Doppler Lidar Scanning Telescope Technology Geary Schwemmer Meeting

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 Rotating Si. C 1. 25 m reflective telescope Scanning flat mirror Rotating Fresnel wedge Rotating 1. 5 -m HOE 1. 5 -m Sh. ADOE 302 kg Total Avg. Power 260 W >450 kg 152 kg 130 W 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 TRL 3 TRL 4 Wind Lidar Working Group, 29 June 2005 Welches, OR TRL 5

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

Baseline Scan Configuration 3 tracks, 6 lines of sight YA= 324 km 30° YB= 87 km 150° Satellite nadir ground track 324 km 90° YC= 237 km 0 12 237 km 33 57 78 90 seconds timing Z = 400 km, = 40°, A = 75°, B = 15°, C = 45° 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 distortion caused by HOE materials Wave-front corrective prescription applied to cover glass Wind Lidar Working Group, 29 June 2005 Welches, OR

Hybrid R-T Combination SHADOE Receiver (One FOV shown) UV Focal Plane UV Reflection SHADOE IR Transmission SHADOE IR Focal Plane Wind Lidar Working Group, 29 June 2005 Welches, OR