OAWL IIP Development Status: Year 2.0
C.J. Grund, S. Tucker, J. Howell, M. Ostaszewski, and R. Pierce, Ball Aerospace & Technologies Corp. (BATC), [email protected]
1600 Commerce St. Boulder, CO 80303
Working Group on Space-based Lidar WindsBar Harbor, MEAugust 24, 2010
Agility to Innovate, Strength to Deliver
Ball Aerospace & Technologies Corp.
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Acknowledgements
The OAWL Development Team:
Sara Tucker – Technical Manager, Signal Processing, Algorithms
Bill Good (Jim Howell) – Systems Engineer, Aircraft specialist
Tom Delker, Bob Pierce – Optical engineering
Miro Ostaszewski – Mechanical Engineering
Mike Atkins (Kelly Kanizay) – Electronics Engineering
Dan Ringoen - (Rick Battistelli), (Dina Demara) – Software Engineering
Mike Lieber – Integrated system modeling
Paul Kaptchen – Technician
Chris Grund – PI, system architecture, science/systems/algorithm guidance
OAWL Lidar system development and flight demo supported by NASA ESTO IIP grant: IIP-07-0054
Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Aeronautics and Space Administration.
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Aerosol WindsLower atmosphere profile
Addressing the Decadal Survey 3D-Winds Mission withAn Efficient Single-laser All Direct Detection Solution
Integrated Direct Detection (IDD) wind lidar approach: Etalon (double-edge) uses the molecular component, but largely reflects the aerosol. OAWL measures the aerosol Doppler shift with high precision; etalon removes molecular backscatter reducing
shot noise OAWL HSRL retrieval determines residual aerosol/molecular mixing ratio in etalon receiver, improving
molecular precision Result:
─ single-laser transmitter, single wavelength system, telescope driven by DD requirements not coherent detection─ single simple, low power and mass signal processor─ full atmospheric profile using aerosol and molecular backscatter signals
Ball Aerospace patents pending
Telescope
UV Laser
Combined Signal
Processing
HSRL Aer/mol mixing ratio
OAWL Aerosol Receiver
Etalon Molecular Receiver
Molecular WindsUpper atmosphere profile
1011101100Full
Atmospheric Profile Data
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Velocity precision (m/s)
Alt
itu
de
Coheren
t
DWL
Etalon DD
DWL
1 2 3
0
5km
10
15
2
0IDD = OAWL+Etalon
Hybrid = Coherent+Etalon
Potential Performance Envelope
Note: notional approximation etalon+coherent hybrid approach
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Purpose for OAWL Development and Demonstration
OAWL is a potential enabler for reducing mission cost and schedule─ Aerosol wind precision similar to 2-mm coherent Doppler, but requires no additional laser─ Accuracy not sensitive to aerosol/molecular backscatter mixing ratio ─ Tolerance to wavefront error allows simpler (and heritage) telescope and optics─ Compatible with single wavelength holographic scanner allowing adaptive targeting─ Wide potential field of view allows relaxed tolerance alignments, similar to CALIPSO─ FOV ~120 mR feasible while supporting 109 spectral resolution ─ Minimal laser frequency stability requirements─ LOS spacecraft velocity correction without needing active laser tuning
Opens up multiple mission possibilities including multi-l HSRL, DIAL compatibility
Challenges met by Ball OAWL approach─ Elimination of control loops while achieving 109 spectral resolution─ Thermally and mechanically stable, meter-class OPD, compact interferometer─ High optical efficiency (~97%)─ Simultaneous high spectral resolution and large area*solid angle acceptance providing practical
system operational tolerances with large collection optics
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Optical Autocovariance Wind Lidar (OAWL) Development Program
Internal investment to develop the OAWL theory and implementable flight-path
architecture and processes, performance model, perform proof of concept
experiments, and design and construct a flight path receiver prototype.
NASA IIP: take OAWL receiver as input at TRL-3, build into a robust lidar system,
fly validations on the WB-57, exit at TRL-5.
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Ball OAWL Receiver Design Uses Polarization Multiplexing to Create 4 Perfectly Tracking Interferometers
• Mach-Zehnder-like interferometer allows 100% light detection on 4 detectors
• Cat’s-eyes field-widen and preserve interference parity allowing wide alignment tolerance, practical simple telescope optics, and high spectral resolution
• Receiver is achromatic, facilitating simultaneous multi-l operations (multi-mission capable: Winds + HSRL(aerosols) + DIAL(chemistry))
• Very forgiving of telescope wavefront distortion saving cost, mass, enabling HOE optics for scanning and aerosol measurement
• 2 input ports facilitating 0-calibrationpatents pending
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Completed Receiver / Permanently Potted Alignments(except for the final beamsplitter)
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OAWL IRAD Receiver Development Status
Receiver Status: Optical design PDR complete Sep. 2007 Receiver CDR complete Dec. 2007 Receiver performance modeled complete Jan. 2008 Design complete Mar. 2008 COTS Optics procurement complete Apr. 2008 Major component fabrication complete Jun. 2008
(IIP begins------------------------------------------------------------------------ Jul. 2008) Custom optics procurement vendor issues Aug. 2008
─ Custom optics procurement complete Dec. 2008
─ Accommodating rework complete Jan. 2009
Interferometric optics/mount bonding complete Feb. 2009 Interferometric alignment bond tests shrinkage / thermal issues Feb. 2009
─ New materials/process/mount design complete May, 2009
Assembly and Alignment complete Oct. 2009 Preliminary testing complete Oct. 2009 Delivery to IIP complete Nov. 2009
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OAWL System: NASA IIP
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OAWL IIP Objectives
Develop and Demonstrate an OAWL DWL system designed to be directly scalable to a
space-based 3D-Winds lidar mission.
Provide IRAD-developed receiver to IIP (entry TRL 3): Functional demonstrator for OAWL flight path receiver design principles and assembly processes.
Shake & Bake Receiver: Validate receiver design approach and fabrication techniques suitable for airborne vibe environment.
Integrate the OAWL receiver into a complete lidar system: add laser, telescope, frame, data system, isolation, and autonomous control software suitable for operation in a WB-57 pallet.
Raise OAWL technology to TRL 4 through ground validations alongside the a NOAA coherent Doppler lidar system.
Raise OAWL technology to TRL 5 through high altitude aircraft flight demonstrations.
Validate radiometric performance model as risk reduction for a flight design.
Validate the integrated system model as risk reduction for a flight design.
Provide a technology roadmap to TRL7
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Receiver Vibration Testing - Acquisition
Receiver and mounts instrumented with multiple accelerometers(blue wires)
WB-57 Taxi, takeoff and landing (TTOL) shock/vibe level testing (1.78 gRMS) showed the adjustable beamsplitter needed staking to prevent alignment drifts, but the permanent interferometer alignment potting method appears stable at these levels.
Operational vibe (0.08 gRMS) effects are within expectations; not expected to affect WB-57 wind measurement performance
Audio speaker used to excite on organ pipe mode within the interferometer to repeatably sample the whole phase space.
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Integrated Model Process Developed at BATC
Goals:─ <6 nm (0.11 rad
phase error) vibration induced noise), 30 nm accep.
─ <5% visibility reduction due to thermoelastic distortions.
Main system modeling outputs
─ Fringe visibility─ Phase noise
Code V SolidWorks
NASTRAN
Aircraft PSD
6
References:
M. Lieber, C. Weimer, M. Stephens, R. Demara, “Development of a validated end-to-end model for space-based lidar systems”, in SPIE vol 6681, U.N.Singh, Lidar Remote Sensing for Environmental Monitoring VIII, Aug 2007.
M. Lieber, C. Randall, L. Ayari, N. Schneider, T. Holden, S. Osterman, L. Arboneaux, "System verification of the JMEX mission residual motion requirements with integrated modeling", SPIE 5899, Aug 2005.
M. Lieber, C. Noecker, S. Kilston, “Integrated system modeling for evaluating the coronagraph approach to planet detection”, SPIE V4860, Aug 2002
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Integrated Model – Design Iteration:Vibration-Induced Phase Noise Convergence on Specification
1 2 3 4 50
0.5
1
1.5
2
2.5
3
3.5
Lo
g O
PD
(n
m)
1900 nm, initial hard mount
55/ 27 nm, 20 Hz isolators added, WC/ nom
12/ 8.5 nm, redesigned structure, WC/ nom
WC = Worst case
Requirement:<1m/s/shot/100 msRandom dynamic error with WB-57 excitation(12nm, goal 8.5nm)
Final design Prediction Feb. 2008 : 8.5 nm RMS jitter, exceeding req. and meeting goal, suggests performance dominated by intensity SNR, not vibration environment
While current result does not match the original model predictions, the receiver was modified to include the plate beamsplitter, and the FEM has not yet been integrated into the model. Also, real measurements have a small amount of measurement noise that is not accounted in the model.
Conservative application of an appropriate MUF: the model and modeling process appear validated.
IIP Upshot: ~6000 pulse returns (30s) will be averaged per wind profile suggesting the operational
vibe induced errors appear to be <~0.03 m/s (10 km range) per profile therefore not significant for IIP
Current result: ~17/34 nm RMS (10/20 km ranges)
Model Uncertainty Factor (MUF) for similar analysis modeling based on comments from Gary Mosier GSFC
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Summary of effective velocity error due to measured response to simulated WB-57 vibe environment
Vibe axis
OPD Standard Deviation
(10/20 km)
Velocity precision- per shot
Precision w/ 1-second averaging
Precision w/ 30-second averaging
X 15/31 nm 2.3/4.6 m/s 16/33 cm/s 3/6 cm/s
Y 19/38 nm 2.8/5.6 m/s 20/40 cm/s 3.7/7.4 cm/s
Z 7/13 nm 1.0/2.0 m/s 7/14 cm/s 1.3/2.6 cm/s
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IIP System Integration Design for WB-57 Pallet
The OAWL system is integrated in the WB-57 aircraft using one pressurized 6 foot pallet
The pallet houses the optical system, electronics, and thermal control
OAWL Optical SystemPallet
Flight Direction
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OAWL Pallet Configuration
1. Laser Power Supply
Pallet Frame
Double Window
Laser
Wire Rope Vibration Isolators
Telescope Primary Mirror
Sub-Bench with Depolarization Detector
Receiver
Telescope Secondary Mirror
Chiller
Optic Bench
3. Data Acquisition Unit4. Separate suspension system
2. Power Condition Unit
Electronics Rack
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OAWL Transceiver Optical System
Ball Aerospace & Technologies
Interferometer Detectors (10)
Telescope
Laser
Zero-Time/OACF Phase Pulse Pre-Filter
Field Stop and FocusCoaxial Bistatic R/T Alignment
Likely etalon location for complete IDD molecular/aerosol DWL
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OAWL IIP System – Asssembled and Aligned
Temporary Laser(50 mJ/pulse, 523 nm)X
Temporary Laser(2.5 mJ/pulse, 532 nm)
3 ns pulse5X bandwidthX
7 months delay in the primary laser delivery led to several attempts to use surrogate lasers to shake out integrated system bugs – the October WB-57 clock is ticking
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Beam Expander
Coating damage on the secondary due to 355nm pulse energy --- different coating vendor met specs
Other issues addressedincluded:
• pulse width• pulse energy• bandwidth• waveplate
function• residual 1 mm
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Complete IIP OAWL DWL System
Fibertek laser installed and aligned
T0
To atm
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Pre-ground-validation Full System First Light Rooftop Tests (532nm)
T0 Wideband (pulse) optical quadrature (~32 MHz, measured)
T0 (local)
T600ns (90m range hard target)
20s Record of Raw 4-channel Signals
Demonstrates OAWL receiver and laser transmitter are working well together (with a plane wavefront)
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Pre-ground-validation Full System First Light Rooftop Tests (532nm)
T0
T600ns
Ph
ase
p
-pSeconds
Target Tracks T0 Auto-covariance Phase
T0 ~80%
T600ns ~20%Deminished due to poor Near-range overlap, and
Co
ntr
ast
T0 (reminder)
Ph
ase
p
-p
T0 -T600ns
1-sec average
a field-widening alignment issue under investigation
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OAWL IIP Status Summary
Program start, TRL 3 complete Jul. 2008 TRL-3
IRAD receiver delivered to IIP complete Nov. 2009
Receiver shake and bake (WB-57 level) complete Nov. 2009
System PDR/CDR complete Feb./Mar. 2009
Lidar system design/fab/integration complete Jul. 2010
Ground validations completed planned Oct. 2010 TRL-4
Airborne validations complete (TRL-5) planned Dec. 2010 TRL-5
tech road mapping (through TRL7) planned May 2011
IIP Complete June 2011
Current Status
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Leg 1Leg 2Multipass
** Wind profilers in NOAA operational network
Platteville, CO
Boulder, CO Houston, TX
OAWL Validation Field Experiments Plan
1. Ground-based-looking up Side-by-side with the NOAA mini-MOPA
Doppler Lidar
2. Airborne OAWL vs. Ground-based Wind Profilers and mini-MOPA
15 km altitude looking down along 45° slant path (to inside of turns.
Variety of meteorological and cloud
conditions over land and water
September 2010
October 2010
NOAA mini-MOPACoherent Doppler Lidar
OAWL System
Some curtailment of planned flight hours is in planning due to WB-57 cost increases, certification details, lack of complete pallet info , and pallet mods .
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OAWL and NOAA mini-MOPA comparison site(ASAP after the integration tests are complete)
General plan: LOS comparisons between OAWL and NOAA’s
mini-MOPA Doppler lidar. OAWL
─ Will be located inside the newly rebuilt Table Mountain T2 building
─ Enclosed facility with 2 windows providing eastern and northern/northeastern views
mini-MOPA (longer performance comparison range)
─ Container on trailer parked outside.─ LOS pointing may be interspersed with VAD
scans to provide contextual wind information
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Conclusions
The dual-wavelength, field-widened, OAWL receiver has been successfully completed and delivered to the IIP for lidar system integration.
Receiver testing showed that the receiver tolerates WB-57 Taxi, Takeoff, and Landing shock and vibe, and the data suggest that the receiver can actually operate with reduced performance under these extreme conditions.
The receiver performs near expectations during operational vibe conditions.
The IIP lidar system has been fully assembled with final laser, aligned.
First light acheived. Autocovariance phase from hard target tracks T0 phase.
Testing and final alignments are in progress in prep for validations.
Ground validations testing expected in September 2010. These are critical precursors to flight execution (TRL 4).
Aircraft plans in place and flight conops understood.
WB-57 flight tests remain on track for October 2010 (TRL 5)Ball Aerospace & Technologies
Backups
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Data System Overview
Data system architecture─ Based on National Instruments PXI Chassis─ Utilizes COTS Hardware
Challenges & Solutions─ Reduced air pressure at altitude degrades heat removal
ability of stock cooling fansUpgrade cooling fansTest system in altitude chamber
─ Jacket material used in COTS cables is PVC, which is not permitted on WB-57Utilizing NI terminal strip accessories where possibleFabricating cables made from allowable jacket materials
─ Data Flow ~ 0.6 GB/minuteNew 256 GB SSD
Ball Aerospace & Technologies
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On/Off line DIAL wavelength jump typically 10’s GHz
Optical Autocovariance lidar (OAL) approach - Theory
No moving parts / Not fringe imaging Allows Frequency hopping w/o re-tuning Simultaneous multi- l operation
Optical Autocovariance Wind Lidar (OAWL):Velocity from OACF Phase: V = l *Df * c / (2 * (OPD)) OA- High Spectral Resolution Lidar (OA-HSRL): A = Sa * CaA + Sm * CmA , Q = Sa * CaQ + Sm * CmQ
Yields: Volume extinction cross section, Backscatter phase function, Volume Backscatter Cross section, from OACF Amplitude
Pulse Laser
d2
d1
Det
ecto
r 1
Det
ecto
r 2
Det
ecto
r 3 Data System
CH 1
CH 3
CH 2
From Atmosphere
Phase Delay mirror
BeamSplitter
ReceiverTelescope
Pre
filte
rOPD=d2-d1
Simplest OAL(Not the IIP config)
Frequency
Df = phase shift as fraction of OACF cycle
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Ball Space-based OA Radiometric Performance Model –Model Parameters Using : Realistic Components and Atmosphere
LEO Parameters WB-57 Parameters
Wavelength 355 nm, 532 nm
355 nm, 532 nm
Pulse Energy 550 mJ
30 mJ, 20 mJ
Pulse rate 50 Hz
200 Hz
Receiver diameter 1m (single beam)
310 mm
LOS angle with vertical 450
45°
Vector crossing angle 900
single LOS
Horizontal resolution* 70 km (500 shots)
~10 km (33 s, 6600 shots)
System transmission 0.35
0.35
Alignment error 5 mR average
15 mR
Background bandwidth 35 pm
50 pm
System altitude 400 km
top of plot profile
Vertical resolution 0-2 km, 250m
100m (15m recorded)
2-12 km, 500m
12-20 km, 1 km
Phenomenology CALIPSO model
CALIPSO model
l-scaled validated CALIPSO Backscatter model used. (l-4 molecular, l-1.2 aerosol)
Model calculations validated against short range POC measurements.
10-8
10-7
10-6
10-5
10-4
0
5
10
15
20
backscatter coefficient at 355 nm m-1 sr-1A
ltitu
de, k
m
aerosol
molecular
Volume backscatter cross section at 355 nm (m-1sr-1)A
ltit
ud
e (
km)
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OAWL – Space-based Performance: Daytime, OPD 1m, aerosol backscatter component, cloud free LOS
0
2
4
6
8
10
12
14
16
18
20
0.1 1 10 100Projected Horizontal Velocity Precision (m/s)
Alt
itu
de
(km
)
355 nm
532 nm
Demo and Threshold
Objective
Threshold/Demo Mission Requirements
250 m
500 m
1km
Ver
tica
l Ave
rag
ing
(R
eso
luti
on
)
Objective Mission Requirements
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Looking Down from the WB-57 (Daytime, 45°, 33s avg, 6600 shots)
0
2
4
6
8
10
12
14
16
18
0 0.1 0.2 0.3 0.4 0.5 0.6
Velocity Precision (m/s)
Alti
tude
(km
)
355nm532nm