Jan 2006

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. Lindemann4

1NASA GSFC; 2NOAA; 3Sigma Space Corp.; 4Michigan Aerospace Corp.; 5Space Dynamics Lab; 6SESI

Working Group on Space Based Lidar WindsJanuary 17 - 19, 2006

Key West, FL

Jan 2006

Outline

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

Jan 2006

ESTO’s Instrument Incubator Program

Jan 2006

Entrance TRL

Exit TRL

• High spectral resolution all solid state laser transmitter

4 5-6

• High spectral resolution optical filters

4 5-6

• Efficient 355 nm photon counting molecular Doppler receiver technologies

4 5-6

• Novel UV Holographic Optical Element telescopes and scanning optics

3 5-6

TWiLiTE Direct Detection Wind Lidar Key Technologies

Jan 2006

Project ManagementPI – Gentry

PM, Sys Eng – Sirota, Chauvet, Mathur

Science Requirements and Applications

Atlas,Gentry, Hardesty, McGill, Brewer…

HOE Telescope/

Scanner

POC:Schwemmer

Supplier: SDL

Laser

POC: Li

Supplier: TBD

Doppler Receiver

GSFCPOC: GentryMech: Cooperider,Optics: BosI&T : ScottThermal: Greer

System Integration/

‘Glue’ Sigma POC: Mathur

C&DH

Sigma

POC: Machan

FP EtalonMAC

Lindemann

10 Ch MCS+ SigmaMachan

355 nm HOE’sWasach

PhotonicsRalison

Aircraft accomodationsWB57- McGill, ChauvetGIV – Brewer, Hardesty

TWiLiTE Project Organization

Jan 2006

Proposed TWiLiTE Measurement Requirements

Parameter WB57

Velocity accuracy (HLOS projected) (m/s) 2.0

Range of regard (km) 0-18

Vertical resolution (km) 0.25

Horizontal resolution (km) 25

Groundspeed (m/s) 200

Nadir angle (deg) 45

Scan pattern Up to 16 pt step-stare

Horizontal integration per LOS (seconds)//ground track (km)

10//2

* Assumes scanner average angular velocity of 12 deg/sec

Jan 2006

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

0 100 200 300 400 500 600-40

-30

-20

-10

0

10

20

30

40

Time (s)

Veloctiy (m/s)

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)

Jan 2006

Jan 2006

Top level error budget (4 W laser)

Total LOS velocity accuracy2.0 m/s

Photon shot noise1.75 m/s

Doppler receiver spectral calib

0.35 m/s

Laser spectral0.25 m/s

Margin0.8 m/s

Total error =2.0 m/s = 1.752 + 0.352 + 0.252 + 0.252 + 0.82

AC motion comp.0.25 m/s

Jan 2006

Specification WB57

Max. Altitude 18 km

Duration 6.5 hours

Cruise Speed 210 m/s @ 18 km

Payload mass 1814 kg (incl. pallets)

Payload Electrical Power

4 X 25 A , 3 phase, 400 Hz

Payload mounting Modular palletNadir view

Window diameter; viewing orientation

45 cm; nadir view

NASA Johnson WB57 Aircraft

Jan 2006

3’ pallet 6’ pallet

Looking forward from inside the payload bay

WB57 Instrument Mounting

Pallet integration

Jan 2006

Engine On

TakeOff

Steep Ascent

SlowAscent

Cruising

Jan 2006

0 500 1000 1500 2000 250010

-5

10-4

10-3

10-2

10-1

100

101

102

103 Cruising

g2 /H

z

Hz

XYZ

Three axis accelerometer data from WB57 at operating altitude - Flight 2, 12/18/2005

Jan 2006

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

Jan 2006

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% @ 355 nm• Surface flatness of /150 @ 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 > 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

Jan 2006

-0.5

0

0.5

1

1.5

2

2.5

3

-6 -4 -2 0 2 4 6

Lidar Signal vs. Etalon Transmision

Frequency (GHz)

Edge2 Filter

Locking Filter

Edge1 Filter

Aerosol Spectrum

Rayleigh Spectrum

Double Edge Etalon Channels

Jan 2006

3 point rigid mount at input creates stress free reference planeand stable angle of incidence

‘Soft’ diaphragm mounting on actuated ringallows for tuning with a minimal amount of stressimparted to the ring/plate assembly while holding the etalonrigidly centered on optical axis.

Invar housing machined from solid pieceensures material homogeneity, rigidity and minimizes thermal deformation

Michigan Aerospace TWiLiTE Etalon

Jan 2006

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

Jan 2006

TWiLiTE Telescope TeamGeary Schwemmer (SESI) – lead POCSpace Dynamics Lab TeamThomas Wilkerson – SDL lead Brent Bos (GSFC) –Optical EngineeringJason Swasey – Lead Engineer Caner Cooperrider(GSFC) Mechanical Eng.Jed Hancock – Optical EngineeringBrian Thompson – Mechanical EngineeringAdam Shelley – Mechanical EngineeringMarc Hammond – consultantRichard Rallison (Wasatch Photonics) – HOE consultant

Jan 2006

TWiLiTE System Concept- As of Dec. 2005

TWiLiTE System Integrated on3 foot pallet

Enclosure proposed to mitigate environmental extremes

Jan 2006

TWiLiTE MilestonesMilestone Months after task start*

System Definition Review 5 mos

Fabry-Perot etalon optical head delivered 6 mos

Preliminary Design Review 8 mos

Doppler Receiver delivered 8 mos

Digital etalon controller delivered 14 mos

Critical Design Review 14 mos

Laser and electronics delivered 22 mos

HOE Telescope/scanner delivered 24 mos

Data acquisiton and control electronics delivered 24 mos

Phase 2 Annual Review 24 mos

Instrument pallet and support equipment delivered 26 mos

Flight instrument integration and ground testing 28 mos

Flight Readiness Review 28 mos

Initial TWiLiTE flight test 34 mos

Project complete / Final Report 36 mos

*Project Start August, 2005

Jan 2006

TWiLiTE Summary

• The TWiLiTE IIP is a three year R&D 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.

Jan 2006

Backups

Jan 2006

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

Molecular ()

Aerosol ()

Backscattered Spectrum

Frequency

DOP

Jan 2006

• 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

Jan 2006

Jan 2006

Jan 2006

Photon shot noise v err1.75 m/s

Optical throughput(Mean value and vs

polarization,T,P and grms)

Spatial and

temporal Averaging

Boresight and alignment

Transmit opticsHOE receiver

• Diffraction eff• Transmission

Doppler receiver • End to end trans per edge channel• PMT QE• Etalon transmission

• Fiber optic• coupling• attenuation• bulkhead feedthru

Laser

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

HOE collecting

area

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

Jan 2006

Doppler receiver v err0.35 m/s

Etalon spectral (Mean value and vs

polarization,T,P and grms)

Atmospheric effects (vs altitude)

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

PMT

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

Optical constants

• QE• Response linearity• Dynamic range

• Intensity split ratio of edge channels

Jan 2006

Laser spectral 0.25 m/s

Laser linewidth at 355 nm • Laser frequency stabilty (jitter and drift) over measurement interval

Laser reference measurement

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

Jan 2006

A/C motion compensation 0.25 m/s

• Knowledge of Aircraft ground speed and direction

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

• Transceiver pointing angle measured in instrument reference frame

Coarse Doppler compensation offset (receiver or laser) if used

Jan 2006

TWiLiTE Schedule• August 2005 start• Initial Test Flights in 2008