laser pulses (N=35)

26 Summary Second ADM-Aeolus Ground Campaign AGC-2 provided excellent dataset of nearly 300 hours of A2D observations during different atmospheric conditions (clear air, low and high winds, broken low-level clouds, mid-level clouds, cirrus clouds, stratiform clouds) Methodology of intercomparison of LOS from A2D and nearby windprofiler and aerosol lidar measurements proved to be a good approach to achieve pre-launch campaign objectives Methodology to derive winds from Rayleigh spectrometer observations consolidated and validated for every single step (calibration, background/offset corrections, derivation of response slope with non-linear part) for clear air situations future work on cloudy situations (cloud detection, Mie bias correction) future work on temporal fluctuations => stability of the instrument alignment Rayleigh radiometric performance model established and validated: very good result with an agreement of a factor of between simulations and measurements future work on Mie radiometric performance (e.g. clouds) future measurements refine the radiometric performance with A2D laser divergence below 100 µrad from ground and from aircraft Wind retrievals from Mie spectrometer started with correction of telescope obscuration

27 DLR Falcon 20 and HALO (High Altitude and Long Range Research Aircraft, modified Gulfstream G550) in April 2006 Outlook on ADM-Aeolus Campaign Activities Further 2 airborne campaigns in 2008/09 planned with the A2D and 2-µm wind lidar DLR intends to support ADM-Aeolus Cal/Val activities in 2009/2010 with ground-based campaign with the A2D, other lidars, windprofiler radar and radiosonde at DWD Lindenberg airborne campaigns with Falcon or HALO aircraft with A2D, 2-µm wind lidar and other additional payloads HALO aircraft delivery to DLR in November

28