an alternative direct detection approach to doppler winds that is independent of aerosol mixing...
TRANSCRIPT
An Alternative Direct Detection Approach to Doppler Winds that is
Independent of Aerosol Mixing Ratio and Transmitter Frequency Jitter
Ball Aerospace & Technologies Corp.
Presented by: Chris Grund [email protected], 303-939-7217
Presented to: Space Winds Lidar Working GroupMiami, Florida
2/8/2007
OAWL Theory
3
Optical Autocovariance TheoryOptical Autocovariance Theory
V = * * c / (4 * (d2-d1))
Optical Autocovariance Wind Lidar:
OAWLPronounced: ALL
50 40 30 20 10 0 10 20 30 40 500
0.5
1
1.5
2
2.5
Wavelength Shift (m/s)
Backscatter (W)
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
Stepped mirror
BeamSplitter
0 200 400 600 800 10000
0.2
0.4
0.6
0.8
1
Distance d2-d1
Arb
itra
ry I
nten
sity
CH 1
CH 3
CH 2
CH 2CH 1
CH 3
Doppler shiftedAtmosphericReturn at t>0
Laser at t=0
M W
ings
A+MAerosol +center of molecular
ReceiverTelescope
Doppler ShiftDue to wind
AM
A+M+BG
BG
Return spectrum from aMonochromatic source
Measured as a fraction
Pre
filte
r
Note: Scale of molecuar and cycle of autocovariance function are arbitraqry for illustration
4
OAWLOAWL Advantages Advantages
Laser simplifications:
• Injection seeding not necessary
• Shot to shot mode hopping no problem
• Passive Q-switch feasible – no HV
• No 800 km coherence length LO needed
• No hardware correction for spacecraft V
Receiver:
• One system for whole atmosphere
• Aerosol and molecular in one
• No calibration dependence on targets
• Mixed aerosols, clouds, molecules OK
• No clean/dirty air calibration bias
• No absolute frequency lock to laser
• No absolute temperature controllers
• No spectral drift calibration requirement
OAWL OAWL does it ALLdoes it ALL
5
OAWL Combines/Augments the Best Traits of Both OAWL Combines/Augments the Best Traits of Both Coherent and Incoherent Lidar MethodsCoherent and Incoherent Lidar Methods
Yes
Yes
Yes (UV laser)
Yes
Maybe/Yes
Maybe
Yes (UV laser)
Yes
No
Some
No (IR laser)
N/A
Synergies/Compatibilities
HSRL (calibrated aerosols/clouds)
DIAL (chemical species)
Raman (Chemical species, T, P)
Photon counting potential (next time!)
Yes
Yes
No
Yes
Yes
Yes
Yes
No
Yes
No
No
No
Phenomenology
Measure Aerosol
Measure Molecular
Sensitive to Aer/Mol mixing ratio
Full precision 0-20 km profile
None
3(6)
Yes
No
None
Many
Yes
Maybe
>800 km
1
No
Yes
Receiver
Reference laser coherence length
Detector Elements
Single multi-speckle averaging/shot
Orbital velocity correction in hardware
Single/hopping OK
No
Single/stable
Yes
Single/stable
Yes
Transmitter
Laser Mode
Absolute frequency lock
Direct Detection OAWL
Direct DetectionEtalons (edge/image)
Coherent Detection
Challenges
Brassboard Development
7
Demonstration System ArchitectureDemonstration System Architecture
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 μJ /pulse, 1 kHz rate
Beam Expander
IM1
2IM
Transmitter
8
The Brassboard SystemThe Brassboard System
3-BeamInterferometer
Assembly
3 DetectorAssembly
Laser TransmitterAssembly
Laser Controller
Alignment Camera and Monitor
PC Data System
COTS NewtonianReceiver Telescope
0-Range, 0-VelocitySampling Assembly
Receiver Field Stop
Channel Splitting Mirror
9
Development Team Development Team
Mick Cermak – Lab and fabrication support, experiment support and logistics
Dina Demara – Data system software
Doug Frazier – brassboard mechanical design
Dennis Gallagher – final brassboard optical design and modeling (left Ball in ’06)
Chris Grund – PI, system and experiment design, signal processing, calibration, validation
Bob Pierce – ongoing optical engineering, experiment support
Ron Schwiesow – proposed original concept (retired from Ball 10/05)
Michelle Stephens – Spaceborne performance modeling
Steve Stone – Procurement assistance, electronics support
Internal R&D funding support through Ray Demara gratefully acknowledged
Proof of Concept Testing
11
Proof of Concept Test RangeProof of Concept Test Range
OAWL System in Lab
Turning Mirror
Sonic Anemometer
Focal volume
Lidar beam pathTerminal Beam Block
FA Cleanroom Building Rooftop at Ball Aerospace in Boulder, CO
12
First light – Experimental Intensity SNRFirst light – Experimental Intensity SNR
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
0.45
-50 0 50 100 150 200 250
Range (m)
Volts from detector
0-range sample(wire works asdesigned for cal)
Molecular+aerosol scattering
Terminal range - black targetat 90 m
Focus range60 m
60m SNR on atmosphere:13 dB optical (26 dB elec.)(expect 11 dB = validates model within
backscatter and detector uncertainty)
Conditions:1 kHz rep rate16 shot average (7 dB single shot)full sun daytime/filter inthrough interferometer3-beams to 1 detectorblack illustration board targetBW: 150 MHz* No field stop
RMS Noise0.0073V
Signal0.15V
0-range0-velocitysample
13
First OAWL POC Wind RetrievalsFirst OAWL POC Wind Retrievals(December 2006) (December 2006)
Red: Anemometer-OA cross correlation White: anemometer autocorrelationBlue: cross correlation for pure Gaussian noise distributions
~1 m/s random error with ~0.6 m/s bias demonstrated with 0.3 s averaging and 3m range resolution. Excellent fluctuation correlations.
14
First Wind Retrievals- continuedFirst Wind Retrievals- continued
Statistically very different wind set (see anemometer autocorrelation function)• again excellent fluctuation correlations• OAWL brassboard: ~1.2 m/s random error, with 0.15 m/s bias (3m res, 0.3 s avg)
Preliminary
OAWL Space Lidar Winds
Performance Modeling
16
Performance Requirements Addressed (so far)Performance Requirements Addressed (so far)for OAWL Space Wind Lidar Operationfor OAWL Space Wind Lidar Operation
From: Kavaya and Gentry: Status of Laser/Lidar Working Group Requirements
Demo Threshold Objective
Vertical depth of regard (DOR) 0-20 0-20 0-30 km
Vertical resolution: Tropopause to top of DOR Top of BL to tropopause (~12 km) Surface to top of BL (~2 km)
Not Req.21
Not Req.1
0.5
20.5
0.25
kmkmkm
Horizontal resolution 350 350 100 km
Velocity error Above BL In BL
32
32
21
m/sm/s
Minimum wind measurement success rate 50 50 50 %
17
Preliminary OAWL System PerformancePreliminary OAWL System Performancefor Spaceborne Operationsfor Spaceborne Operations
Conditions:Wavelength 355 nmPulse Energy 550 mJ Pulse rate 50 HzReceiver diameter 1mLOS angle with vertical 450
Vector crossing angle 900
Horizontal resolution 350 kmOPD 1 mSystem transmission 0.35Alignment error 5 μRBackground bandwidth 35 pmOrbit altitude 400 kmVertical resolution 1 kmPhenomenology CALIPSO model
0 0.5 1 1.5 2 2.5 30
5
10
15
20
altitude (km)
Velocity error (m/sec)
Daytim
e
Nig
httim
e
Horizontal Wind Velocity Error (m/s)
A
ltit
ud
e (
km)
Objective
Demo&
Threshold
Wrap-up
19
ConclusionsConclusions
Optical Autocovariance Wind Lidar (OAWL) has advantages for space operations
Potentially, one system DOES IT ALL, from and boundary layer to free trop
Simpler laser
• Injection seeding not needed, passive Q-sw feasible
• single mode per pulse, but pulse to pulse frequency hopping OK
No velocity calibration dependence on aerosol/molecular backscatter mixing ratio
Laser coherence length only needs to exceed the interferometer path length
Compatibility with secondary aerosol or chemical species missions
First OAWL brassboard lidar completed, aligned, and calibrated in 2006
Developments ongoing, intercomparison campaign sought (NOAA, NASA)
Successful, range-resolved atmospheric proof of concept tests completed
Preliminary wind retrieval/calibration algorithms developed/working
Measurements validate brassboard system performance model and hardware
20
What’s in the works?What’s in the works?
Improved 0-velocity, 0-range sampling apparatus in progress for brassboard
Ruggedizing and field enclosure for brassboard cross-validation
Field test alongside existing wind lidar system. Perhaps the NOAA/ETL HRDL system.
Design (in progress this year) and construction (next year?$$$) of a ruggedized, field-widened receiver suitable for aircraft testing, environmental testing to achieve TRL 6
Evaluating laser scaling issues and options.
Extensive performance model development based on the validated CALIPSO model, but including detailed OAWL components, wind mission scenarios, and spacecraft interactions.