GEO Spacecraft Development

1
An Alternative Direct Detection Approach to
Doppler Winds that is Independent of Aerosol
Mixing Ratio and Transmitter Frequency
JitterBall Aerospace Technologies
Corp.Presented by Chris Grund
cgrund_at_ball.com, 303-939-7217Presented to
Space Winds Lidar Working GroupMiami,
Florida2/8/2007
2

• OAWL Theory

3
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




1
2
3
Data


System

Detector
Detector
Detector
V l Df c / (4 (d2-d1))
Measured as a fraction
Optical Autocovariance Wind Lidar OAWL Pronounced
ALL
Note Scale of molecuar and cycle of
autocovariance function are arbitraqry for
illustration
4
OAWL 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 does it ALL
5
OAWL Combines/Augments the Best Traits of Both
Coherent and Incoherent Lidar Methods
6

• Brassboard Development

7
Demonstration System Architecture
8
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
9
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 RD funding support through Ray Demara
  gratefully acknowledged

10

• Proof of Concept Testing

11
Proof of Concept Test Range
12
First light Experimental Intensity SNR
0-range 0-velocity sample
13
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
14
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)

15

• Preliminary
• OAWL Space Lidar Winds
• Performance Modeling

16
Performance Requirements Addressed (so far)for
OAWL Space Wind Lidar Operation
17
Preliminary OAWL System Performancefor
Spaceborne Operations
Conditions 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 350 km OPD
1 m System transmission
0.35 Alignment error 5 mR Background
bandwidth 35 pm Orbit altitude
400 km Vertical resolution 1
km Phenomenology CALIPSO model
Objective
Daytime
Nighttime
Altitude (km)
Demo Threshold
Horizontal Wind Velocity Error (m/s)
18

• Wrap-up

19
Conclusions

• 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
Whats 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.