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CLRC July 2007
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 WindsJuly 17-20, 2007Snowmass, CO
CLRC July 2007
Outline
• TWiLiTE Overview• Requirements and Performance Simulations• Instrument Subsystem Status• Summary
CLRC July 2007
Technology Maturity Roadmap
2 micron laser 1988
Demo UAV OperationAircraft
Operation
Compact Packaging 2005
Space Qualif.
Pre-Launch Validation
Packaged Lidar Ground Demo. 2007
Conductive Cooling Techn. 1999
Operational
Autonomous Oper. Technol.2008 (Direct)
Space Qualif.
Pre-Launch Validation
2-Micron Coherent Doppler LidarLaser Risk Reduction Program
IIP-2004 Projects
Past Funding
Diode Pump Technology 1993
Inj. Seeding Technology 1996
Autonomous Oper. Technol.
1 micron laser
Compact Laser Packaging 2007
Compact Molecular Doppler Receiver 2007
Conductive Cooling Techn.
Diode Pump Technology
Inj. Seeding Technology
High Energy Technology 1997
High Energy Laser Technology
Lifetime Validation
Lifetime Validation
0.355-Micron Direct Doppler Lidar
TWiLiTE
CLRC July 2007
• 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 for autonomous operation on the NASA WB57.
• TWiLiTE will be completed in summer 2008.
• The instrument could be transitioned to a UAV like Global Hawk .
Tropospheric Wind Lidar Technology Experiment (TWiLiTE) Instrument Incubator Program
UV Laser
Rotating HOE telescope
Doppler Receiver
TWiLiTE system integrated on WB57 3 foot pallet
CLRC July 2007
Airborne Doppler Lidar Wind Profiling
Lidar ranging permits determination of wind speed as a function of altitude.Multiple look angles permit determination of vector wind.
250 m
CLRC July 2007
TWiLiTE Target Platform
Modular palletNadir view
Payload mounting
110V, 4 X 25A, 3 phase, 400 Hz; 28V DC 35A
Payload Electrical Power
374 kg per pallet X 4 pallets.
Payload mass
200 m/s @ 18 kmCruise Speed
6.5 hoursDuration
18 kmMax. Altitude
WB57Specification
WB57 Aircraft: NASA Johnson Space Center
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
Wavelength 354.7 nmTelescope/Scanner Area 0.08 m2
Laser Linewidth (FWHH) 150 MHzLaser Energy/Pulse (6 W) 30 mJ @ 200 pps
(8 W) 40 mJ @ 200 ppsEtalon FSR 16.65 GHzEtalon FWHH 2.84 GHzEdge Channel Separation 6.64 GHzLocking Channel Separation 4.74 GHzInterference filter BW (FWHH) 120 pmPMT Quantum Efficiency 25%Optical Efficiency (Edge w/o BS or etalon) 0.37BS 0.41
TWiLiTE Instrument Parameters
CLRC July 2007
0 5 15 2010Altitude (km)
det
ecte
d p
hot
ons
104
105
106
107
black = overlap corrected, no max. count rateblue = overlap corrected, 50 MHz max. count rate
Photocounts Detected in each Edge Channel10 sec (2000 shot) integration; z=250 m; 45 deg nadir
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
red = performance with current system parameters
blue = performance with expected system parametersA
ltit
ud
e (k
m)
L-O-S wind error (m/s)
Simulated L-O-S wind error
0
5
15
20
10
0.0 0.5 1.0 1.5 2.0
Current system performance (red curve) includes telescope with 58% diffraction efficiency and 55% encircled energy.
Expected system performance (blue curve) includes telescope with 62% diffraction efficiency and 82% encircled energy.
In both cases, the black curve is the performance with no solar background included.
TWILITE system performance
CLRC July 2007
8 point conical step stare scan pattern
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)
Aircraft motion
CLRC July 2007
Entrance TRL
Exit TRL
• High spectral resolution all solid state laser transmitter
4 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 Optical Element telescopes and scanning optics
3 5-6
TWiLiTE Direct Detection Wind Lidar Key Technologies
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 40-
cm 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
Envelope Dimensions:25” Height30” Diameter (includes mounts and motor, 25” without)
Total Mass: 51 kg (112 lb)
3 mount points
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 > 6 W 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
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
Amplifier Compartment
Oscillator Compartment
Modulator & q-switch drive electronics
Ring oscillator
Amplifier
Resonance detection photodiode
Seed laser
THG
SHG
Laser Module Overview
Oscillator head
Isolator
Periscope
Front View
Coolant connector
Purge port
355 nm output window
1064 & 532 nm output window
See Hovis et al, “Advanced Transmitters for Ladar Applications” in Session 11
CLRC July 2007
TWiLiTE Assembly
1- Floor; 2- Mounting frame; 3- Optical bench (laser &HOE rotating telescope); 4- Receiver & Electronics ; 5- WB57 Pallet
1
2
3
4
5
Mass: 250 kgPower: 770W (not including heaters)
CLRC July 2007
Project Timeline
START:
AUG 2, 2005
SYSTEM REQ
WORKSHOP
DEC 1, 2005
CONCEPT
DES REVIEW
FEB 16, 2006
20
06
20
07
20
08
CRITICAL
DES REVIEW
MAY, 2007
TEST FLIGHTS
LATE SUMMER
2008
FINISH:
AUG 1, 2008
TELESCOPE
SUBSYS PDR
MAY 22, 2006
PRELIM DES
REVIEW
JUL 20, 2006
ETALON
DELIVERY
APR 2007
RECEIVER
DELIVERY
AUG 2007
LASER
DELIVERY
JUL 2007
RECEIVER
SUBSYS PDR
(GSFC IR&D)
MAR 2005
TELESCOPE
DELIVERY
AUG 2007
ASSEMBLY
INTEG & TEST
3Q/2007- 2Q/2008
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
• 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.
-0.5
0
0.5
1
1.5
2
2.5
3
-6 -4 -2 0 2 4 6
Lidar Signal vs. Etalon Transmision
Frequency (GHz)
Edge2 Filter
Locking Filter
Edge1 Filter
Aerosol Spectrum
Rayleigh Spectrum
m/s
deg
Double-edge filters sample wings of molecular spectrum to measure Doppler shift
GLOW mobile Doppler lidar
Receiver mounted in GLOW lidar for field tests and measurements
Time series of wind speed and direction profiles from IHOP_2002
CLRC July 2007
TWiLiTE IIP Overview
IPO
ESTO
SBIR
HARLIE
GLOW
CPL
TWiLiTE
• NASA IIP 2004
Started: Aug 1, 2005
3 year effort
• Leverages significant technology
investments and instrument
development heritage:
IR&D + SBIR + IPO + ESTO
•Laser – Fibertek
•Data System – Sigma
•HOE – Ralcon
•FP etalon – MAC
• Heritage from Fielded Lidar Systems:
GLOW, CPL, HARLIE
IR&D
Objective: Advance TRL of key enabling technologies for direct detection Doppler lidar including validation at the instrument system level from a high altitude aircraft
CLRC July 2007
System Block Diagram
Scanner Ctrl
Laser Power
Timing/Control
Data Acq.
Laser
Com
puter
HOE Scanner/Telescope
Laser Cooling
SIGNAL FIBER
ANALOG/PHOTON COUNTS, SYS DATA
Etalon Control
SYNCAUTOFOV TO COMP
Det. Box Temp
PRESSURE VESSEL
ETALON
Bm Exp
RE
CE
IVE
R T
EM
P C
ON
TR
OL
ETALON SPACING/PARALLELISM
A/D SIGNALFIBERWATERPOWER
AUTO TIP/TILT ADJ
INS/GPS Data
Power Dist/Sw
INS
/GP
S
MOLECULAR DE DOPPLER RECEIVER
PRESSURE VESSEL
PRESSURE VESSEL
PRESSURE VESSEL Window
CLRC July 2007
Rotating HOE Telescope
• Optical: laser, receiver, window
• Mechanical: optical bench, window, auto-alignment system (AAS)
• Thermal: environment-window-HOE, thermal system,
optical bench, payload bay environment
• Electrical: Data system, power
• Software: Command & control, scan position, boresight,
data
Laser
SIGNAL FIBER
AFT OPTICS
INS
/GP
S
Window
HOE
Mot
or
Cmd & Data
Data
Data
Fine Steering Mirror
Auto-alignment
CLRC July 2007
TWiLiTE Predicted shot noise limited LOS error2000 shot average, 250 m vertical resolution, background aerosol