TWiLiTE Tropospheric Wind Lidar Technology Experiment IIP Update B' Gentry1, G' Schwemmer6, M' McGil

1
TWiLiTE (Tropospheric Wind Lidar Technology
Experiment) IIP Update B. Gentry1, G.
Schwemmer6, M. McGill1, M. Hardesty2, A. Brewer2,
T. Wilkerson5, R. Atlas2, M.Sirota3, S.
Lindemann41NASA GSFC 2NOAA 3Sigma Space
Corp. 4Michigan Aerospace Corp. 5Space Dynamics
Lab 6SESI
Working Group on Space Based Lidar Winds January
17 - 19, 2006 Key West, FL
2
Outline

• TWiLiTE Overview
• Requirements and Error Budget
• WB57 Aircraft
• Instrument Development Status
• Summary

3
ESTOs Instrument Incubator Program
4
TWiLiTE Direct Detection Wind Lidar Key
Technologies
5
TWiLiTE Project Organization
Project Management PI Gentry PM, Sys Eng
Sirota, Chauvet, Mathur
Science Requirements and Applications Atlas,Gentry
, Hardesty, McGill, Brewer
Aircraft accomodations WB57- McGill, Chauvet GIV
Brewer, Hardesty
HOE Telescope/ Scanner POCSchwemmer Supplier
SDL
Laser POC Li Supplier TBD
Doppler Receiver GSFC POC Gentry Mech
Cooperider, Optics Bos IT Scott Thermal
Greer
System Integration/ Glue Sigma POC
Mathur
CDH Sigma POC Machan
FP Etalon MAC Lindemann
10 Ch MCS Sigma Machan
355 nm HOEs Wasach Photonics Ralison
6
Proposed TWiLiTE Measurement Requirements
Assumes scanner average angular velocity of 12
deg/sec
7
16 point step stare scan pattern
Top view

• Scanning parameters
• Constant dwell of 10s/LOS
• Scanner angular velocity of 12 deg/sec
• 192 sec to complete one cycle

Radial HLOS wind speed measured in a single range
bin for 3 cycles of the 16 point step stare scan
pattern. Assumes constant velocity (maximum 40
m/s)
8
(No Transcript)
9
Top level error budget (4 W laser)
Total LOS velocity accuracy 2.0 m/s
Photon shot noise 1.75 m/s
Doppler receiver spectral calib 0.35 m/s
Laser spectral 0.25 m/s
Margin 0.8 m/s
AC motion comp. 0.25 m/s
Total error 2.0 m/s 1.752 0.352 0.252
0.252 0.82
10
NASA Johnson WB57 Aircraft
11
WB57 Instrument Mounting
3 pallet
6 pallet
Looking forward from inside the payload bay
Pallet integration
12
Engine On
Take Off
Steep Ascent
Slow Ascent
Cruising
13
Three axis accelerometer data from WB57 at
operating altitude - Flight 2, 12/18/2005
14
IRAD Receiver Design Summary

• Volume reduced by 90 versus current GLOW
  receiver
• Optical path lengths minimized to improve
  mechanical, thermal stability
• End-to-end throughput increased by 60
• Signal dynamic range increased by 2 orders of
  magnitude

15
Michigan Aerospace TWiLiTE Etalon Design Features

• Discretely stepped plate creates three
  spectrally distinct resonant cavities
• Plate steps of 20.2 nm and 70.7 nm
• Plate reflectivity of 73 _at_ 355 nm
• Surface flatness of l/150 _at_ 633 nm
• Intragap capacitive feedback provides direct
  knowledge of gap dynamics
• Capacitors fabricated from Expansion Class 0
  Zerodur for minimal thermal contributions
• Stacked ring piezoelectric actuators provide gt 3
  microns dynamic range
• Closed loop operation provides sub-nanometer
  resolution of motion
• Invar construction provides thermal stability and
  mechanical robustness
• Vibration tests to confirm operation in aircraft
  environment scheduled in early February

16
Double Edge Etalon Channels
17
Michigan Aerospace TWiLiTE Etalon
Invar housing machined from solid piece ensures
material homogeneity, rigidity and minimizes
thermal deformation
Soft diaphragm mounting on actuated ring allows
for tuning with a minimal amount of
stress imparted to the ring/plate assembly while
holding the etalon rigidly centered on optical
axis.
3 point rigid mount at input creates stress free
reference plane and stable angle of incidence
18
TWiLiTE Holographic Telescope

• FUNCTIONS
• Collect and focus laser backscatter
• Scan laser and FOV
• Provide pointing knowledge to CDH
• FEATURES
• Primary Optic Rotating 40-cm HOE, 1-m f.l.
• 45-deg off-nadir FOV
• Compact, folded optical path
• Coaxial laser transmission
• Active laser bore-sight

19
TWiLiTE Telescope Team
Geary Schwemmer (SESI) lead POC Space Dynamics
Lab Team Thomas Wilkerson SDL lead
Brent Bos (GSFC) Optical
Engineering Jason Swasey Lead Engineer
Caner Cooperrider(GSFC) Mechanical
Eng. Jed Hancock Optical Engineering Brian
Thompson Mechanical Engineering Adam Shelley
Mechanical Engineering Marc Hammond
consultant Richard Rallison (Wasatch Photonics)
HOE consultant
20
TWiLiTE System Concept- As of Dec. 2005
TWiLiTE System Integrated on 3 foot pallet
Enclosure proposed to mitigate environmental
extremes
21
TWiLiTE Milestones
Project Start August, 2005
22
TWiLiTE Summary

• The TWiLiTE IIP is a three year RD project to
  design and build an airborne scanning direct
  detection Doppler lidar
• The primary objective is to advance the TRL of
  key component technologies as a stepping stone to
  space.
• At the end of the project we will have a fully
  autonomous, integrated Doppler lidar designed to
  measure full profiles of winds from a high
  altitude aircraft.
• We are actively seeking input on the instrument
  design requirements from the community. This
  includes input on potential applications, target
  field experiments, etc for the TWiLiTE
  instrument.

23

• Backups

24
Doppler Lidar Measurement Concept

• DOPPLER RECEIVER - Multiple flavors dependent
  on scattering target -
• Aerosol return gives high accuracy and high
  spatial and temporal resolution when aerosols
  present
• Molecular return gives lower accuracy and
  resolution but signal is always there

25

• High altitude airborne direct detection scanning
  Doppler lidar
• Serves as a system level demonstration and as a
  technology testbed
• Leverages technology investment from multiple
  SBIRs, ESTO, IPO and internal funding
• Consistent with the roadmap and planning
  activities for direct detection and hybrid
  Doppler lidar implementations

26
(No Transcript)
27
(No Transcript)
28
Photon shot noise v err 1.75 m/s
Optical throughput (Mean value and vs
polarization,T,P and grms)
Laser
HOE collecting area
Boresight and alignment

• Laser
• Far field diverg
• Pointing jitter
• FOV
• fiber diam
• HOE fl
• HOE
• Spot size
• Rotational/optical axis alignment
• Bearing TIR
• HOE/laser mechanical mounting
• Active alignment mechanism

• Energy
• (mean, jitter and drift)
• PRF
• Seeding efficiency
• Spectral purity

• Transmit optics
• HOE receiver
• Diffraction eff
• Transmission
• Doppler receiver
• End to end trans per edge channel
• PMT QE
• Etalon transmission
• Fiber optic
• coupling
• attenuation
• bulkhead feedthru

Spatial and temporal Averaging
29
Doppler receiver v err 0.35 m/s
Etalon spectral (Mean value and vs
polarization,T,P and grms)
PMT
Optical constants
Atmospheric effects (vs altitude)

• Temperature
• Density (Rayleigh Brillouin lineshape)
• Backscatter ratio
• Clouds

• QE
• Response linearity
• Dynamic range

• Instrument function (total response measured in
  calibration)
• Etalon finesse
• Plate flatness
• Angluar broadening (pinhole finesse)
• Gap (FSR)
• Plate parallelism
• Edge channel separation

• Intensity split ratio of edge channels

30
Laser spectral 0.25 m/s
Laser linewidth at 355 nm
Laser reference measurement

• Laser frequency stabilty (jitter and drift) over
  measurement interval

• Etalon locking channel finesse and transmission
• analog PMT response
• analog sampling and detection (boxcar)
• number of shots averaged per ref meas

31
A/C motion compensation 0.25 m/s

• Knowledge of Aircraft ground speed and direction
  

• Transceiver pointing angle measured in
  instrument reference frame

Coarse Doppler compensation offset (receiver or
laser) if used

• Aircraft orientation (Pitch, roll, yaw) measured
  in instrument reference frame by POS

32
TWiLiTE Schedule

• August 2005 start
• Initial Test Flights in 2008