1. Lidar winds from GEO: The Photons to Winds Conversion Efficiency
Ball Aerospace &
Technologies Corp.
Lidar winds from GEO: The Photons to Winds Conversion Efficiency
Christian J. Grund, and Jim Eraker Ball Aerospace & Technologies Corp. (BATC), Dave Emmitt
Simpson Weather Associates,
Bruce Gentry
Goddard Space Flight Center,
Response to questions raised at the Working Group on Space-based Lidar Winds in Bar Harbor, ME August 24, 2010
Agility to Innovate, Strength to Deliver

2. Areas for System Comparison
Photon Transmitter
Laser- energy, rep rate, pulse width, wavelength
Optics- throughput, beam diameter, beam pointing
signal
Geometry- range, angle thru atmosphere, altitude resolution
Backscatter- scatterer type, backscatter cross section
Extinction- integrated aerosol and molecular, clouds
Background light- solar/view angles, scatterer optics, attenuation
Turbulence- refractive and kenetic (spectral)
Phenomenology
Optical
noise
Photon Receiver
Geometry- collection area, FOV
Optical- throughput, bandwidth
Key to discrepancies
Converter
Detector
Spectral Analyzer
Signal Processor
Efficiency- Photons in / wind precision out
(inc. analyzer leverage and detection noise)
Resolution-Temporal, spatial
Performance

3. Initial Comparison Assumptions
Parameter
GLO (DD etalon)
GEOWindSat (OAWL)
Dawn-like (Coherent)
CALIPSO (DD)
Wavelength nm
355
532
2150
Pulse energy J
1.5 1
0.5
0.11
Rep rate Hz
100 10 20
Pulse bandwidth MHz 25
1.6
multimode
Transmit x
Assume0.9
0.9
Assume 0.8
Photons out / s *1019 32 24
4.3
0.53
Range Mm 38
0.7 (LEO)
Altitude for comparison km 3
Altitude Res km
0.250
0.0075
Look angle deg
LOS
Scatterer type
molecules
aerosols
Aerosols and molecules
Optical depth
0.3
0.05 NA
Background W/nm/sr
Turbulence refractive
Background photons / s
Turbulence spectral
Telescope diameter m 2
0.15
Receive x
0.016
0.31
FOV mrad ? 30 5
130
Optical Bandwidth pm
10??
10e-4 (10 MHz (search)) 37
Analyzer Photon x / 1m/s
2.52e6
1300
Time resolution s
1200
0.1
No data just hyperbole

4. Baseline from CALIPSO radiometric modeling assumed for Comparison
Radiometric Backscatter and Extinction Assumptions (this is a ratio in the comparison so
Baseline from CALIPSO radiometric modeling assumed for Comparison
GEOWindSat
GLO
Transmission to 3 km altitude:
355nm 0.4
532nm 0.8

5. 1st Order Radiometric Analysis and Result
1.3
2.2
129
5.2*10-4
6.4*10-2
Advantage GLO
Advantage GEOWindSat
Net Single Beam Advantage to GEOWindSat
(but comparable performance)

6. Symbols Phot_trans transmitted photons/pulse
Phenom effect of atmospheric backscatter and transmission
Phot_rec photon collection scalling factor
Conv conversion efficiency from photons to LOS speed
xtrans transmitter optical efficiency
E0 pulse energy
bp volume backscatter cross section
R Range
xrec receiver optical efficiency
Ar area of the receiver
DR range averaging bin in measurement
T 1-way atmospheric transmission
PRR pulse repetition rate
Tavg independent measurement averaging time
Xphot-to-V number of photons at the detector needed for 1 m/s precision
c speed of light
h Planck’s constant

7. Conclusion Radiometric controversy resolved by this note
GEOWindSat and GLO have comparable performance even though the telescope size is vastly different
The main factors are photon to velocity conversion efficiency and Averaging CONOPS
GLO assumes an etalon discriminator using Doppler broadened molecular backscatter and the optical throughput of an etalon filter
GEOWindSat uses narrow bandwidth aerosol backscatter and the high throughput OA interferometer
GLO measures for a short time and moves on
GEOWindSat dwells for 20 min and may use multiple electronically targetable fov’s
Radiometric controversy resolved by this note
Other issues for another time:
refractive index effects on measurement altitude and position
daytime background light
conops and meteorological relevance
An OAWL at 1 mm with newer detectors might be a good trade

8. Backups

9. GEOWinds Observatory predicted horizontal wind precision (satellite at -45° lon)
Accessible
Region
73° S
Mature model.
Assumptions: 16 simultaneous pixels, 20 minute integration at 3 km altitude in daylight.

10. Observatory Performance over Field of Regard
21 range bins/profile are assumed producing the indicated altitude resolution.

11. Potential Optical Refraction Effects on Altitude Assignment Uncertainties
Beam height refractive deflection for typical cell in FOR and 87o from local nadir.

12. GEO-OAWL Hardware Components – Confluence of Multiple Recent Technology Developments
Electrically Steerable Flash Lidar (ESFL) –
Subject of Carl Weimer’s current NASA ESTO IIP
(Desdyni focus) (1J/pulse OK, 90X90 independent beamlets OK)
355nm, 0.5 – 1J/pulse, 100 Hz (current tech)
Independently retargetable beams
No momentum compensation
Electronic Beam forming and steering
AOM
Laser
Subject of Ball IRAD development
and current NASA ESTO IIP demonstration
(3D Winds focus)
Patent pending
Patents pending
4-phase
Field-widened
OAWL Receiver
Fixed-pointing
Wide-Field
Receiver
Telescope (~3°X3°)
Subject of Ball IRAD development
for high-sensitivity and resolution flash lidar and low- light passive astrophysical imaging (Intensified Imaging Photon Counting (I2PC) FPA).
New. Top level hypothetical architecture block diagram, no data
4 Photon counting Profiling,Flash Lidar Imaging Arrays
Co-boresighted
camera to geo-locate pixels from topographic outlines
Patent pending
ESFL allows targeting with high spatial resolution and adaptive cloud avoidance
Ball Aerospace & Technologies