GEO Spacecraft Development

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Lidar Wind Profiling from Geostationary Orbit
using Imaging Optical Autocovariance
Interferometry Chris Grund Ball Aerospace
Technologies Corp cgrund_at_ball.com,
303-939-7217Presented to Space Winds Lidar
Working GroupSnowmass, Colorado7/17/2007
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LEOs Hard EnoughWhy Winds from GEO?

• GEO and LEO wind missions are Complementary
• LEO global, high vertical resolution, polar
  regions, intermittent local coverage, best at
  tweaking medium-long range prediction models
• GEO regional, 24/7 near-realtime observations,
  best for supporting severe storm nowcasting, high
  density updates in critical tropical cyclone
  steering regions, upper level sheer, tracking
  rapidly evolving short waves, and supporting eddy
  flux measurements. Dwells on areas of short range
  forecast uncertainty.
• GEO wind lidar benefits
• Nowcasting of severe storms, rapid flow
  deformation/ vorticity concentration? lower false
  alarms / geographically pin point tornado
  touchdown areas
• Does not need hydrometeors to trace flow ? Clear
  air streamline curvature.
• Fimely obs in steering regions ? Improved
  hurricane landfall and intensity prediction

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Imaging Photon Counting Optical Autocovariance
Wind Lidar (IPC/OAWL) Concept with 1 Transmitter
and 1 or more Independent Receivers
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GEO Wind Lidar Characteristics

• Simple staring system, no scanning or multiple
  telescope switching needed.
• Long integration perfect for photon counting but
  needs the right technology to make feasible
  (OAWL is enabling)
• Sees through broken cloud, large footprint,
  long-duration observations
• Graceful degradation in partially cloudy regions
  (fewer lost shots)
• Full-time real-time coverage of Pacific coast
  storms, Atlantic storms, Central Canada
• Combine with passive or DIAL profiling chemical
  sensing ? fluxes at regional and national
  boundaries
• 1 transmitter can service several receivers,
  simultaneous parallax obs
• Temporal averaging inherently smoothes winds for
  direct incorporation in models (not single point
  or a narrow line average)
• Inherent 2-D horizontal spatial average improves
  wind fidelity over oceans
• Crude pointing sufficient. Use co-boresighted
  camera to navigate.

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• OAWL Theory

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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




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 Ball Aerospace patent pending
Note Scale of molecuar and cycle of
autocovariance function are arbitraqry for
illustration
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• OAWL Proof of Concept

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Demonstration System Architecture
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Proof of Concept 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 Test Range
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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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• Modeled OAWL Performance From LEO - Review

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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 LOS
angle with vertical 450 Vector crossing
angle 900 Horizontal resolution
70 km System transmission
0.35 Alignment error 5 mR 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
CALIPSO Backscatter model
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Small OPD ? Molecular and Aerosol contribute, but
cannot meet needs with current laser technology
Modeling by Michelle Stephens
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Large OPD ? Aerosol Onlyperformance rivals
coherent detection hybrid subsystem, but
molecular unresolved
Modeling by Michelle Stephens
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• OAWL Enables Winds from GEO

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OAWL Enabling Characteristics for GEO Wind
Mission

• Simple intensity measurements yield winds
• Ideally suited to photon counting at low rates
• Simple all digital 1-bit pipelined shift
  register ROIC architecture
• works well with 0-phase correction enabling
  in-phase ACF averaging
• Modest processing requirements enable low data
  rate com
• Michelson imaging interferometry known art
  (heritage)
• Because OA is immune to frequency hopping, easy
  to add DIAL
• without affecting wind measurements
  (fluxes, pollution transport)
• High Spectral Resolution Lidar calibrated
  aerosol optical properties
• available without additional hardware (just
  processing same data)-
• --- of interest to passive radiometry trace gas
  retrievals also

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Imaging Photon Counting Optical Autocovariance
Wind Lidar (IPC/OAWL)
Beamshaper
UV Laser Single mode (but not single f)
0-Phase Sampling Optics
CH1
Field-widened OA Interferometer
Narrow Optical Bandpass Filter
Telescope (4 m, fixed pointing)
CH3
CH2
10k profiles/ 20 min
Signal Processing
Sum to Memory
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IPC/OAWL Leads to Very Simple All Digital ROIC
Modest Signal Processing
e.g. Photocathode/MCP Geiger Mode APD
100 X 100 element Detector Layer
Bump Bonding
ROIC
Address Calculator
Readout Clock
Shift Register
0-Phase Calculation
Shot Clock 50 Hz
Range Clock (MHz)
Add to Memory
Memory
Modest Computer 200k profiles / 20 min
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Preliminary IPC/OAWL Feasibility Modeling from GEO

• Evaluation
• Ecnts 0.3 /shot/bin/ pixel/ channel
• A 1J/pulse, 50 Hz laser (50W) ? 6104 shots in
  20 min. ? 1680 photons/bin/pixel
• (SNR 40)
• 4.5m aperture (similar to proposed for GEO DIAL
  by Ismail, et al)? SNR160

R Range (3.6106 m) E0 Transmitted pulse energy
(1 J) Ecnts measured energy in photon
counts/shot/bin x optical and quantum system
efficiency (0.25) Ar area of the receiver
telescope (4 m2, 2.25 m dia.) DR range bin width
(1 km) bp backscatter cross section at range
(510-6 m-1sr-1) T 1-way transmission to range
(0.9) Npixels Number of pixels in array
(10k) Nchannels Number of interferometer
channels (3) / pixel h Plancks constant
(6.610-34 J/s) l wavelength (355 nm (532 nm a
trade))
Suggests 2 m/s precision feasible from GEO!
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• GEO Mission Applications

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Winds Missions

• Combined NexRad and IPC/OAWL in GEO both clear
  air stream flow and hydrometeor tracing in cloudy
  regions of severe storms
• High precision severe storm warnings
• Extended warning times
• OAWL winds OAWL HSRL Passive trace gas
  profiling
• Trace gas flux transport across regional, state,
  and national boundaries
• Visibility measurement and forecasting
• Accurate regional moisture flux for convective
  storm and rainfall (flooding) forecasts
• Climate source and sink studies
• OAWL HSRL aerosol extinction corrects passive
  radiometry
• OAWL winds OAWL HSRL DIAL trace gas sensing
  Depolarization
• Similar to above but higher altitude resolution
  and precision
• High precision eddy correlation fluxes over land
  and oceans
• DIAL, Depolarization, and OAWL can use the same
  laser wavelength hopping no problem
• Cloud ice/water discrimination
• Shared large aperture telescope

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• Wrap-Up

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OAWL Technical Advantages

• Receiver
• Simple imaging / processing architecture
• 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

• 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

• Measurement Synergies
• HSRL aerosols w/o added hardware
• DIAL Need only wavelength hoping laser

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Conclusions

• OAWL simplifies wind lidar systems and laser
  transmitters in LEO or GEO
• GEO provides significant complimentary
  measurements to LEO missions
• Profiles where and when needed for Tropical
  Cyclone intensity and accurate track forecasting
  . 72 updates/24 hrs exactly where needed. Shear
  over TCs.
• Rapid convergence of vorticity, deformation in
  clear air (radar needs hydrometeors)
• Pinpoint severe storm predictions, earlier
  tornado warning times, nowcasting
• High temporal density wind soundings off coasts
• OAWL is enabling for a wind mission from GEO
  (simple photon counting architecture)
• GEO Mission Feasible to achieve better than 2
  m/s precision, with 75 km horizontal and 1 km
  vertical resolution, over a 7500 x 7500 km area
  with 20 minute time resolution with currently
  conceived and demonstrated component
  technologies.
• OAWL is enabling for combined wind, HSRL and
  DIAL missions with no added hardware
• Modest processing requirements lead to low data
  rate com requirements