SLWG Feb 2007 Progress on the TWiLITE Direct Detection Doppler Lidar Instrument Incubator Program B. Gentry 1, G. Schwemmer 6, M. McGill 1, M. Hardesty 2, A. Brewer 2, T. Wilkerson 5, R. Atlas 2, M.Sirota 3, S. Lindemann 4 1 NASA GSFC; 2 NOAA; 3 Sigma Space Corp.; 4 Michigan Aerospace Corp.; 5 Space Dynamics Lab; 6 SESI Lidar Working Group on Space Based Lidar Winds February 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 ParameterWB57 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 patternUp 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 Wavelength354.7 nm Telescope/Scanner Area0.08 m 2 Laser Linewidth (FWHH)150 MHz Laser Energy/Pulse (6 355nm) pps Etalon FSR GHz Interference filter BW (FWHH)120 pm PMT Quantum Efficiency25% TWiLiTE Instrument Parameters

SLWG Feb Altitude (km) detected photons black = overlap corrected, no max. count rate blue = overlap corrected, 50 MHz max. count rate Photocounts Detected in each Edge Channel 10 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 Altitude (km) L-O-S wind error (m/s) black = no solar background blue = 50 MHz max. count rate, with solar background Simulated Shot noise limited L-O-S wind error 10 sec (2000 shot) integration;  z=250 m; 45 deg nadir Presence of solar background is only apparent at low altitudes due to the laser energy and small effective passband of the interference filter and etalon.

SLWG Feb 2007 SpecificationWB57 Max. Altitude18 km Duration6.5 hours Cruise Speed km Payload mass1814 kg (incl. pallets) Payload Electrical Power 4 X 25 A, 3 phase, 400 Hz Payload mountingModular pallet Nadir view Window diameter; viewing orientation 45 cm; nadir view NASA Johnson WB57 Aircraft 3’ pallet Pallet 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 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, CRITICAL DES REVIEW MAR, 2007 ASSEMBLY INTEG & TEST 3Q/ Q/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 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) Aircraft motion

SLWG Feb 2007 Focal Length 993  2mm Diffraction Angle  0.5 deg. Diffraction Efficiency 64  2% µm 1/e2 focal spots Holographic Optical Element