Lessons learnt for Aeolus from the pre-launch validation campaigns with the A2D Uwe Marksteiner, Oliver Reitebuch, Benjamin Witschas, Christian Lemmerz, Stephan Rahm DLR German Aerospace Center , Institute of Atmospheric Physics , Oberpfaffenhofen , Germany
Objectives of A2D (ALADIN Airborne Demonstrator) Validation of ALADIN instrument with atmospheric signals before launch Derivation of conclusions for: retrieval algorithms on-ground and in-orbit tests verification and calibration of satellite instrument HuricaneHiRes_credits-ESA_ATG-Medialab Acknowledgement: Funding for the development of the ALADIN Airborne Demonstrator A2D and performance of campaigns was provided by ESA and DLR. Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 2
Comparison of Aeolus and A2D A2D (ALADIN Airborne Demonstrator): • „ twin instrument “ ( receiver, detector , …) • space industry performs test and characterisation in laboratory • DLR performs also atmospheric measurements • viewing geometry comparable to Aeolus • possibility of ground detection A2D is particularly suited to verify the wind measurement & calibration strategy of Aeolus Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 3
The ALADIN airborne demonstrator • Development of the A2D with the optical receiver and laser breadboard from ESA ´ s Pre-Development A2D receiver thermal hood Programme • Delivery of A2D and first flights of a direct-detection Doppler lidar worldwide in 2005 • Ground campaigns in 2006 and 2007 2-µm DWL electronic rack • First flights of coherent and direct- detection wind lidar on-board the same A2D aircraft in 2007 telescope 10 years of experience with A2D 2-µm Doppler wind lidar Payload in DLR Falcon aircraft during campaigns in 2007, 2008 & 2009 Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 4
A2D hardware The optical receivers of the airborne demonstrator from DLR (A2D) and the satellite instrument (ALADIN) are based on almost identical design Fabry-Perot Interferometer Novel technology 1. combined arrangement of two different spectrometers 2. Fizeau spectrometer for Mie channel 3. sequential implementation of Fabry Perot interferometers Fizeau 4. custom-built ADM Interferometer Reitebuch et al. 2009 specific ACCD chip Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 5
3 rd Aeolus campaign in Sept. 2009 10 flights with a duration of 33 hours including transfer and test flight Reasons for choice of Iceland/Greenland low aerosol load pure Ray. scatter jet-stream high wind speeds ice albedo calibration as Aeolus ocean change of reflexion Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 6
3 rd Aeolus campaign in Sept. 2009 26 km 6 min 2 calibrations wind observations Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 7
Instrument Response Calibrations of A2D Internal Reference wind speeds 2 calibration curves almost on top of each other Cal.1 ≈ 3 m/s Cal.2 ⇒ Apparently very consistent calibrations. However, resulting in differences in wind speeds of up to ≈ 4 m/s. Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 8
Ground calibration ⇒ summation of signal • Ground echo signal distributed over 2 „ range-gates “ intensity • deviations depending on non- perfect location of Rayleigh spots and Mie fringe on ACCD and range-gate overlap • in this case calibration curves of single „ range-gates “ are partly deviating by ≈120 m/s ≈ 120 m/s ⇒ preceding summation of signal yields a useful calibration curve relative frequency / MHz Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 9
Distributed ground echo & range-gate overlap 100 ratio in % 18 s (ca. 3.5 km) detector 300 - 2400 m Comparison of detected ground height: A2D Digital Elevation Model terrain 1 µs ≈ 150 m ground (integration) Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner time 10
Line-Of-Sight wind and corrections 0 v ( f f ) 2 v v LOS wind , A I LOS A C , / ZWC Additionally induced „virtual“ wind speed, e.g. due to: 1. component of aircraft velocity in direction of LOS (know) 2. Instrumental error or error in flight attitude (unknown) v A/C v ZWC v LOS,A/C -v A/C ground does not move signal must yield 0 m/s Zero-Wind Correction Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 11
1 st airborne measurements of 2 different lidars in 2009 A2D (Rayleigh) 30 min wind measurement 2-µm lidar jet-stream cloud A2D (Mie) 368 km Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 12
Airborne lidar observations and ECMWF model ECMWF 2-µm MODIS, Oct. 1 st , 2009 Mie Rayleigh Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 13
Statistical comparison for ALADIN airborne demonstrator against 2-µm lidar Rayleigh Mie slope: 1.04 slope: 1.14 std. dev.: 2.5 m/s std. dev.: 1.5 m/s # of points: 596 # of points: 932 Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 14
Ongoing study on A2D instrumental noise sources • An ideal (photon) counting process obeys Poisson statistics • For Aeolus it is expected, that all instrumental noise sources are so small that Poisson Noise is the largest contributor („ shot noise limited detection “) 4700 Noise study for A2D to investigate instrumental errors: Background/(LSB) - trend corrected 4600 4500 4400 • A2D is Poisson noise 4300 Signal Int.A limited in regarding Poisson Noise Int.A BKG mean = 4464 LSB mean Int_A = 33471 ± 689 ( Poisson = 106) Signal Int.B 4200 mean Int_B = 30087 ± 624 ( Poisson = 100) the background signal Poisson Noise Int.B 36000 Poisson = 38.4 LSB 4100 intensity ⇒ no 35000 4000 0 200 400 600 800 1000 increased electronic time/(s) intensity/(LSB) (internal) 34000 900 BKG noise = 42.3 LSB 800 33000 700 32000 600 • signal intensity of the 500 counts 31000 Internal Reference 400 300 30000 Poisson noise limited 200 29000 up to 40 s 100 28000 0 4300 4350 4400 4450 4500 4550 4600 0 1000 2000 3000 4000 5000 6000 Background signal/(LSB) time/(s) Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 15
Summary and Conclusion Experience of more than 10 years with operation of the unique A2D instrument New methods & new wind retrieval algorithms were developed using A2D data from airborne and ground measurements High quality wind measurements Principle of calibration and wind retrieval for Aeolus was validated with airborne demonstrator A2D at DLR during several ground and airborne campaigns The A2D will be used after launch for validation of Aeolus wind measurement and calibration strategy Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 16
Aeolus Cal/Val – ESA ESRIN – February 10 th , 2015 – Uwe Marksteiner 17
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