OAWL System Development Status C.J. Grund, J. Howell, M. Ostaszewski, and R. Pierce Ball Aerospace &...

OAWL System Development Status

C.J. Grund, J. Howell, M. Ostaszewski, and R. PierceBall Aerospace & Technologies Corp. (BATC), [email protected]

1600 Commerce St. Boulder, CO 80303

Working Group on Space-based Lidar WindsWintergreen, VA

June 17, 2009

Agility to Innovate, Strength to Deliver

Ball Aerospace & Technologies Corp.

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Acknowledgements

The Ball OAWL Development Team:

Jim Howell – Systems Engineer, Aircraft lidar specialist, field work specialist

Miro Ostaszewski – Mechanical Engineering

Dina Demara – Software Engineering

Michelle Stephens – Signal Processing, algorithms

Mike Lieber – Integrated system modeling

Kelly Kanizay – Electronics Engineering

Chris Grund – PI system architecture, science/systems/algorithm guidance

Carl Weimer – Space Lidar Consultant

OAWL Lidar system development and flight demo supported by

NASA ESTO IIP grant: IIP-07-0054

OAWL: Optical Autocovariance Wind Lidar

Ball Aerospace & Technologies

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Aerosol WindsLower atmosphere profile

Addressing the Decadal Survey 3D-Winds Mission withAn Efficient Single-laser All Direct Detection Solution

Integrated Direct Detection (IDD) wind lidar approach: Etalon (double-edge) uses the molecular component, but largely reflects the aerosol. OAWL measures the aerosol Doppler shift with high precision; etalon removes molecular backscatter

reducing shot noise OAWL HSRL retrieval determines residual aerosol/molecular mixing ratio in etalon receiver, improving

molecular precision Result:

─ single-laser transmitter, single wavelength system─ single simple, low power and mass signal processor─ full atmospheric profile using aerosol and molecular backscatter signals

Ball Aerospace patents pending

Telescope

UV Laser

Combined Signal

Processing

HSRL Aer/mol mixing ratio

OAWL Aerosol Receiver

Etalon Molecular Receiver

Molecular WindsUpper atmosphere profile

1011101100Full

Atmospheric Profile Data


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Purpose for OAWL Development and Demonstration

OAWL is a potential enabler for reducing mission cost and schedule─ Similar to 2-m coherent Doppler aerosol wind precision, but requires no additional laser─ Accuracy not sensitive to aerosol/molecular backscatter mixing ratio ─ Tolerance to wavefront error allows heritage telescope reuse and reasonable optics

quality─ Compatible with single wavelength holographic scanner allowing adaptive targeting if

there is need─ Wide potential field of view allows relaxed tolerance alignments similar to CALIPSO ─ Minimal laser frequency stability requirements─ LOS spacecraft velocity correction without needing active laser tuning

Opens up multiple mission possibilities including multi- HSRL, DIAL compatibility

Challenges met by Ball approach─ Elimination of control loops while achieving 109 spectral resolution─ Thermally and mechanically stable, meter-class OPD, compact interferometer─ High optical efficiency─ Simultaneous high spectral resolution and large area*solid angle acceptance providing practical

system operational tolerances with large collection optics


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Optical Autocovariance Wind Lidar (OAWL) Development Program

Internal investment to develop the OAWL theory and implementable flight-path

architecture and processes, performance model, perform proof of concept

experiments, and design and construct a flight path receiver prototype.

NASA IIP: take OAWL receiver as input at TRL-3, build into a robust lidar

system, fly validations on the WB-57, exit at TRL-5.


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Ball Flight-path, Multi-wavelength, Field-widened OA Receiver IRAD Status


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OAWL Receiver IRAD Objectives

Develop and implement a practical flight-path OAWL receiver with minimal calibration requirements and free of active spectral control systems, suitable for aircraft operation

Develop/implement an OA receiver suitable for simultaneous multi-winds and HSRL

Develop/demonstrate permanent, flight-compatible, stable high precision interferometric optical alignment and mounting methods and processes

Develop appropriate radiometric and system integrated models suitable for predicting OAWL airborne and space-based performance


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OAWL IRAD Receiver Design Uses Polarization Multiplexing to Create 4 Perfectly Tracking Interferometers

• Mach-Zehnder-like interferometer allows 100% light detection on 4 detectors

• Cat’s-eyes field-widen and preserve interference parity allowing wide alignment tolerance, practical simple telescope optics

• Receiver is achromatic, facilitating simultaneous multi- operations (multi-mission capable: Winds + HSRL(aerosols) + DIAL(chemistry))

• Very forgiving of telescope wavefront distortion saving cost, mass, enabling HOE optics for scanning and aerosol measurement

• 2 input ports facilitating 0-calibration

Ball Aerospace & Technologies patents pending

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What’s So Special About the Cat’s-eye Interferometer?


Allows use of heritage telescope designs (e.g. Calipso) for space system - cost, mass, risk─ highly tolerance to wavefront errors─ Very large field of view (>>4mR) capable while maintaining high spectral resolution (~10 9, similar to

coherent detection systems)

Allows use of Holographic Optical Element beam directors and scanners even for high resolution aerosol 355nm wind measurements - cost, mass, pointing agility (other missions?)

Relaxes receiver/transmitter alignment tolerances - cost, performance risk─ Practical on-orbit thermal tolerances─ Enables single material athermal interferometer design

Enables wind and multi- aerosol missions with common transmitter and receiver - cost, sched.─ Simultaneous multi-wavelength capable interferometer suitable for HSRL and winds

Enables very high resolution passive and active imaging interferometry – potential for new earth and planetary science instruments with enhanced performance

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OAWL Receiver

A few simple components• Detector housings• Monolithic interferometer• Covers and base plate

mount to a monolithic base structure.

Detector amplifiers and thermal controlsare housed inside the receiver.


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OAWL Receiver In Assembly 109 Class Spectral Resolution Without Active Stabilization

Flowtron stand will also be used to hold the complete

lidar system rotated to point up for ground testing


Interferometric stability tests in progress

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Cat’s Eye Interferometer : Successful Primary Mirror Bond Tests

Current (Final) Bond Test(PhaseCam image)

Reference

Test Mirror

1/4 Wave PV @ 633 nm difference

Start: 24°C

Middle: 41°C

End: 23°C

Thermal Tilt Test Recovery

Reference

Test Mirror


Reference mirror Test mirror

Achieving 109 spectral resolution without active control systems is feasible!

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Receiver Development: Schedule Impacts and Status

Vendor could not deliver aluminum interferometer mirrors with promised wavefront precision.

─ Solution: new fused silica mirrors produced; bonded to aluminum holders. ─ Status: Resolved. Optics: good; Interferometric optic bond to aluminum: good─ Impacts: 3 month delay for optics; athermalization less but OK since IIP system operates at the

same fixed temperature used during alignment (30-35 C)

Vendor could not deliver cube beamsplitters to promised specs WRT splitting ratio and wavefront quality at 355nm.

─ Solution: cube beamsplitters replaced by plates; structure/holders modified to accommodate─ Status: Resolved. Optics: good; structure/holders modified─ Impacts: 5 month delay for optics and mods

Excess shrinkage during cure, and insufficient thermal stability of interferometric potting─ Solution: experiment with lower cure shrinkage materials, improved application process─ Status: Resolved, test results: good. Final optic will have 10 nm level compensation for any

residuals from all other components.─ Impacts: 3.5 months of spiral development


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OAWL IRAD Receiver Development Status

Receiver Status (Ball internal funding): Optical design PDR complete Sep. 2007 Receiver CDR complete Dec. 2007 Receiver performance modeled complete Jan. 2008 Design complete Mar. 2008 COTS Optics procurement complete Apr. 2008 Major component fabrication complete Jun. 2008

(IIP begins------------------------------------------------------------------------ Jul. 2008) Custom optics procurement vendor issues Aug. 2008

─ Custom optics procurement complete Dec. 2008

─ Accommodating rework complete Jan. 2009 Interferometric optics/mount bonding complete Feb. 2009 Interferometric alignment bond tests shrinkage / thermal issues Feb. 2009

─ New materials/process/mount design complete May, 2009 Assembly and Alignment in progress Late Jun. 2009 Preliminary testing scheduled Jul.

2009 Delivery to IIP scheduled Late Jul 2009


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OAWL System NASA-funded IIP


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OAWL IIP Objectives

Demonstrate OAWL wind profiling performance of a system designed to be directly

scalable to a space-based direct detection DWL (i.e. to a system with a meter-class

telescope 0.5J, 50 Hz laser, 0.5 m/s precision, with 250m resolution).

Raise TRL of OAWL technology to 5 through high altitude aircraft flight

demonstrations.

Validate radiometric performance model as risk reduction for a flight design.

Demonstrate the robustness of the OAWL receiver fabrication and alignment methods against aircraft flight thermal and vibration environments.

Validate the integrated system model as risk reduction for a flight design.

Provide a technology roadmap to TRL7


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OAWL IIP Development Process

Provide IRAD-developed receiver to IIP: Functional demonstrator for OAWL flight path receiver design principles and assembly processes. (entry TRL 3)

Shake & Bake Receiver: Validate systemdesign and test for airborne environment

Integrate the OAWL receiver into a lidar system: add laser, telescope, frame, data system, isolation, and autonomous control software in an environmental box

Validate Concept, Design, and Wind Precision Performance Models from the NASA WB-57 aircraft (exit TRL 5)


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OAWL Validation Field Experiments Plan

1. Ground-based-looking upSide-by-side with the NOAA High Resolution

Doppler Lidar (HRDL)

2. Airborne OAWL vs. Ground-based Wind Profilers and HRDL

(15 km altitude looking down along 45° slant path (to inside of turns).

Many meteorological and cloud conditions

over land and water)


Jan 2010

Fall 2010

NOAA HRDL 2m Coherent Doppler Lidar

OAWL System

Leg 1Leg 2Multipass

** Wind profilers in NOAA operational network

Platteville, CO

Boulder, CO Houston, TX

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OAWL IIP System Arrangement in WB-57 Pallet


Laser Power Supply

Pallet Frame

Custom Double Window

Laser

Wire Rope Vibration Isolators

Lifting Hooks

Telescope Primary Mirror

Sub-Bench with Depolarization Detector

Receiver

Telescope Secondary Mirror

ChillerOptic Bench

Thermal Control Isolation

Data Acquisition Unit

Power Condition Unit

ElectronicsRack

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OAWL Optical System

Interferometer Detectors (10)

Telescope

Laser

Zero-Time/OACF Phase Pulse Pre-Filter


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IIP Optical System Exploded View


Top Pallet Cover

Pallet Base with Window

OAWL Optical System

Thermal Control Insulation Panels

Thermal Control Insulation Panels

Electronics Rack

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Data System Overview

Data system architecture─ Based on National Instruments PXI Chassis─ Utilizes mostly COTS Hardware─ Custom (Ball) ADC daughter card on NI FPGA interface card─ Custom (Ball) FPGA code to implement photon counting

channels on NI card─ Labview code development environment

Challenges & Solutions─ Reduced air pressure at altitude degrades heat removal ability

of stock cooling fans Upgrade cooling fans, add fans as needed Test system in altitude chamber

─ Jacket material used in COTS cables is PVC, which is not permitted on WB-57

Utilizing NI terminal strip accessories where possible Fabricating custom cables made from allowable jacket materials


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Taking an OAWL Lidar System Through TRL 5

NASA/ESTO Funded IIP Plan:

Program start, TRL 3 complete Jul. 2008 TRL-3

IRAD receiver delivered to IIP planned Jul. 2009

Receiver shake and bake (WB-57 level) planned Aug. 2009

System PDR/CDR complete Feb./Mar. 2009

Lidar system design/fab/integration complete May 2009

Ground validations completed planned Mar. 2010 TRL-4

Airborne validations complete (TRL-5) planned Dec. 2010 TRL-5

Receiver shake and bake 2 (launch level) planned Apr. 2011

tech road mapping (through TRL7) planned May 2011

IIP Complete planned June 2011


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Conclusions

All vendor component performance and flight-path process related issues have been overcome for the multi- (355nm, 532nm), field-widened, flight-path receiver.

The receiver is expected to be available to the IIP this August. Late delivery causes slightly delays in ground tests but airborne tests still on schedule.

IIP system development progress: Optical and mechanical design complete; CDR complete, major procurements underway and fabrication has started. Aircraft plans in place and flight conops understood. Ground validation plans in progress

Ground testing moved from December 2009 to in late January 2010.

WB-57 flight tests remain on track for Fall 2010 (TRL 5)


BackupsBackups

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On/Off line DIAL wavelength jump typically 10’s GHz

Optical Autocovariance lidar (OAL) approach - Theory

No moving parts / Not fringe imaging Allows Frequency hopping w/o re-tuning Simultaneous multi-operation

Optical Autocovariance Wind Lidar (OAWL):Velocity from OACF Phase: V = * * c / (4 * (OPD)) OA- High Spectral Resolution Lidar (OA-HSRL): A = Sa * CaA + Sm * CmA , = Sa * Ca + Sm * Cm

Yields: Volume extinction cross section, Backscatter phase function, Volume Backscatter Cross section, from OACF Amplitude

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

Phase Delay mirror

BeamSplitter

ReceiverTelescope

Pre

filte

rOPD=d2-d1

Simplest OAL(Not the IIP config)

Frequency

Ball Aerospace & Technologies = phase shift as fraction of OACF cycle

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OAWL Optical System Details

Pre-Filter

Depolarization Detector Module


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Ball Space-based OA Radiometric Performance Model –Model Parameters Using : Realistic Components and Atmosphere

LEO Parameters WB-57 Parameters

Wavelength 355 nm, 532 nm 355 nm, 532 nm

Pulse Energy 550 mJ 30 mJ, 20 mJ

Pulse rate 50 Hz 200 Hz

Receiver diameter 1m (single beam) 310 mm

LOS angle with vertical 450 45°

Vector crossing angle 900 single LOS

Horizontal resolution* 70 km (500 shots) ~10 km (33 s, 6600 shots)

System transmission 0.35 0.35

Alignment error 5 R average 15 R

Background bandwidth 35 pm 50 pm

System altitude 400 km top of plot profile

Vertical resolution 0-2 km, 250m 100m (15m recorded)

2-12 km, 500m

12-20 km, 1 km

Phenomenology CALIPSO model CALIPSO model

-scaled validated CALIPSO Backscatter model used. (-4 molecular, -1.2 aerosol)

Model calculations validated against short range POC measurements.


10-8

10-7

10-6

10-5

10-4

0

5

10

15

20

backscatter coefficient at 355 nm m-1 sr-1A

ltitu

de, k

m

aerosol

molecular

Volume backscatter cross section at 355 nm (m-1sr-1)A

ltit

ud

e (

km)

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OAWL – Space-based Performance: Daytime, OPD 1m, aerosol backscatter component, cloud free LOS


0

2

4

6

8

10

12

14

16

18

20

0.1 1 10 100Projected Horizontal Velocity Precision (m/s)

Alt

itu

de

(km

)

355 nm

532 nm

Demo and Threshold

Objective

Threshold/Demo Mission Requirements

250 m

500 m

1km

Ver

tica

l A

vera

gin

g (

Res

olu

tio

n)

Objective Mission Requirements

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Looking Down from the WB-57 (Daytime, 45°, 33s avg, 6600 shots)

0

2

4

6

8

10

12

14

16

18

0 0.1 0.2 0.3 0.4 0.5 0.6

Velocity Precision (m/s)

Alt

itu

de

(k

m)

355nm532nm


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