Lidar winds from GEO: The Photons to Winds Conversion Efficiency Ball Aerospace & Technologies Corp. Lidar winds from GEO: The Photons to Winds Conversion Efficiency Christian J. Grund, and Jim Eraker Ball Aerospace & Technologies Corp. (BATC), cgrund@ball.com, 303-939-7217 Dave Emmitt Simpson Weather Associates, demmitt@swa.com, Bruce Gentry Goddard Space Flight Center, bruce.gentry@nasa.gov Aug. 4, 2011, Boulder, CO Response to questions raised at the Working Group on Space-based Lidar Winds in Bar Harbor, ME August 24, 2010 Agility to Innovate, Strength to Deliver

Review: GEOWindSat Hardware Components – Confluence of Multiple Recent Technology Developments Electrically Steerable Flash Lidar (ESFL) – Subject of Carl Weimer’s current NASA ESTO IIP (1J/pulse OK, >100X100 independent beamlets OK) 532nm, 0.5 – 1J/pulse, 100 Hz (current tech) Independently retargetable beams No momentum compensation Electronic Beam forming and steering AOM Laser Subject of Ball IRAD development and current NASA ESTO IIP demonstration (3D Winds focus) Patent pending Patents pending 4-phase Field-widened OAWL Receiver Fixed-pointing Wide-Field Receiver Telescope (~3°X3°) Subject of Ball IRAD development for high-sensitivity and resolution flash lidar and low- light passive astrophysical imaging (Intensified Imaging Photon Counting (I2PC) FPA). New. Top level hypothetical architecture block diagram, no data 4 Photon counting Profiling, Flash Lidar Imaging Arrays Co-boresighted camera to geo-locate pixels from topographic outlines Patent pending ESFL allows targeting with high spatial resolution and adaptive cloud avoidance Ball Aerospace & Technologies

Review: GEOWindSat Observatory predicted horizontal wind precision (satellite at -45° lon) Accessible Region 73° S Mature model. Assumptions: 16 simultaneous pixels, 20 minute integration at 3 km altitude in daylight. See presentation from Feb. 2010 he last working group meeting in Destin, FL

GLO vs. Geo-OAWL: Salient Features GLO GeoWindSat 1.5 Laser Energy (J) 1.0 100 Laser PRR (Hz) 100 355 Wavelength (nm) 532 Molecules Backscatter Targets Aerosols 100 Telescope Diam. (m) 2 5 Dwell Time/Beam (s) 1200 1 Simultaneous Beams 16 Opto-mech. Beam Steering Electronic Telescope Aperture (to scale) Unlikely (mass/vol.) Feasible within SoA (even a demo on a hosted payload on com satellite is feasible with 1 steerable beam and 1/2m telescope) How is this possible?

Areas for System Comparison Photon Transmitter Laser- energy, rep rate, pulse width, wavelength Optics- throughput, beam diameter, beam pointing signal Geometry- range, angle thru atmosphere, altitude resolution Backscatter- scatterer type, backscatter cross section Extinction- integrated aerosol and molecular, clouds Background light- solar/view angles, scattering optics, attenuation Turbulence- refractive and kenetic (spectral) Phenomenology Optical noise Photon Receiver Geometry- collection area, FOV Optical- throughput, bandwidth Key to discrepancies Converter Detector Spectral Analyzer Signal Processor Efficiency- Photons in / wind precision out (inc. analyzer algorithm leverage and detection noise) Resolution-Temporal, spatial Performance

Initial Comparison Assumptions Parameter GLO (DD etalon) GEOWindSat (OAWL) Dawn-like (Coherent) CALIPSO (DD) Wavelength nm 355 532 2150 Pulse energy J 1.5 1 0.5 0.11 Rep rate Hz 100 10 20 Pulse bandwidth MHz 25 1.6 multimode Transmit x Assume0.9 0.9 Assume 0.8 Photons out / s *1019 32 24 4.3 0.53 Range Mm 38 0.7 (LEO) Altitude for comparison km 3 Altitude Res km 0.250 0.0075 Look angle deg LOS Scatterer type molecules aerosols Aerosols and molecules Optical depth 0.3 0.05 NA Background W/nm/sr Turbulence refractive Background photons / s Turbulence spectral Telescope diameter m 2 0.15 Receive x 0.016 0.31 FOV mrad ? 30 5 130 Optical Bandwidth pm 10?? 10e-4 (10 MHz (search)) 37 Analyzer Photon x / 1m/s 2.52e6 1300 Time resolution s 1200 0.1 No data just hyperbole

Baseline from CALIPSO radiometric modeling assumed for Comparison Radiometric Backscatter and Extinction Assumptions (this is a ratio in the comparison so relative results do not depend strongly on exact model) Baseline from CALIPSO radiometric modeling assumed for Comparison GEOWindSat GLO Transmission to 3 km altitude: 355nm 0.4 532nm 0.8

1st Order Radiometric Analysis and Result 1.3 2.2 129 5.2*10-4 6.4*10-2 Advantage GLO Advantage GEOWindSat Net Single Beam Advantage to GEOWindSat (but comparable performance)

Symbols Phot_trans transmitted photons/pulse Phenom effect of atmospheric backscatter and transmission Phot_rec photon collection scaling factor Conv conversion efficiency from photons to LOS speed xtrans transmitter optical efficiency E0 pulse energy bp volume backscatter cross section R Range xrec receiver optical efficiency Ar area of the receiver DR range averaging bin in measurement T 1-way atmospheric transmission PRR pulse repetition rate Tavg independent measurement averaging time xphot-to-V number of photons at the detector needed for 1 m/s precision c speed of light h Planck’s constant

Conclusion Radiometric controversy resolved by this note GEOWindSat and GLO have comparable performance even though the telescope size is vastly different The main factors are photon to velocity conversion efficiency and Averaging CONOPS GLO assumes an etalon discriminator using Doppler broadened molecular backscatter and the optical throughput of an etalon filter GEOWindSat uses narrow bandwidth aerosol backscatter and the high throughput OA interferometer GLO measures for a short time and moves on GEOWindSat dwells for 20 min and may use multiple electronically targetable fov’s Radiometric controversy resolved by this note Other issues for another time: refractive index effects on measurement altitude and position daytime background light conops and meteorological relevance An OAWL at 1 mm with newer detectors might be a good trade

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GEOWinds Observatory predicted horizontal wind precision (satellite at -45° lon) Accessible Region 73° S Mature model. Assumptions: 16 simultaneous pixels, 20 minute integration at 3 km altitude in daylight.

Observatory Performance over Field of Regard 21 range bins/profile are assumed producing the indicated altitude resolution.

What if we put all the laser power in a sequentially addressed single pixel ? Observatory: ~20 profiles in 20 minutes, but not simultaneous

GEO Hosted payload horizontal wind precision Assumption: for a single pixel, 20 minute integration at 3 km altitude in daylight

The GEOWinds Hosted Payload horizontal wind velocity precision in the FOR The hosted payload approach fits within the Venture Class small sat envelope and would generate useful science data while demonstrating and validating observatory capabilities (at a reduced temporal resolution)

GEOWindSat Hosted Payload Conceptual Configuration Front View Top View Telescope Solar Filter Aft View Camera Housing Side View Interferometer Housing Telescope Aft Metering Structure

Modeled GEOWindSat Hosted Payload SWaP Available on communications satellites <1000 <2 <460

Potential Optical Refraction Effects on Altitude Assignment Uncertainties Beam height refractive deflection for typical cell in FOR and 87o from local nadir.