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Supporting NOAA and NASA high-performance space-based DWL measurement objectives with a minimum cost, mass, power, and risk
approach employing Optical Autocovariance Wind Lidar (OAWL)
Christian J. Grund, Mike Lieber, Bob Pierce, Michelle Stephens, Amnon Talmor, and Carl Weimer
Ball Aerospace & Technologies Corp (BATC)
February 6, 2008
Page_2Page_2
BATC Objectives and Rationales
OAWL, OA-HSRL─ To offer broadened trade space for wind and aerosol profiling technologies addressing NOAA and NASA goals as
outlined in the NRC Decadal Survey (3D-winds, ACE, and GACM missions)─ OA approach saves mass, cost, volume, complexity, number of lasers, technical risk (e.g. can reuse
CALIPSO/MOLA/GLAS telescope design), and mission performance risk (in conjunction with an etalon receiver) Why is Ball investing in new receiver technology?
─ We believe this is an enabling approach to achieve a space mission─ Target NASA missions start in 2012 (aerosols), but the decisions for the final 3D-wind technology will probably occur in
2010 time frame. Time is now to demonstrate viability of alternatives.─ Belief: Cost, weight, power, complexity, and performance issues of current baseline need addressing.─ Community vetting and acceptance: OAWL is new, but other technologies have 15-30+ year history.
2006 internal investment Built proof of concept OAWL system and demonstrated atmospheric windReferences: Grund, ” Lidar Wind Profiling from Geostationary Orbit using Imaging Optical Autocovariance Interferometry”, WG on space-based lidar winds 7/2007, Snowmass,
COGrund, et al, “Optical Autocovariance Wind Lidar and Performance from LEO”, 7/2007 Coherent Laser Radar Conference, Snowmass, CO.
2007 internal investment Designed and modeled an achromatic, field-widened, high-resolution interferometer (1m OPD), suitable for autonomous
aircraft operation - successfully completed─ Prove OA HSRL with Proof of Concept (POC) hardware, in progress
Built comprehensive space-based OAWL radiometric performance modeling capability
2008 internal investment Fabrication of the robust, multi-wavelength OA receiver design
OAWL: Optical Autocovariance Wind Lidar - Doppler wind profilesOA-HSRL: Optical Autocovariance-High Spectral Resolution Lidar - Calibrated Aerosol Profiles
Page_3Page_3
OAWL Combines/Augments the Best Traits of Both Coherent and Incoherent Lidar Methods
Yes
Yes
Yes (UV laser)
Yes (Simple ROIC)
Maybe / Yes
Maybe
Yes (UV laser)
Yes (Difficult ROIC)
No
Some
No (IR laser)
N/A
Multi-mission Compatibilities
HSRL (calibrated aerosols/clouds)
DIAL (chemical species)
Raman (Chemical species, T, P)
Photon counting potential (GEO??)
Yes
Maybe
YesYes (integrated with etalons)
Yes / Yes
Yes
No
Maybe
Yes
No
Yes
No
Phenomenology
Measure Aerosol
Measure Molecular
Independent of Aer / Mol mixing ratio
Full precision 0-20 km profile
Yes
4 (time independent)
Yes
Yes
Yes
~4 / 15 CCD accum.
Yes
No,Maybe
No
1
No
No
Receiver
Does not need a stable reference laser
Detector elements per profile
Single multi-speckle averaging/shot
Eliminates orbital velocity correction hardware
Single/hopping OK
Yes
Single, -stable
No
Single/stable
No
Transmitter
Laser Mode
Free of absolute optical frequency lock
Direct Detection OAWL
Direct DetectionEtalons (edge/image)
Coherent Detection
Challenges
Green=positive, Red=negative, yellow=qualified Ball Aerospace & Technologies
2007 Phase 3:Design a Robust , Field-widened, Achromatic
Receiver Suitable for Airborne Testing
Page_5Page_5
Proof of Concept (POC) OAWL System Demonstrated 1 m/s Precision in Atmospheric Tests
3-Beam Interferometer
Assembly
3 Detector Assembly
Laser Transmitter Assembly
Laser Controller
Alignment Camera and Monitor
PC Data System
COTS Newtonian Receiver Telescope
0-Range, 0-Velocity Sampling Assembly
Receiver Field Stop
Channel Splitting Mirror
Stepped Mirror
Field Stop
Interferometer
Detector/ Amp 2
Detector/ Amp 3
Detector/ Amp 1
Windows PC-based Data System
(Labview) 6” dia., f/8 Newtonian Telescope
Display
3-D Sonic Anemometer
Separator Mirror
Beam Sample
Interferometer quality
Pulse Laser 100 J/pulse,
1 kHz rate
Beam Expander
IM1
IM2
Transmitter
3 physical steps
Ball Aerospace & Technologies patents pending
Demonstrated: ~1m/s precision with 0.3 s averaging and 3m range resolution in atmospheric tests at 60 m, agreeing with model predictions
POC Limitations:• Rooftop range safety limited to 100m• Low power COTS laser limits range• 50% light measured by 3 detectors: simple for POC, but not efficient• Hard to calibrate due to specific 0-phase sampling implementation
Red: OAWL (L); Anemometer-OA cross correlation (R)White: sonic anemometer (L); anemometer autocorrelation (R)Blue: cross correlation for pure Gaussian noise distributions
Brassboard system: 3 parallel interferometer architecture:
Overview of Previous Work
Page_7Page_7
New OAWL Design Uses Polarization Phase Delays and Multiplexing to Implement 4-Phase-Delay Interferometers with the Same Optical
Path
• 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 (ALADIN needs ~5 R alignment,Coherent requires telescope and <3.8Ralignment (3dB loss))
• Receiver is achromatic, allowing simultaneous multi- operations (multi-mission capable: Winds + HSRL(aerosols) + DIAL(chemistry))
• Very forgiving of telescope wavefront distortion saving cost, mass, enabling HOE optics for high resolution aerosol measurement
• 2 inputs allowing easy calibration
Ball Aerospace & Technologies patents pending
Page_8Page_8
Solid Model of Receiver (detector module covers removed)
- All aluminum construction minimizes T, cost - Athermal interferometer design
- Factory-set operational alignment for autonomous aircraft operation - ≈100% opt. eff. to detector
- multi- winds, plus HSRL and depolarization for aerosol characterization and ice/water cloud discrimination
Detectors:1 532nm depolarization1 355nm depolarization4 532nm winds/HSRL4 355nm winds/HSRL10 Total
CDR complete Dec. ‘07
Ball Aerospace & Technologies
Page_9Page_9
NASTRAN FEA Evaluation Suggests Interferometer is Robust to WB-57 Vibe Environment
Page_10Page_10
EOSyM Representation of the OA Receiver System
Coupled disturbance/ structure/ optics model built up inside EOSyM (End-to-end Optical System Model) environment.
Time simulation and frequency domain cross-checking for vibration results. Seismic mass input of disturbances in 3 directions. Structure outputs 6 optics displacements in 6 DOF to optical model. Optical model ray trace and sensitivity matrices.
Fringes & phase noise
Ball Aerospace & Technologies
Page_11Page_11
Integrated Model Process Developed at BATC
Goals:─ <6 nm (0.11 rad
phase error) vibration induced noise), 12 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
Ball Aerospace & Technologies
Page_12Page_12
Example Effect of Vibration and Thermoelastic Structural Distortion
Single pixel detection measures sum of the pupil field intensity (proportional to visibility).
Full transmission,
in phase
Zero transmission, out of phase
E=1 E=0
E=0.72 E=0.28
Visibility constant, but phase varies
Visibility degraded (integral over pupil)
+
Piston due to Doppler signal and vibration
Tilts due to Thermoelastic distortion and misalignment
Ball Aerospace & Technologies
Page_13Page_13
Visibility and Phase Noise
Visibility loss means decrease in aerosol velocity measurement optical efficiency, and HSRL aerosol/molecular signal separation.
Phase noise emulates wind-induced phase shift of return signal; unimportant to HSRL
max min
max min
I IV
I I
Pre-flight calibration goal Imax (envelope)
= Visibility = Contrast
Change due to thermoelastic distortion
Change of phase error due to structural vibration during time-of-flight
Flight operating point (slowly drifting)Long period
Short period
Ball Aerospace & Technologies
Page_14Page_14
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
40/ 20 nm, 20 Hz isolators added, WC/ nom
8.5/ 6 nm, redesigned structure, WC/ nom
WC = Worst case
Requirement:<1m/s/shot/100 sRandom dynamic error with WB-57 excitation
Final design Prediction Feb. 2008 : 6nm RMS jitter, exceeding spec and meeting goal, suggests performance dominated by SNR not environment
Thermal results: model verifies design is athermal wrt average temperature
Ball Aerospace & Technologies
Page_15Page_15
In Progress and Proposed Efforts to Raise TRL to 5,6
2008 Internally Funded Objective: Fabricate OA Receiver Suitable for aircraft flight testing In-Progress
Status: Optical design PDR - complete Sep. 2007 Receiver CDR - complete Dec. 2007 Receiver design /performance modeled - complete Jan. 2008 Major components to fabrication – in progress Feb. 2008 System Assembled/ preliminary testing - planned Aug. 2008
Proposals submitted: NASA ROSES Instrument Incubator Program:
─ PI Grund (Ball), OA winds. Raise TRL for winds from WB-57, complete OA as a system, flight plan to pass over many wind profiler network sites, potential ground lidar near Boulder, land and ocean
─ PI Hostetler (NASA LaRC), OA HSRL. Alternative interferometer approach for multi-wavelength HSRL, data collected could be processed for winds, no special corroborative winds in current plan
LOOKING FOR OTHER INTERESTS and POSSIBILITIES
Ball Aerospace & Technologies
Page_16Page_16
FUTURE CRAD-Proposed Implementation for WB-57
6’ Pallet(WB-57 form factor)
Pallet Cover
Custom Pallet-Mounting Frame
Telescope
Custom Window
IRAD-Built Receiver
Laser Source
Ball Aerospace & Technologies
Practical OA performance from Space
Page_18Page_18
Comprehensive LEO Performance Model Implemented for Realistic Components
LEO Model Parameters:
Wavelength 355 nm
Pulse Energy 550 mJ
Pulse rate 50 Hz
Receiver diameter 1m (single beam)
LOS angle with vertical 450
Vector crossing angle 900
Horizontal resolution* 70 km (500 shots)
System transmission 0.35
Alignment error 5 R average
(NOTE: ~50 R allowed)
Background bandwidth 35 pm
Orbit altitude 400 km
Vertical resolution 0-2 km, 250m
2-12 km, 500m
12-20 km, 1 km
Phenomenology CALIPSO model
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
Validated CALIPSO Backscatter model used.
Model calculations validated against short range POC measurements.
Ball Aerospace & Technologies
Page_19Page_19
OAWL Daytime Space-based Performance OPD 1m, optimized for aerosols
Waveform signal processing and 4-channel architecture implemented
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
“Objective” Margin
“Thres/Demo” Margin
Cloud free LOS
Ball Aerospace & Technologies
Page_20Page_20
Evaluating Cloud Impacts on OA Wind Accuracy: 1st Cut
No biases due to aerosol to molecular backscatter mixing ratio clouds induce no velocity biases Sliding range gate feasible independence from range-backscatter weighting errors Every shot 0-referenced no dependence on changes in laser spectrum over shot averaging time Gradual degradation as signals decrease due to opaque cloud fraction or translucent cloud OD:
If ODmargin = ODcloud that degrades velocity precision to the available margin then, for OAWL:─ ODmargin for “objective” performance is ~0.46─ ODmargin for “demo/target” performance is ~0.81
Conclusions: for the OA model assumptions, if the LOS cloud attenuation over profile integration time averages to: OD<0.46, then objective requirements are still met 100% in the PBL OD<0.81, then demo/threshold requirements are still met 100% in the PBL For OD>0.81, performance degrades slowly with effective cloud OD as per above equation
Running an OSSE would be a good next step to include global statistics.
N
i
iRODcloudeN
V
1
),(2 error(R) velocity Ensemble Where N is the number of shots in the profile average,
ODcloud is the optical depth of the cloud in each shot above the altitude of interest, and V is the cloud free velocity error. (might apply to all direct detection lidars if SNR behaves)
Ball Aerospace & Technologies
Integrated Direct Detection (IDD) Lidarfor Aerosol and Molecular Backscatter Winds
Page_22Page_22
Aerosol WindsLower atmosphere profile
A Single-laser All Direct Detection Solution: Couple OAWL and Etalon receivers
Integrated Direct Detection (IDD) wind lidar approach: OAWL uses most of the aerosol component, rejects molecular. OAWL HSRL retrieval determines residual aerosol/molecular mixing ratio Etalon backend processes molecular backscatter winds, corrected by HSRL Result:
─ single-laser transmitter, single wavelength system─ 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
Ball Aerospace & Technologies
Page_23Page_23
IDD Receiver vs. ALADIN
ALADIN Approach:
Common Rec/Trans Telescope
355nm Laser
Shutter Fizeau Fringe-Imaging Aerosol Receiver
Double-Edge Etalon
Molecular Receiver
CCD Accumulation
Profiling Detectors
Proposed OAWL/Etalon IDD Approach:
Very small FOV and high receiver /transmitter alignment tolerance are drivenby Fizeau resolution and background light accumulation in detectors. High wavefront quality needed to support small FOV. Precludes HOE scanner/telescope.
QE advantage but signal accumulation precludes per-shot corrections; frequency stability of laser must extend over shot accumulation time.
Receiver Telescope
355nm Laser
Field-widened OAWL Aerosol Receiver
Double-Edge Etalon
Molecular Receiver Per-shot profiling Detectors
Per-shot profiling Detectors
Field-widening supports:• CALIPSO quality telescope • HOE scanner/telescope• Wide rec/trans. alignment tolerance
Shot-resolved detectors support:• Simplified laser• minimized background light• photon-counting, sliding range gate• software-only LOS velocity correction• detector system redundancy
Ball Aerospace & Technologies
Preliminary Mission Technology Assessment
Page_25Page_25
Assumptions: Telescope and Scanner
Coherent Detection
Double-Edge Direct
Det.Hybrid
Fringe-Imaging
OADD IntegratedOA+ Double-
edge
Telescope1m, CALIPSO-like 3 7 2 7 7 7
RMS WF (632 nm) 0.3 4 4 4 4 4Mass(kg) ~60 for WF 35 60 35 35 35
TRL 3 7 3 7 7 74 fixed telescopes/optics
Mass(kg) 208 150 208 150 150 150TRL 7 5 7 5 5 5
1.4m mirror+driveMass(kg)/Vol(L) +65 for WF 40 65 40 40 40
TRL 3 3 3 3 3 3HOE Scanner/telescope
TRL not feasible 3(4) NA 3(4) 3(4) 3(4)Mass (kg) not feasible 20 NA 20 20 20
Electrical power(W) not feasible 25 NA 25 25 25
Component
Scanner
WAG’s: Seeking opportunities to work with others on refinementsPerhaps publicizing ISAL’s would be useful
Ball Aerospace & Technologies
Note: Entries in red are chosen for optimal architecture comparisons
Page_26Page_26
Assumptions: Laser
Coherent Detection
Double-Edge Direct Det.
HybridFringe-Imaging
OA
Integrated DD
OA+ Double-edge
TRL 3 3 3 3 3 3Injection seeding needed yes maybe yes yes no maybe
Frequency lock yes maybe yes yes no maybeComplexity high low-med high med low low-med
number of SS lasers 4 2-4 6-8 2-4 2 2-4Mass(kg) 15 25 40 25 25 25
Electrical Power
360* (2 m) (10Hz,0.25J,WPE:1.4%)
1100* (355nm)(50Hz, 0.55J,WPE: 3.2%) 1460 1100 1100 1100
Component
Technology
Laser
WAG’s: Seeking opportunities to work with others on refinementsPerhaps publicizing ISAL’s would be helpful
* Laser performance based on Azita Valinia “Discussion of DWL Airborne Campaigns” on the LWG site
Ball Aerospace & Technologies
Note: Entries in red are chosen for optimal architecture comparisons
Page_27Page_27
Assumptions: Receiver and Misc, Overall Risks
Coherent Detection
Double-Edge Direct
Det.Hybrid
Fringe-Imaging
OA
Integrated DD
OA+ Double-edge
TRL 4 4(5) 4(5) 4 3(4,5) 3(4,5)mass(kg) 15 10 30 15 15 25
power (W) 30 15 45 20 15 25Calibration complexity low low low high low low
OtherStructure Mass(kg) 20 20 40 20 20 25
Overall RisksCost risk high low high med med low*
Schedule risk med low med low low low*Technical risk med low med med med low*
Component
Technology
Receiver(+data system)
WAG’s: Seeking opportunities to work with others on refinementsPerhaps publicizing ISAL’s would be useful
*presumes OA receiver under construction performs as expected
Ball Aerospace & Technologies
Notes: Entries in red are chosen for optimal architecture comparisons.
Page_28Page_28
Assumptions: Optimal Architecture Comparisons
Note: 2 complete transmitters assumed, no receiver redundancy
Possibly unnecessary
Hybrid
InjectionLaser
TransmiterLaser (2m)
InjectionLaser
TransmiterLaser (355 nm)
Double-edgeEtalon receiver
4 Fixed-pointing Telescopes
0.5m, 0.25 waves
Coherent receiver T/R
Commutator
355
nm
/ 2
m
Bea
m C
om
bin
er
Integrated DD (IDD)Injection
LaserTransmitter
Laser (355 nm)
Double-edgeEtalon receiver
1 HOE Telescope/Scanner1m, 355nm, 2 wavesOAWL
receiver
Fringe Imaging DDInjection
LaserTransmitter
Laser (355 nm)
Fringe-ImagingEtalon receiver
1 HOE Telescope/Scanner1m, 355nm, 2 waves
Ball Aerospace & Technologies
Page_29Page_29
Mass, Power, Risk, Relative Cost Comparison
Fringe-Imaging Only
Hybrid (Coherent,Fringe Image or Double-Edge)
Integrated DD OA+ Double-
edge
Relative Mass** 0.31 1 0.33Relative Power 0.78 1 0.78Relative Volume 0.7 1 0.75Relative cost 0.5 1 0.5Technology risk 0.8 1 0.8Cost risk 0.5 1 0.5Schedule risk 0.8 1 0.8Performance risk 1.5 1 1Mission Risk 1.2 1 0.8
Criteria
Best System PerformanceOAWL risk reducers vs. Fringe Imaging:
• 4 Separate detectors redundancy (2 min)
• IDD: separate aerosol and molecular receivers
• immune to loss of laser frequency control
• shot-shot correction immune to spectral shape
• high sensitivity to aerosol when present without needing correction
OAWL risk reducers vs. Coherent:• Laser technology readiness (schedule, cost)• Immunity to loss of laser frequency control• Large optics quality requirements (cost, mass)• No hardware correction for spacecraft LOS V required• Can use HOE telescope/scanner (cost, mass, ~power) • Can also provide multi- HSRL (mission cost or technology development cost share?)
Ball Aerospace & Technologies
**assumes fully redundant lasers
Conclusions and Plans
Page_31Page_31
Conclusions: OAWL Progress and Plans
• OAWL has achieved TRL 3 with a proof of concept brassboard system that demonstrated atmospheric wind measurements to ~1 m/s, consistent with expectation.
• A comprehensive model predicting space-based OAWL winds and HSRL performance with realistic components has been built and validated by POC measurements and CALIPSO data.
• The space-based model predicts cloudy and cloud free OAWL performance competitive with the coherent detection component of the hybrid without requiring a separate laser and system.
• A robust, achromatic, field-widened OAWL receiver has been designed and evaluated using Ball’s end-to-end integrated modeling capabilities. The integrated model predicts performance exceeding requirements for aircraft testing in the WB-57
• A 355nm/532nm operable, ruggedized, field-widened OAWL receiver suitable for flexible lidar system integration and high altitude aircraft testing is under construction (planned completion ~Sept. ’08) – we are actively seeking partnerships and funding opportunities to rapidly advance the technology to TRL 5-6.
• IIP proposals submitted for integration and airborne testing and validation of a full OAWL lidar and separately, for an OA-HSRL demonstration (winds testing not supported at this time). If successful, the proposed efforts will bring OA to TRL-5, and support shake and bake receiver testing as well.
• OAWL winds from GEO developments will continue in 2008 with realistic scenario modeling including full geometry.
Ball Aerospace & Technologies
Page_32Page_32
Conclusions: Space-based Lidar Winds Architecture
Given:• A clear-air profiling capability is a necessity for meeting 3D-winds availability, requiring:
Rayleigh molecular backscatter measurement with a short wavelength laser a powerful laser transmitter operating in the visible to near UV at a minimum
• 3D-winds precision in the lower atmosphere requires aerosol backscatter measurement
Then:• An OAWL and double-edge Integrated Direct Detection (IDD) wind lidar architecture can meet or exceed hybrid performance with a single laser transmitter while reducing mission cost by ~50%, mass by ~67%, and power by ~22%, and at reduced schedule, cost, and performance risks.
• An OA receiver is potentially suitable for multiple missions specified in the Decadal Survey, offering multiple cost sharing opportunities
Ball Aerospace & Technologies
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