An Alternative Direct Detection Approach to Doppler Winds that is

Independent of Aerosol Mixing Ratio and Transmitter Frequency Jitter

Ball Aerospace & Technologies Corp.

Presented by: Chris Grund cgrund@ball.com, 303-939-7217

Presented to: Space Winds Lidar Working GroupMiami, Florida

2/8/2007

OAWL Theory

3

Optical Autocovariance TheoryOptical Autocovariance Theory

V = * * c / (4 * (d2-d1))

Optical Autocovariance Wind Lidar:

OAWLPronounced: ALL

50 40 30 20 10 0 10 20 30 40 500

0.5

1

1.5

2

2.5

Wavelength Shift (m/s)

Backscatter (W)

Pulse Laser

d2

d1

Det

ecto

r 1

Det

ecto

r 2

Det

ecto

r 3 Data

System

CH 1

CH 3

CH 2

From Atmosphere

Stepped mirror

BeamSplitter

0 200 400 600 800 10000

0.2

0.4

0.6

0.8

1

Distance d2-d1

Arb

itra

ry I

nten

sity

CH 1

CH 3

CH 2

CH 2CH 1

CH 3

Doppler shiftedAtmosphericReturn at t>0

Laser at t=0

M W

ings

A+MAerosol +center of molecular

ReceiverTelescope

Doppler ShiftDue to wind

AM

A+M+BG

BG

Return spectrum from aMonochromatic source

Measured as a fraction

Pre

filte

r

Note: Scale of molecuar and cycle of autocovariance function are arbitraqry for illustration

4

OAWLOAWL Advantages Advantages

Laser simplifications:

• Injection seeding not necessary

• Shot to shot mode hopping no problem

• Passive Q-switch feasible – no HV

• No 800 km coherence length LO needed

• No hardware correction for spacecraft V

Receiver:

• One system for whole atmosphere

• Aerosol and molecular in one

• No calibration dependence on targets

• Mixed aerosols, clouds, molecules OK

• No clean/dirty air calibration bias

• No absolute frequency lock to laser

• No absolute temperature controllers

• No spectral drift calibration requirement

OAWL OAWL does it ALLdoes it ALL

5

OAWL Combines/Augments the Best Traits of Both OAWL Combines/Augments the Best Traits of Both Coherent and Incoherent Lidar MethodsCoherent and Incoherent Lidar Methods

Yes

Yes

Yes (UV laser)

Yes

Maybe/Yes

Maybe

Yes (UV laser)

Yes

No

Some

No (IR laser)

N/A

Synergies/Compatibilities

HSRL (calibrated aerosols/clouds)

DIAL (chemical species)

Raman (Chemical species, T, P)

Photon counting potential (next time!)

Yes

Yes

No

Yes

Yes

Yes

Yes

No

Yes

No

No

No

Phenomenology

Measure Aerosol

Measure Molecular

Sensitive to Aer/Mol mixing ratio

Full precision 0-20 km profile

None

3(6)

Yes

No

None

Many

Yes

Maybe

>800 km

1

No

Yes

Receiver

Reference laser coherence length

Detector Elements

Single multi-speckle averaging/shot

Orbital velocity correction in hardware

Single/hopping OK

No

Single/stable

Yes

Single/stable

Yes

Transmitter

Laser Mode

Absolute frequency lock

Direct Detection OAWL

Direct DetectionEtalons (edge/image)

Coherent Detection

Challenges

Brassboard Development

7

Demonstration System ArchitectureDemonstration System Architecture

Stepped Mirror

Field Stop

Interferometer

Detector/ Amp 2

Detector/ Amp 3

Detector/ Amp 1

Windows PC-based Data System

(Labview) 6” dia., f/8 Newtonian Telescope

Display

3-D Sonic Anemometer

Separator Mirror

Beam Sample

Interferometer quality

Pulse Laser 100 μJ /pulse, 1 kHz rate

Beam Expander

IM1

2IM

Transmitter

8

The Brassboard SystemThe Brassboard System

3-BeamInterferometer

Assembly

3 DetectorAssembly

Laser TransmitterAssembly

Laser Controller

Alignment Camera and Monitor

PC Data System

COTS NewtonianReceiver Telescope

0-Range, 0-VelocitySampling Assembly

Receiver Field Stop

Channel Splitting Mirror

9

Development Team Development Team

Mick Cermak – Lab and fabrication support, experiment support and logistics

Dina Demara – Data system software

Doug Frazier – brassboard mechanical design

Dennis Gallagher – final brassboard optical design and modeling (left Ball in ’06)

Chris Grund – PI, system and experiment design, signal processing, calibration, validation

Bob Pierce – ongoing optical engineering, experiment support

Ron Schwiesow – proposed original concept (retired from Ball 10/05)

Michelle Stephens – Spaceborne performance modeling

Steve Stone – Procurement assistance, electronics support

Internal R&D funding support through Ray Demara gratefully acknowledged

Proof of Concept Testing

11

Proof of Concept Test RangeProof of Concept Test Range

OAWL System in Lab

Turning Mirror

Sonic Anemometer

Focal volume

Lidar beam pathTerminal Beam Block

FA Cleanroom Building Rooftop at Ball Aerospace in Boulder, CO

12

First light – Experimental Intensity SNRFirst light – Experimental Intensity SNR

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

-50 0 50 100 150 200 250

Range (m)

Volts from detector

0-range sample(wire works asdesigned for cal)

Molecular+aerosol scattering

Terminal range - black targetat 90 m

Focus range60 m

60m SNR on atmosphere:13 dB optical (26 dB elec.)(expect 11 dB = validates model within

backscatter and detector uncertainty)

Conditions:1 kHz rep rate16 shot average (7 dB single shot)full sun daytime/filter inthrough interferometer3-beams to 1 detectorblack illustration board targetBW: 150 MHz* No field stop

RMS Noise0.0073V

Signal0.15V

0-range0-velocitysample

13

First OAWL POC Wind RetrievalsFirst OAWL POC Wind Retrievals(December 2006) (December 2006)

Red: Anemometer-OA cross correlation White: anemometer autocorrelationBlue: cross correlation for pure Gaussian noise distributions

~1 m/s random error with ~0.6 m/s bias demonstrated with 0.3 s averaging and 3m range resolution. Excellent fluctuation correlations.

14

First Wind Retrievals- continuedFirst Wind Retrievals- continued

Statistically very different wind set (see anemometer autocorrelation function)• again excellent fluctuation correlations• OAWL brassboard: ~1.2 m/s random error, with 0.15 m/s bias (3m res, 0.3 s avg)

Preliminary

OAWL Space Lidar Winds

Performance Modeling

16

Performance Requirements Addressed (so far)Performance Requirements Addressed (so far)for OAWL Space Wind Lidar Operationfor OAWL Space Wind Lidar Operation

From: Kavaya and Gentry: Status of Laser/Lidar Working Group Requirements

Demo Threshold Objective

Vertical depth of regard (DOR) 0-20 0-20 0-30 km

Vertical resolution: Tropopause to top of DOR Top of BL to tropopause (~12 km) Surface to top of BL (~2 km)

Not Req.21

Not Req.1

0.5

20.5

0.25

kmkmkm

Horizontal resolution 350 350 100 km

Velocity error Above BL In BL

32

32

21

m/sm/s

Minimum wind measurement success rate 50 50 50 %

17

Preliminary OAWL System PerformancePreliminary OAWL System Performancefor Spaceborne Operationsfor Spaceborne Operations

Conditions:Wavelength 355 nmPulse Energy 550 mJ Pulse rate 50 HzReceiver diameter 1mLOS angle with vertical 450

Vector crossing angle 900

Horizontal resolution 350 kmOPD 1 mSystem transmission 0.35Alignment error 5 μRBackground bandwidth 35 pmOrbit altitude 400 kmVertical resolution 1 kmPhenomenology CALIPSO model

0 0.5 1 1.5 2 2.5 30

5

10

15

20

altitude (km)

Velocity error (m/sec)

Daytim

e

Nig

httim

e

Horizontal Wind Velocity Error (m/s)

A

ltit

ud

e (

km)

Objective

Demo&

Threshold

Wrap-up

19

ConclusionsConclusions

Optical Autocovariance Wind Lidar (OAWL) has advantages for space operations

Potentially, one system DOES IT ALL, from and boundary layer to free trop

Simpler laser

• Injection seeding not needed, passive Q-sw feasible

• single mode per pulse, but pulse to pulse frequency hopping OK

No velocity calibration dependence on aerosol/molecular backscatter mixing ratio

Laser coherence length only needs to exceed the interferometer path length

Compatibility with secondary aerosol or chemical species missions

First OAWL brassboard lidar completed, aligned, and calibrated in 2006

Developments ongoing, intercomparison campaign sought (NOAA, NASA)

Successful, range-resolved atmospheric proof of concept tests completed

Preliminary wind retrieval/calibration algorithms developed/working

Measurements validate brassboard system performance model and hardware

20

What’s in the works?What’s in the works?

Improved 0-velocity, 0-range sampling apparatus in progress for brassboard

Ruggedizing and field enclosure for brassboard cross-validation

Field test alongside existing wind lidar system. Perhaps the NOAA/ETL HRDL system.

Design (in progress this year) and construction (next year?$$$) of a ruggedized, field-widened receiver suitable for aircraft testing, environmental testing to achieve TRL 6

Evaluating laser scaling issues and options.

Extensive performance model development based on the validated CALIPSO model, but including detailed OAWL components, wind mission scenarios, and spacecraft interactions.