Mid-term status of the TWiLiTE direct
detection Doppler lidar development program
Bruce Gentry1, M. McGill1, G. Schwemmer6, M. Hardesty2, A.
Brewer2, T. Wilkerson5, R. Atlas2, M.Sirota3, S. Lindemann4, F.
Hovis7
1NASA
GSFC; 2NOAA; 3Sigma Space Corp.; 4Michigan Aerospace Corp.;
5Space Dynamics Lab; 6SESI, 7Fibertek Inc
Working Group on Space-Based Lidar Winds
July 17-20, 2007
Snowmass, CO
CLRC July 2007
Outline
•
•
•
•
TWiLiTE Overview
Requirements and Performance Simulations
Instrument Subsystem Status
Summary
CLRC July 2007
Technology Maturity Roadmap
Past Funding
Laser Risk Reduction Program
2-Micron Coherent Doppler Lidar
2 micron
laser
1988
Diode Pump
Technology
1993
Autonomous
Oper. Technol.
Aircraft
Operation
Diode Pump
Technology
Lifetime
Validation
Space
Qualif.
Conductive
Cooling Techn.
1999
Inj. Seeding
Technology
Compact
Packaging
2005
Demo
Space
Qualif.
Lifetime
Validation
Conductive
Cooling Techn.
Packaged Lidar
Ground Demo.
2007
Pre-Launch
Validation
UAV Operation
Autonomous
Oper. Technol.
2008 (Direct)
1 micron
laser
High Energy
Technology
1997
Inj. Seeding
Technology
1996
IIP-2004 Projects
Operational
Pre-Launch
Validation
High Energy
Laser
Technology
Compact Laser
Packaging
2007
Compact Molecular
Doppler Receiver
2007
0.355-Micron Direct Doppler Lidar
CLRC July 2007
Tropospheric Wind Lidar Technology Experiment
(TWiLiTE) Instrument Incubator Program
• TWiLiTE will demonstrate, for
the first time, downward looking
wind profiles from 18 km to the
surface obtained with an
airborne direct detection
scanning Doppler lidar
• The TWiLiTE instrument is
compact, rugged and designed Rotating HOE
for autonomous operation on the telescope
NASA WB57.
Doppler Receiver
• TWiLiTE will be completed in
summer 2008.
• The instrument could be
transitioned to a UAV like Global
Hawk .
UV Laser
TWiLiTE system integrated on WB57 3 foot pallet
CLRC July 2007
Airborne Doppler Lidar Wind Profiling
250 m
Lidar ranging permits determination of wind speed as a function of altitude.
Multiple look angles permit determination of vector wind.
CLRC July 2007
TWiLiTE Target Platform
WB57 Aircraft: NASA Johnson Space Center
Specification
WB57
Max. Altitude
18 km
Duration
6.5 hours
Cruise Speed
200 m/s @ 18 km
Payload mass
374 kg per pallet X
4 pallets.
Payload Electrical
Power
110V, 4 X 25A, 3
phase, 400 Hz; 28V
DC 35A
Payload mounting
Modular pallet
Nadir view
3’ instrument pallet
CLRC July 2007
TWiLiTE Measurement Requirements
Parameter
WB57
Velocity accuracy (HLOS projected) (m/s)
2.0
Range of regard (km)
0-18
Vertical resolution (km)
0.25
Horizontal resolution (km) (complete scan cycle)
25
Groundspeed (m/s)
200
Nadir angle (deg)
45
Scan pattern
Up to 16 pt step-stare
Horizontal integration per LOS (seconds)//ground
track (km)
10//2
CLRC July 2007
TWiLiTE Instrument Parameters
Wavelength
354.7 nm
Telescope/Scanner Area
0.08 m2
Laser Linewidth (FWHH)
150 MHz
Laser Energy/Pulse (6 W)
30 mJ @ 200 pps
(8 W)
40 mJ @ 200 pps
Etalon FSR
16.65 GHz
Etalon FWHH
2.84 GHz
Edge Channel Separation
6.64 GHz
Locking Channel Separation
4.74 GHz
Interference filter BW (FWHH)
120 pm
PMT Quantum Efficiency
25%
Optical Efficiency (Edge w/o BS
or etalon)
0.37
BS
0.41
CLRC July 2007
Photocounts Detected in each Edge Channel
10 sec (2000 shot) integration; z=250 m; 45 deg nadir
107
detected photons
black = overlap corrected, no max. count rate
blue = overlap corrected, 50 MHz max. count rate
106
105
104
0
5
10
Altitude (km)
15
20
Includes effects of lidar overlap function and the use of 3 PMTs sharing the
incoming signal in the ratio 90:9:1 to increase linear counting dynamic range.
CLRC July 2007
TWILITE system performance
Simulated L-O-S wind error
20
Current system performance (red curve) includes
telescope with 58% diffraction efficiency and 55%
encircled energy.
In both cases, the black curve is the performance
with no solar background included.
15
Altitude (km)
Expected system performance (blue curve) includes
telescope with 62% diffraction efficiency and 82%
encircled energy.
10
5
red = performance with current system parameters
blue = performance with expected system parameters
0
0.0 0.5 1.0 1.5 2.0
L-O-S wind error (m/s)
CLRC July 2007
8 point conical step stare scan pattern
Aircraft motion
Top view
Scanning parameters:
• Constant dwell of 10s/LOS
• Fixed azimuth increments
of 45 deg in CW steps
Radial HLOS wind speed
measured in a single range bin for
3 cycles of the 8 point step stare
scan pattern. Assumes constant
velocity (maximum = 40 m/s)
CLRC July 2007
TWiLiTE Direct Detection Wind Lidar
Key Technologies
Entrance Exit TRL
TRL
4
• High spectral
resolution all solid state
laser transmitter
5-6
• High spectral
resolution optical filters
4
5-6
• Efficient 355 nm
photon counting
molecular Doppler
receiver technologies
4
5-6
• Novel UV Holographic 3
Optical Element
telescopes and
scanning optics
5-6
CLRC July 2007
Double Edge Etalon Channels
CLRC July 2007
Triple Aperture Step Etalon - Michigan
Aerospace Corp
Steps in etalon resonant
frequency are created by
vapor deposition of fused
silica on one plate.
Full Field Fringe Pattern
CLRC July 2007
TWiLiTE Receiver Design Summary
• Volume reduced by 90% versus current GLOW receiver
• Optical path lengths minimized to improve mechanical, thermal
stability
• End-to-end throughput increased by 60%
• Signal dynamic range increased by 2 orders of magnitude
CLRC July 2007
Assembled Receiver Components
CLRC July 2007
TWiLiTE Holographic Telescope
FUNCTIONS
• Collect and focus laser
backscatter
• Scan laser and FOV
• Provide pointing knowledge
to CDH
FEATURES
• Primary Optic: Rotating 40cm HOE, 1-m f.l.
• 45-deg off-nadir FOV
• Compact, folded optical path
• Coaxial laser transmission
• Active laser bore-sight
CLRC July 2007
Telescope Mechanical Design
3 mount points
Envelope Dimensions:
Total Mass: 51 kg (112 lb)
25” Height
30” Diameter (includes mounts and motor, 25” without)
CLRC July 2007
Laser Transmitter
Specifications
Performance Specifications/Design Performance Summary Table
Parameter
Specification
Design Performance
Margin
Wavelength
355 nm
355 nm
NA
Laser Energy (UV)
>30 mJ
40 mJ @ 1.3% duty cycle
> 33%
Pulse Rep Rate
200 Hz
200 Hz
NA
Average Power
>6W
8 W @ 1.3% duty cycle
> 33%
Beam Quality, M^2
<3
< 2.5
17%
Energy in the Bucket
> 86% encircled energy into 3x d. l. beam
Meet specification
TBD
Frequency Stability
< 5MHz RMS for 30 sec
< 50 MHz RMS for 30 min
Meet specification
< 30 MHz RMS for 30 min
TBD
40%
Seeding Efficiency
>99.9%
>99.9
Meets spec
Pulsewidth
> 15 ns
~13-15 ns
None
Linewidth
<120 MHz @ 355 nm
~120 MHz
None
Pointing stability
< 10% of beam divergence
< 10% of beam divergence
TBD
Electrical Power (excl. chiller)
550 W
470 W
14%
Thermal Management
Conductive or Liquid Cooled
Conductive to Liquid
NA
Lifetime
1 billion shots (75% diode derating) @ 1064 nm
1 billion shots @ 1064 nm
TBD
CLRC July 2007
Laser Module Overview





Injection seeded Nd:YAG ring oscillator with single amplifier
Frequency tripled to 355 nm
Pulse energy = 30 mJ @ 355 nm
Pulse Rep Frequency = 200 pps
Optical canister is 28cm x 33 cm
Front View
Resonance detection
photodiode
Ring oscillator
355 nm output
window
Amplifier Compartment
Oscillator
head
1064 & 532 nm
output window
Amplifier
Purge
port
Coolant
connector
Isolator
SHG
THG
Modulator & q-switch
drive electronics
Periscope
Seed
laser
Oscillator Compartment
See Hovis et al, “Advanced Transmitters for Ladar Applications” in Session 11
CLRC July 2007
TWiLiTE Assembly
4
3
2
5
1
1- Floor; 2- Mounting frame; 3- Optical
bench (laser &HOE rotating telescope);
4- Receiver & Electronics ; 5- WB57 Pallet
Mass: 250 kg
Power: 770W (not including heaters)
CLRC July 2007
Project Timeline
LASER
DELIVERY
JUL 2007
TELESCOPE
SUBSYS PDR
MAY 22, 2006
START:
AUG 2, 2005
SYSTEM REQ
WORKSHOP
DEC 1, 2005
PRELIM DES
REVIEW
JUL 20, 2006
FINISH:
AUG 1, 2008
2008
ETALON
DELIVERY
APR 2007
RECEIVER
DELIVERY
AUG 2007
TEST FLIGHTS
LATE SUMMER
2008
ASSEMBLY
INTEG & TEST
3Q/2007- 2Q/2008
2007
2006
RECEIVER
SUBSYS PDR
(GSFC IR&D)
MAR 2005
CRITICAL
DES REVIEW
MAY, 2007
CONCEPT
DES REVIEW
FEB 16, 2006
TELESCOPE
DELIVERY
AUG 2007
CLRC July 2007
TWiLiTE Summary
• TWiLiTE is a three year R&D project to design and build an
airborne scanning direct detection Doppler lidar
• The primary objective is to advance the TRL of key
component technologies as a stepping stone to space.
• The TWiLiTE Doppler lidar will be serve as a testbed to
validate critical technologies in a fully autonomous,
integrated Doppler lidar as a stepping stone to space.
• The instrument will is designed to measure full profiles of
winds from a high altitude aircraft and many of the design
elements may be transitioned to UAV or other suborbital
platforms for mesoscale and hurricane research.
Acknowledgements: ESTO IIP Program; Goddard Space Flight
Center IRAD program
CLRC July 2007
Backups
CLRC July 2007
Mission Applications
Global Tropospheric
Wind Sounder
• Improved NWP
• Hurricane and severe
storm prediction
Airborne Doppler Lidar
• Mesoscale research
• Improved hurricane prediction
• Satellite cal/val
• Technology validation
Exploration
•Martian winds
from orbit or surface
CLRC July 2007
Doppler Lidar Measurement Concept
MOLECULAR DOPPLER RECEIVER
• Molecular return gives lower
accuracy and resolution but signal is
always there
Double-edge filters sample wings of molecular
spectrum to measure Doppler shift
CLRC July 2007
Double Edge Doppler Lidar Heritage
Double-edge filters sample
wings of molecular spectrum
to measure Doppler shift
GLOW mobile Doppler lidar
• In 1999 the first
molecular “double edge”
Doppler receiver was
built as a proof of
principle experiment.
• The molecular receiver
was installed in the
GLOW mobile Doppler
lidar to demonstrate the
functionality and
scalability of the
approach
• 5 years of ground based
lidar wind measurements
in a wide variety of
conditions.
Receiver mounted in GLOW lidar
for field tests and measurements
m/s
deg
Time series of wind speed and
direction profiles from IHOP_2002
CLRC July 2007
TWiLiTE IIP Overview
Objective: Advance TRL of key enabling technologies for direct
detection Doppler lidar including validation at the instrument
system level from a high altitude aircraft
• NASA IIP 2004
HARLIE
Started: Aug 1, 2005
3 year effort
TWiLiTE
• Leverages significant technology
investments and instrument development
ESTO
heritage:
IPO
IR&D + SBIR + IPO + ESTO
•Laser – Fibertek
•Data System – Sigma
SBIR
GLOW
IR&D
•HOE – Ralcon
•FP etalon – MAC
• Heritage from Fielded Lidar Systems:
GLOW, CPL, HARLIE
CPL
CLRC July 2007
System Block Diagram
Power Dist/Sw
MOLECULAR DE DOPPLER RECEIVER
PRESSURE VESSEL
ETALON SPACING/PARALLELISM
ETALON
ANALOG/PHOTON COUNTS, SYS DATA
Bm Exp
SIGNAL FIBER
Data Acq.
SYNC
Timing/Control
AUTO TIP/TILT
ADJ
PRESSURE VESSEL
HOE Scanner/
Telescope
Laser
A/D SIGNAL
FIBER
WATER
POWER
INS/GPS
PRESSURE VESSEL
RECEIVER TEMP CONTROL
Etalon Control
Computer
AUTO
FOV TO
COMP
INS/GPS Data
Laser Cooling
Laser Power
Scanner Ctrl
Window
Det. Box Temp
PRESSURE VESSEL
CLRC July 2007
Rotating HOE Telescope
•
SIGNAL FIBER
•
AFT OPTICS
INS/GPS
•
Motor
Cmd & Data
Laser
Data
•
•
Data
Autoalignment
HOE
Window
Fine Steering
Mirror
Optical: laser, receiver,
window
Mechanical: optical
bench, window, autoalignment system (AAS)
Thermal: environmentwindow-HOE, thermal
system,
optical bench, payload
bay environment
Electrical: Data system,
power
Software: Command &
control, scan position,
boresight,
data
CLRC July 2007
TWiLiTE Predicted shot noise limited LOS error
2000 shot average, 250 m vertical resolution, background aerosol
CLRC July 2007