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