slwg feb 2007 progress on the twilite direct detection doppler lidar instrument incubator program b....
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SLWG Feb 2007
Progress on the TWiLITE Direct Detection Doppler Lidar Instrument Incubator Program
B. Gentry1, G. Schwemmer6, M. McGill1, M. Hardesty2, A. Brewer2, T. Wilkerson5, R. Atlas2, M.Sirota3, S. Lindemann4
1NASA GSFC; 2NOAA; 3Sigma Space Corp.; 4Michigan Aerospace Corp.; 5Space Dynamics Lab; 6SESI
Lidar Working Group on Space Based Lidar WindsFebruary 6-9, 2007
Miami, FL
SLWG Feb 2007
• High altitude airborne molecular direct detection scanning Doppler lidar
• Serves as a system level demonstration of key technologies and subsystems
• Leverages significant technology investment from multiple sources
• On development path for future space based direct detection and ‘hybrid’ Doppler lidar implementations
TWiLiTE Instrument Incubator Program (IIP)
SLWG Feb 2007
TWiLiTE Measurement Requirements
Parameter WB57
Velocity accuracy (HLOS projected) (m/s) 2.0
Range of regard (km) 0 to18
Vertical resolution (km) 0.25
Horizontal resolution (km) (scan pattern 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
* Assumes scanner average angular velocity of 12 deg/sec
SLWG Feb 2007
Wavelength 354.7 nmTelescope/Scanner Area 0.08 m2
Laser Linewidth (FWHH) 150 MHzLaser Energy/Pulse (6 W @ 355nm) 30 mJ @ 200 ppsEtalon FSR 16.65 GHzInterference filter BW (FWHH) 120 pmPMT Quantum Efficiency 25%
TWiLiTE Instrument Parameters
SLWG Feb 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.
SLWG Feb 2007
0 5 15 2010Altitude (km)
0.0
0.5
1.0
1.5
2.0
L-O
-S w
ind
err
or (
m/s
)
black = no solar backgroundblue = 50 MHz max. count rate, with solar background
Simulated Shot noise limited L-O-S wind error10 sec (2000 shot) integration; z=250 m; 45 deg nadir
Presence of solar background is only apparent at low altitudes due to the laserenergy and small effective passband of the interference filter and etalon.
SLWG Feb 2007
Specification WB57
Max. Altitude 18 km
Duration 6.5 hours
Cruise Speed 210 m/s @ 18 km
Payload mass 1814 kg (incl. pallets)
Payload Electrical Power
4 X 25 A , 3 phase, 400 Hz
Payload mounting Modular palletNadir view
Window diameter; viewing orientation
45 cm; nadir view
NASA Johnson WB57 Aircraft
3’ palletPallet integration
SLWG Feb 2007
TWiLiTE Direct Detection Wind Lidar Key Technologies
• High spectral resolution all solid state laser transmitter
• High spectral resolution optical filters
• Efficient 355 nm photon counting molecular Doppler receiver technologies • Novel UV Holographic Optical Element telescopes and scanning optics
SLWG Feb 2007
-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
Double Edge Etalon Channels
SLWG Feb 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
SLWG Feb 2007
Receiver Mechanical Assembly
Overall Dimensions (LxWxH) : 0.468m x 0.446m x 0.30m
• Fiber coupled input from HOE telescope• High QE (>25%) low noise PMT’s used in photon counting mode. • Multiple PMT’s per channel to increase dynamic range.• Environmentally controlled (T, P vib) for high altitude aircraft operation.
SLWG Feb 2007
TWiLiTE HOE Telescope Design
HOE
Designed and built by Utah State Univ./SDL 355 nm HOE fabricated by Wasatch Photonics Mass 43 kg Power 35 W Volume 60 cm diameter x 60 cm long ~Isothermal environment, active control
SLWG Feb 2007
Laser Optics Module
Fibertek Laser Design Full Assembly
• Dual compartment design with oscillator and amplifier on opposite sides
• Hermetic sealing for low pressure operation
• An ~ 31 cm x 25 cm x 14 cm canister will accommodate the required modules
• Design is derived from one being developed for a NASA Langley High Spectral Resolution Lidar system
SLWG Feb 2007
TWiLiTE Subsystems
Laser
HOE telescope
Receiver
Electronics
SLWG Feb 2007
TWiLiTE Integrated on WB57 Pallet
SLWG Feb 2007
Project Milestones
START:
AUG 2, 2005
SYSTEM REQ
WORKSHOP
DEC 1, 2005
CONCEPT
DES REVIEW
FEB 16, 2006
2006
2007
2008
CRITICAL
DES REVIEW
MAR, 2007
ASSEMBLY
INTEG & TEST
3Q/2007- 2Q/2008
TEST FLIGHTS
LATE SUMMER
2008
FINISH:
AUG 1, 2008
TELESCOPE
SUBSYS PDR
MAY 22, 2006
PRELIM DES
REVIEW
JUL 20, 2006
ETALON
DELIVERY
APRIL 2006
RECEIVER
DELIVERY
MAR 2006
LASER
DELIVERY
JUN 2007
RECEIVER
SUBSYS PDR
(GSFC IRAD)
MAR 2005
TELESCOPE
DELIVERY
AUG 2007
SLWG Feb 2007
TWiLiTE Summary
• TWiLiTE is a three year R&D project to design and build an airborne scanning direct detection Doppler lidar
• 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 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: NASA ESTO IIP Program; Goddard Space Flight Center IRAD program
SLWG Feb 2007
8 point conical step stare scan pattern
Top view
Scanning parameters:
• Constant dwell of 10s/LOS
• Fixed azimuth increments of 45 deg 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)
0 10 20 30 40 50 60-40
-30
-20
-10
0
10
20
30
40
Distance (km)
Veloctiy (m/s)
Aircraft motion
SLWG Feb 2007
• Focal Length 993 2mm• Diffraction Angle 45.26 0.5 deg.• Diffraction Efficiency 64 2%• 160-200µm 1/e2 focal spots
Holographic Optical Element