CLRC July 2007

Mid-term status of the TWiLiTE direct detection Doppler lidar development program

Bruce Gentry1, M. McGill1, G. Schwemmer6, M. Hardesty2, A. Brewer2, T. Wilkerson5, R. Atlas2, M.Sirota3, S. Lindemann4, F.

Hovis7

1NASA GSFC; 2NOAA; 3Sigma Space Corp.; 4Michigan Aerospace Corp.; 5Space Dynamics Lab; 6SESI, 7Fibertek Inc

Working Group on Space-Based Lidar WindsJuly 17-20, 2007Snowmass, CO

CLRC July 2007

Outline

• TWiLiTE Overview• Requirements and Performance Simulations• Instrument Subsystem Status• Summary

CLRC July 2007

Technology Maturity Roadmap

2 micron laser 1988

Demo UAV OperationAircraft

Operation

Compact Packaging 2005

Space Qualif.

Pre-Launch Validation

Packaged Lidar Ground Demo. 2007

Conductive Cooling Techn. 1999

Operational

Autonomous Oper. Technol.2008 (Direct)

Space Qualif.

Pre-Launch Validation

2-Micron Coherent Doppler LidarLaser Risk Reduction Program

IIP-2004 Projects

Past Funding

Diode Pump Technology 1993

Inj. Seeding Technology 1996

Autonomous Oper. Technol.

1 micron laser

Compact Laser Packaging 2007

Compact Molecular Doppler Receiver 2007

Conductive Cooling Techn.

Diode Pump Technology

Inj. Seeding Technology

High Energy Technology 1997

High Energy Laser Technology

Lifetime Validation

Lifetime Validation

0.355-Micron Direct Doppler Lidar

TWiLiTE

CLRC July 2007

• TWiLiTE will demonstrate, for the first time, downward looking wind profiles from 18 km to the surface obtained with an airborne direct detection scanning Doppler lidar

• The TWiLiTE instrument is compact, rugged and designed for autonomous operation on the NASA WB57.

• TWiLiTE will be completed in summer 2008.

• The instrument could be transitioned to a UAV like Global Hawk .

Tropospheric Wind Lidar Technology Experiment (TWiLiTE) Instrument Incubator Program

UV Laser

Rotating HOE telescope

Doppler Receiver

TWiLiTE system integrated on WB57 3 foot pallet

CLRC July 2007

Airborne Doppler Lidar Wind Profiling

Lidar ranging permits determination of wind speed as a function of altitude.Multiple look angles permit determination of vector wind.

250 m

CLRC July 2007

TWiLiTE Target Platform

Modular palletNadir view

Payload mounting

110V, 4 X 25A, 3 phase, 400 Hz; 28V DC 35A

Payload Electrical Power

374 kg per pallet X 4 pallets.

Payload mass

200 m/s @ 18 kmCruise Speed

6.5 hoursDuration

18 kmMax. Altitude

WB57Specification

WB57 Aircraft: NASA Johnson Space Center

3’ instrument pallet

CLRC July 2007

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) (complete scan cycle) 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

CLRC July 2007

Wavelength 354.7 nmTelescope/Scanner Area 0.08 m2

Laser Linewidth (FWHH) 150 MHzLaser Energy/Pulse (6 W) 30 mJ @ 200 pps

(8 W) 40 mJ @ 200 ppsEtalon FSR 16.65 GHzEtalon FWHH 2.84 GHzEdge Channel Separation 6.64 GHzLocking Channel Separation 4.74 GHzInterference filter BW (FWHH) 120 pmPMT Quantum Efficiency 25%Optical Efficiency (Edge w/o BS or etalon) 0.37BS 0.41

TWiLiTE Instrument Parameters

CLRC July 2007

0 5 15 2010Altitude (km)

det

ecte

d p

hot

ons

104

105

106

107

black = overlap corrected, no max. count rateblue = overlap corrected, 50 MHz max. count rate

Photocounts Detected in each Edge Channel10 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.

CLRC July 2007

red = performance with current system parameters

blue = performance with expected system parametersA

ltit

ud

e (k

m)

L-O-S wind error (m/s)

Simulated L-O-S wind error

0

5

15

20

10

0.0 0.5 1.0 1.5 2.0

Current system performance (red curve) includes telescope with 58% diffraction efficiency and 55% encircled energy.

Expected system performance (blue curve) includes telescope with 62% diffraction efficiency and 82% encircled energy.

In both cases, the black curve is the performance with no solar background included.

TWILITE system performance

CLRC July 2007

8 point conical step stare scan pattern

Top view

Scanning parameters:

• Constant dwell of 10s/LOS

• Fixed azimuth increments of 45 deg in CW 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

CLRC July 2007

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

CLRC July 2007

Double Edge Etalon Channels

CLRC July 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

CLRC July 2007

TWiLiTE 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

CLRC July 2007

Assembled Receiver Components

CLRC July 2007

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

CLRC July 2007

Telescope Mechanical Design

Envelope Dimensions:25” Height30” Diameter (includes mounts and motor, 25” without)

Total Mass: 51 kg (112 lb)

3 mount points

CLRC July 2007

Laser Transmitter Specifications

Performance Specifications/Design Performance Summary Table

Parameter Specification Design Performance Margin

Wavelength 355 nm 355 nm NA

Laser Energy (UV) >30 mJ 40 mJ @ 1.3% duty cycle > 33%

Pulse Rep Rate 200 Hz 200 Hz NA

Average Power > 6 W 8 W @ 1.3% duty cycle > 33%

Beam Quality, M^2 < 3 < 2.5 17%

Energy in the Bucket > 86% encircled energy into 3x d. l. beam Meet specification TBD

Frequency Stability < 5MHz RMS for 30 sec

< 50 MHz RMS for 30 min

Meet specification

< 30 MHz RMS for 30 min

TBD

40%

Seeding Efficiency >99.9% >99.9 Meets spec

Pulsewidth > 15 ns ~13-15 ns None

Linewidth <120 MHz @ 355 nm ~120 MHz None

Pointing stability < 10% of beam divergence < 10% of beam divergence TBD

Electrical Power (excl. chiller) 550 W 470 W 14%

Thermal Management Conductive or Liquid Cooled Conductive to Liquid NA

Lifetime 1 billion shots (75% diode derating) @ 1064 nm 1 billion shots @ 1064 nm TBD

CLRC July 2007

Injection seeded Nd:YAG ring oscillator with single amplifier Frequency tripled to 355 nm Pulse energy = 30 mJ @ 355 nm Pulse Rep Frequency = 200 pps Optical canister is 28cm x 33 cm

Amplifier Compartment

Oscillator Compartment

Modulator & q-switch drive electronics

Ring oscillator

Amplifier

Resonance detection photodiode

Seed laser

THG

SHG

Laser Module Overview

Oscillator head

Isolator

Periscope

Front View

Coolant connector

Purge port

355 nm output window

1064 & 532 nm output window

See Hovis et al, “Advanced Transmitters for Ladar Applications” in Session 11

CLRC July 2007

TWiLiTE Assembly

1- Floor; 2- Mounting frame; 3- Optical bench (laser &HOE rotating telescope); 4- Receiver & Electronics ; 5- WB57 Pallet

1

2

3

4

5

Mass: 250 kgPower: 770W (not including heaters)

CLRC July 2007

Project Timeline

START:

AUG 2, 2005

SYSTEM REQ

WORKSHOP

DEC 1, 2005

CONCEPT

DES REVIEW

FEB 16, 2006

20

06

20

07

20

08

CRITICAL

DES REVIEW

MAY, 2007

TEST FLIGHTS

LATE SUMMER

2008

FINISH:

AUG 1, 2008

TELESCOPE

SUBSYS PDR

MAY 22, 2006

PRELIM DES

REVIEW

JUL 20, 2006

ETALON

DELIVERY

APR 2007

RECEIVER

DELIVERY

AUG 2007

LASER

DELIVERY

JUL 2007

RECEIVER

SUBSYS PDR

(GSFC IR&D)

MAR 2005

TELESCOPE

DELIVERY

AUG 2007

ASSEMBLY

INTEG & TEST

3Q/2007- 2Q/2008

CLRC July 2007

TWiLiTE Summary

• TWiLiTE 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.

• 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 will 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: ESTO IIP Program; Goddard Space Flight Center IRAD program

CLRC July 2007

Backups

CLRC July 2007

Mission Applications

Global Tropospheric Wind Sounder• Improved NWP• Hurricane and severe storm prediction

Airborne Doppler Lidar• Mesoscale research• Improved hurricane prediction• Satellite cal/val• Technology validation

Exploration •Martian winds from orbit or surface

CLRC July 2007

Doppler Lidar Measurement Concept

MOLECULAR DOPPLER RECEIVER • Molecular return gives lower accuracy and resolution but signal is always there

Double-edge filters sample wings of molecular spectrum to measure Doppler shift

CLRC July 2007

Double Edge Doppler Lidar Heritage

• In 1999 the first molecular “double edge” Doppler receiver was built as a proof of principle experiment.

• The molecular receiver was installed in the GLOW mobile Doppler lidar to demonstrate the functionality and scalability of the approach

• 5 years of ground based lidar wind measurements in a wide variety of conditions.

-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

m/s

deg

Double-edge filters sample wings of molecular spectrum to measure Doppler shift

GLOW mobile Doppler lidar

Receiver mounted in GLOW lidar for field tests and measurements

Time series of wind speed and direction profiles from IHOP_2002

CLRC July 2007

TWiLiTE IIP Overview

IPO

ESTO

SBIR

HARLIE

GLOW

CPL

TWiLiTE

• NASA IIP 2004

Started: Aug 1, 2005

3 year effort

• Leverages significant technology

investments and instrument

development heritage:

IR&D + SBIR + IPO + ESTO

•Laser – Fibertek

•Data System – Sigma

•HOE – Ralcon

•FP etalon – MAC

• Heritage from Fielded Lidar Systems:

GLOW, CPL, HARLIE

IR&D

Objective: Advance TRL of key enabling technologies for direct detection Doppler lidar including validation at the instrument system level from a high altitude aircraft

CLRC July 2007

System Block Diagram

Scanner Ctrl

Laser Power

Timing/Control

Data Acq.

Laser

Com

puter

HOE Scanner/Telescope

Laser Cooling

SIGNAL FIBER

ANALOG/PHOTON COUNTS, SYS DATA

Etalon Control

SYNCAUTOFOV TO COMP

Det. Box Temp

PRESSURE VESSEL

ETALON

Bm Exp

RE

CE

IVE

R T

EM

P C

ON

TR

OL

ETALON SPACING/PARALLELISM

A/D SIGNALFIBERWATERPOWER

AUTO TIP/TILT ADJ

INS/GPS Data

Power Dist/Sw

INS

/GP

S

MOLECULAR DE DOPPLER RECEIVER

PRESSURE VESSEL

PRESSURE VESSEL

PRESSURE VESSEL Window

CLRC July 2007

Rotating HOE Telescope

• Optical: laser, receiver, window

• Mechanical: optical bench, window, auto-alignment system (AAS)

• Thermal: environment-window-HOE, thermal system,

optical bench, payload bay environment

• Electrical: Data system, power

• Software: Command & control, scan position, boresight,

data

Laser

SIGNAL FIBER

AFT OPTICS

INS

/GP

S

Window

HOE

Mot

or

Cmd & Data

Data

Data

Fine Steering Mirror

Auto-alignment

CLRC July 2007

TWiLiTE Predicted shot noise limited LOS error2000 shot average, 250 m vertical resolution, background aerosol