Wind Lidar Working Group, 29 June 2005 Welches, OR
Doppler Lidar Scanning Telescope Technology
Geary Schwemmer
Meeting of the Working Group on Space-based Lidar Winds
Welches, Oregon
June 28- July 1, 2005
Wind Lidar Working Group, 29 June 2005 Welches, OR
Topics
• Requirements
• Constraints
• Approaches
• Comparisons
• Roadmaps
Wind Lidar Working Group, 29 June 2005 Welches, OR
Requirements
• Narrow field of view
• Large collecting area
• Large off-nadir scan angles (~30-50°)
• Step-stare preferred over continuous scanning
• Rapid slew
• 2 ~orthogonal looks into each sample volume
• Laser bore-sighting
Wind Lidar Working Group, 29 June 2005 Welches, OR
Constraints
• Volume• Mass• Power• Vibration• Torque• Momentum compensation• Space environment
Wind Lidar Working Group, 29 June 2005 Welches, OR
Approaches
• Conventional telescope w/ rotating mount
• Multiple telescopes
• Scanning flat mirror
• Rotating wedge prism
• Rotating Fresnel prism
• Rotating HOE
• Multiplexed HOE / SHADOE
Wind Lidar Working Group, 29 June 2005 Welches, OR
Comparisons
Mass and Power comparisons. (Source - GSFC Doppler Lidar Technology assessment, 2001.)
System Total Mass Total Avg. Power
Rotating SiC 1.25 m reflective telescope
302 kg 260 W
Scanning flat mirror >450 kg
Rotating Fresnel wedge
>450 kg
Rotating 1.5-m HOE 152 kg 130 W
1.5-m ShADOE 65 kg 20 W
Wind Lidar Working Group, 29 June 2005 Welches, OR
Holographic Optics
IR
Wind Lidar Working Group, 29 June 2005 Welches, OR
Hybrid SHADOE Roadmap
TRL5TRL4
TRL3
Wind Lidar Working Group, 29 June 2005 Welches, OR
Key Remaining Issues
• Space qualification• 2-micron performance
(diffraction limited)• SHADOE demonstration• System trades:
– laser– # of FOVs & dwell time / spatial
resolution– hybrid configuration
• Scaling to 1 meter
Wind Lidar Working Group, 29 June 2005 Welches, OR
Conclusions
• Conventional scanning telescope too heavy• 2-micron & 355 nm requirements very
different (size & image quality), perhaps equally difficult
• HOE technologies offer significant weight and power savings for large apertures
• Perhaps the lowest TRL of UV Doppler components
• No show stoppers, but significant risk & development
Wind Lidar Working Group, 29 June 2005 Welches, OR
150°
Baseline Scan Configuration
Satellite nadir ground track
YA= 324 km
YB= 87 km
30°
Z = 400 km, = 40°, A = 75°, B = 15°, C = 45°
YC= 237 km 90°324 km
237 km
3 tracks, 6 lines of sight
0 90
seconds timing
12 7833 57
Wind Lidar Working Group, 29 June 2005 Welches, OR
Optical Layout(single HOE)
Wind Lidar Working Group, 29 June 2005 Welches, OR
UV-A exposure effects
Wind Lidar Working Group, 29 June 2005 Welches, OR
Wavefront Error Correction
Wave-front corrective
prescription applied to cover glass
Wave-front distortion caused by HOE materials
Wind Lidar Working Group, 29 June 2005 Welches, OR
Hybrid R-T Combination SHADOE Receiver(One FOV shown)
UV Reflection SHADOE
IR Transmission SHADOE
IR Focal Plane
UV Focal Plane
