GEO Spacecraft Development

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Optical Autocovariance Wind Lidar and Performance
from LEO Chris Grund, Michelle Stephens, Carl
Weimer Ball Aerospace Technologies Corp
cgrund_at_ball.com, 303-939-7217Presented to
Coherent Laser Radar ConferenceSnowmass,
Colorado7/10/2007
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Optical Autocovariance Theory
Pulse Laser
Doppler Shift Due to wind
d

1
CH 3

Return spectrum from a Monochromatic source

From

CH 2

Prefilter
Atmosphere


CH 1


Receiver Telescope

Stepped

d

2
mirror




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2
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Data


System

Detector
Detector
Detector
V l Df c / (4 (d2-d1))
Measured as a fraction
Optical Autocovariance Wind Lidar OAWL Pronounced
ALL Ball Aerospace patent pending
Note Scale of molecuar and cycle of
autocovariance function are arbitraqry for
illustration
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OAWL Advantages

• Laser simplifications
• Injection seeding not necessary
• Shot to shot mode hopping no problem
• Passive Q-switch feasible no HV
• 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
• No reference laser needed
• IF the SNR is high enough or the molecular
  region velocity precision requirement is modest

OAWL does it ALL
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OAWL Combines/Augments the Best Traits of Both
Coherent and Incoherent Lidar Methods
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• Brassboard Development

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Demonstration System Architecture
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The Brassboard System
Channel Splitting Mirror
Alignment Camera and Monitor
3 Detector Assembly
PC Data System
3-Beam Interferometer Assembly
COTS Newtonian Receiver Telescope
Laser Controller
Receiver Field Stop
Laser Transmitter Assembly
0-Range, 0-Velocity Sampling Assembly
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• Proof of Concept Testing

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Proof of Concept Test Range
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First light Experimental Intensity SNR
0-range 0-velocity sample
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First OAWL POC Wind Retrievals(December 2006)
1 m/s random error with 0.6 m/s bias
demonstrated with 0.3 s averaging and 3m range
resolution. Excellent fluctuation correlations.
Red Anemometer-OA cross correlation White
anemometer autocorrelation Blue cross
correlation for pure Gaussian noise distributions
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First 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)

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• Preliminary
• OAWL Space Lidar Winds
• Performance Modeling

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Performance Requirements Addressed (so far)for
OAWL Space Wind Lidar Operation
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Comprehensive LEO Performance Model Implemented
for Realistic Components
LEO Model Parameters (unless otherwise
noted) Wavelength 355 nm Pulse
Energy 550 mJ Pulse rate
50 Hz Receiver diameter 1m LOS angle
with vertical 450 Vector crossing angle
900 Horizontal resolution 70 km
(10 s avg) System transmission
0.35 Alignment error 5 mR Background
bandwidth 35 pm Orbit altitude
400 km Vertical resolution 0-2 km,
500m 2-12 km, 1km 12-20 km, 2
km Phenomenology CALIPSO model Architecture
3-det. OAWL
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Small OPD ? Molecular and Aerosol contribute, but
cannot meet needs with current laser technology
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Small OPD Molecular and Aerosol can meet needs
over most of the atmosphere with single system,
but requires 10J/pulse (500W), or 4.5m dia.
telescope, or better detector, or combo
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Large OPD ? Aerosol Onlyperformance rivals
coherent detection hybrid subsystem, but
molecular unresolved
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Compromise Single-laser Solution Couple OAWL and
Etalon receivers
Molecular Winds?Upper atmosphere profile
OAWL Aerosol Receiver
Etalon Molecular Receiver
Combined Signal Processing
Telescope
1011101100
Full Atmospheric Profile Data
HSRL? Aer/mol mixing ratio
UV Laser
Aerosol Winds? Lower atmosphere profile

• 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 patent applied for

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• Wrap-up

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Technical Conclusions 1

• Optical Autocovariance Wind Lidar (OAWL) has
  advantages for space operations
• Potentially, one laser system DOES IT ALL, from
  and boundary layer thru the free troposphere
• Simpler laser
• Injection seeding not needed, passive Q-switching
  feasible (no HV)
• single mode per pulse needed, but pulse to pulse
  frequency hopping OK
• No velocity calibration dependence on
  aerosol/molecular backscatter mixing ratio
• No reference laser required pulse coherence
  length need only exceed the interferometer OPD
  (best if range resolution bin length)
• Easy compatibility with secondary aerosol or
  chemical species missions
• To achieve desired molecular signal precision
  with an all OAWL system requires more laser power
  than currently practical

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Technical Conclusions 2

• First OAWL brassboard lidar completed, aligned,
  calibrated.
• Preliminary wind retrieval/calibration algorithms
  developed/working
• Successful, range-resolved atmospheric proof of
  concept tests completed.
• Combining an etalon back end with an OAWL front
  end allows full atmospheric profiling with
  desired precision, using a single laser and a
  single, simple, low power signal processor.
• Next week in Snowmass presenting concept,
  applications, and performance of imaging,
  photon-counting OAWL (IPC/OAWL) wind lidar from
  GEO at the space wind lidar working group

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Whats in the works?

• Technical Developments
• Simultaneous wind and HSRL Proof of Concept tests
  (this year, in progress)
• Model performance of an integrated OAWL and
  Etalon receiver wind system
• Improved 0-velocity, 0-range sampling apparatus
  in progress for brassboard
• Cross validation field test alongside existing
  wind lidar system. Perhaps the NOAA/ETL HRDL
  system.
• Evaluating laser scaling issues and options for
  space.
• Mission concepts
• Developing 100X100 pixel imaging, photon-counting
  OAWL for winds from GEO (talk next week at the
  Space-based Wind Lidar Working Group Meeting
  preliminary concept and feasibility for winds
  from GEO)
• Extensive integrated performance model
  development based on the validated CALIPSO model,
  but including detailed OAWL components, wind
  mission scenarios, and spacecraft interactions.
• Design (in progress this year) and construction
  (next year?) of a ruggedized, field-widened
  receiver suitable for vibe and environmental
  environmental testing to achieve TRL 6, and a
  potential aircraft validation mission.

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Ball OA 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
• James Lasnick purchasing and experiment
  logistics support
• Bob Pierce ongoing optical engineering,
  experiment support
• Ron Schwiesow proposed original concept
  (retired from Ball 10/05)
• Steve Stone Procurement assistance, electronics
  support
• Michelle Stephens Spaceborne performance
  modeling
• Carl Weimer Space systems and Space
  performance modeling (CALIPSO experience)
• Internal RD funding support through Ray Demara
  gratefully acknowledged