1. Working Group on Space-based Lidar Winds
Space-based Integrated Wind, Aerosol, and Chemistry Lidar Christian J. Grund Ball Aerospace & Technologies Corp. (BATC), 1600 Commerce St. Boulder, CO August 4, 2011
Working Group on Space-based Lidar Winds
Boulder, CO

2. Motivation
The needs for space-based wind lidar have been well documented by Baker, Hardesty, Atlas and others in this working group, but there are other critical environmental measurement needs that might be served or augmented by combining wind and other mission instruments.
Cost impetus
Decadal survey missions are 3/4 - >>1 Billion dollar class
Schedule have stretched and may stretch further due to costs, complexity, and shrinking resources
Increasingly austere times suggest that combining missions may be necessary to accomplish the desperately needed science and observational data in a timely fashion
Can winds mission costs be shared with other missions? Can some other mission goals be satisfied by SEVERAL winds missions with other capabilities?
Science data impetus – common themes
Aerosol needs
Climate
Safety and health - volcanic plumes, visibility, air quality
Chemistry needs
Air quality, climate CO2, O3, H2Ov, CO, NO2, SO2
Can science data be enhanced with coincident winds?

3. Planned Decadal Survey Missions Can Benefit from Cost, Mass, and Power Saving Technologies and Enhanced Science Data Optical Autocovariance Lidar (OAL) Potentials
Decadal survey missions that can potentially benefit from OAL are:
ACE – aerosol and cloud types and properties; Ocean surface layer organics
OAL: Calibrated aerosol optical property profiles at multiple l’s, combined with winds
ASCENDS – CO2 column content –sources and sinks
OAL: combined with winds to provide flux
GEO-CAPE – ID of human vs. natural sources of aerosols and O3 precursors
Ocean color and gas content radiometry correction for aerosols/clouds from a wind/HSRL lidar?
GACM – O3 profiles and precursors; global aerosol and air pollution transport
OAL: UV O3 lidar that also provides LOS winds and calibrated aerosol properties
3D-Winds – vertical profiles of the horizontal wind from aerosol and molecular backscatter
OAWL provides mass (maybe 50%), power, risk, and cost reductions by enabling coherent DWL quality wind profiles from aerosol returns at 355 nm enabling am efficient single laser all direct detection hybrid (aerosol/molecular) lidar. ADM/ALADIN is also all direct detection, but with much lower photon efficiency and much higher alignment tolerance needs.

4. Objective
As this group knows, Ball Aerospace has been developing Optical Autocovariance Lidar (OAL) over the past few years, with recent demonstration for winds (OAWL)
In addition to winds, OAL can also efficiently enable simultaneous multi-l High Spectral Resolution Lidar (OA-HSRL or HOAWL) aerosol profiling and facilitate Differential Absorption Lidar (OA-DIAL) chemistry capabilities with a single receiver/optical system
OAL has some uniquely enabling capabilities for multimode science data missions
This talk is not a comprehensive overview of all approaches, but discusses the measurement synergies inherent in the OAL detection approach, and as a challenge to find ways to rein in mission costs without sacrificing (and possibly enhancing) science data

5. Introduction: What is Optical Autocovariance Lidar (OAL)?
Method:
Interferometric direct detection lidar
Instantaneous measurement of the phase and amplitude of the optical autocovariance function (OACF) about one Optical Path Difference (OPD)
Key Attributes:
Very high spectral resolution feasible
Self-referenced optical mixing
intensity measurements carry optical freq. info.
minimizes required electronic bandwidth
minimizes required signal processing power
Eliminates need to tune receiver to transmitter
Hardware-free compensation for LOS orbital V
Applications:
Doppler Lidar (wind profiles)
High Spectral Resolution Lidar (HSRL)
Differential Absorption Lidar (DIAL)

6. Optical Autocovariance Wind Lidar (OAWL)

7. Optical Autocovariance Wind Lidar (OAWL)
The phase of the OACF for 0-velocity at 0-range is captured by locally sampling the outgoing pulse.
The OACF is measured for the atmospheric return from each range bin.
The wind velocity V is calculated from the difference in the OACF phase (Df) between the 0-velocity sample and each range return:
V = l *Df * c / (2 * OPD)
Df expressed as a fraction of 1 OACF period
Doppler Winds use the Phase of the OACF

8. OAWL Design Implemented in IIP Uses Polarization Phase Delays and Multiplexing to Implement 4-Phase-Delay Interferometers in the Same Optical Volume – Field Widened for Practical Alignment Tolerance and Etendu
Mach-Zehnder-like interferometer allows 100% light detection on 4 detectors
Cat’s-eyes field-widen to preserve interferometric contrast allowing wide alignment tolerance, practical simple telescope optics
Receiver is achromatic, facilitating simultaneous multi-l operations (multi-mission capable: Winds + HSRL(aerosols) + DIAL(chemistry))
Very forgiving of telescope wavefront distortion (a few l OK) saving cost, mass, enabling HOE optics for scanning and aerosol measurement
2 input ports facilitating 0-calibration time and wind speed
$$$
New material
Shows a top level system architecture diagram of the new OAWL receiver .
No components are identified.
Lists benefits over previous technology.
$$$
Patented and patents pending

9. Why Optical Autocovariance Lidar for winds?
Uses narrow bandwidth laser transmitter at any wavelength where good intensity detectors are available.
High Spectral Resolution means high velocity resolution (on aerosol returns)
Virtually unlimited transverse speckle acceptance allows wide scaling for power-aperture product, liberal alignment tolerances, and good single shot intensity estimation (important for aerosol and chemistry)
Spectral and radiometric efficiency- even to the extent of enabling Doppler winds from Geostationary Orbit for full time regional coverage
OAL will work at any wavelength where good detectors exist, analog or photon counting
Simultaneous multi-wavelength High Spectral Resolution Lidar capability
to understand aerosol optical and physical properties; categorizing source regions
Facilitates relatively low cost construction (Al construction, potted optics)
109 resolution without active receiver or receiver/transmitter controls saving cost and complexity
OAWL does not require hardware laser frequency adjustment for LOS velocity

10. OAWL – Space-based Performance: Daytime, OPD 1m, aerosol backscatter component, cloud free LOS
Threshold/Demo Mission Requirements
250 m
500 m
1km
Vertical Averaging (Resolution)
Objective Mission Requirements
New material
Latest hypothetical space prerformance predictions against customer given requirements, showing available margin
Similar to previously approved

11. OA-HSRL (aka HOAWL when combined with winds)

12. High Spectral Resolution Lidar Optical Autocovariance (OA-HSRL) for Calibrated Aerosol Measurements
HSRL Retrieval of Sa and Sm from OA-HSRL fit:
Sa+m = Received signal – BL = Sa + Sm
A = Sa * CaA + Sm * CmA
Q = Sa * CaQ + Sm * CmQ
Sm = (CaA* Q - CaQ * A) / (CaA * CmQ – CmA * CaQ)
Sa = (CmQ* A - CmA* Q) / (CaA * CmQ – CmA * CaQ)
(For OA-HSRL CaA1, CaQ0, CmA0, CmQ1)
Aerosol Extinction:
(bm is the molecular volume extinction cross section that is calculated from air density profile)
Aerosol Scattering Cross Section:
ba(R) = w0(R) * (be(R) – bm(R))
(assumes w0 ~1, single scatter albedo)
Aerosol Backscatter Phase Function:
Fa/4p = (3/8p) * Sa(R) * bm(R) / (Sm(R) * be(R) )
(for air molecules the backscatter phase function is: Fm/4p = 3/8p)
OA-HSRL uses the Amplitude of the OACF, phase does not matter

13. Why Optical Autocovariance Lidar for aerosols?
Photon efficiency  better swath sampling with more simultaneous beams for a given laser power consistent with ACE goals
Consider 2-1m telescopes with 4 fwd and 4 aft views, or a single 1m-telescope and a rotating holographic scanner (should work fine for OAWL due to wavefront tolerance)
Winds+HSRL (wind optimization drives OPD longer) lower combined mission cost if the sampling issues can be addressed
Possibilities:
instead of 2 separate missions (e.g. 3D-Winds and ACE), how about 2 identical Wind+HSRL missions lower cost instrument, redundancy factor, higher sampling density for winds and aerosols. 1m, forward with 4 or more across-track beams, 1m aft with 4 or more across track beams. Could be near simultaneous vector overlap in the boundary layer,
Multiple wavelengths for aerosols also provide improved sampling for winds – lower extinction, ~2X the measurement rate
Winds+HSRL  Direct measurement of LOS aerosol flux greater science content
Simultaneous multi-wavelength HSRL (and depolarization ratio) without active tuning least complexity/cost/mass for enhanced aerosol science content
OA-HSRL can use a single frequency-but unlocked laser  passive Q-switch  mass, HV, complexity, cost savings, improved mission reliability, pulse energy stability
T0 phase is NOT required for HSRL (if no winds), any relative frequency will do!!

14. OA-HSRL: Daytime Space-based Performance
Wavelength nm, 532nm
Pulse Energy mJ
Pulse rate Hz
Receiver diameter 1m (single beam)
LOS angle with vertical 45 deg
System transmission
Background bandwidth pm
Orbit altitude km
Vertical resolution 750m
Phenomenology CALIPSO model

15. OA-Differential Absorption Lidar (OA-DIAL) for chemistry and species flux

16. Optical Autocovariance Differential Absorption Lidar (OA-DIAL)
1 Intensity
Data Stream-
4 channels
OA-DIAL
OA-HSRL
(Vis-UV only)
OAWL
Data Products
NIR – UV OK
Control and
Data
Acquisition
On-Off line laser
Expander
Scanner
or FOV
Switcher
OAWL Receiver
Telescope
OA-DIAL uses the Total Return Signal Power
Independence of the receiver from specific wavelength saves mass, power, complexity, and mission cost.
LOS aerosol corrections and aerosol flux measured simultaneously with OA-HSRL.
Achromatic OA-x hardware design facilitates wide multiwavelength operation.
High potential for combined missions at significant cost/mass savings with enhanced science potential
Ball Aerospace & Technologies

17. Note synergies between HSRL and DIAL measurements
Why Optical Autocovariance Lidar for chemistry? Differential Absorption Lidar (DIAL)
Many species are measurable, of particular interest to Decadal Survey Missions are O3, H2Ov, CO2 , SO2, NO2
Atmospheric studies generally require fluxes of atmospheric constituents.
Flux = N(x,y,z)*V(x,y,z) both species concentration (N) and wind velocity (V) are needed
In current mission scenarios, species concentration and winds are generally measured by two separate instruments, or use winds derived from forecasts or models with separate species measurements.
Poor coincidence in space, time, and resolution between winds and concentrations is a common and significant error source, often limiting the utility of the measurements.
Differential Absorption Lidar (DIAL) is a lidar technique used to measure range resolved species concentration (N(R)) by observing signal returns on and off an absorption line:
Note synergies between HSRL and DIAL measurements
Ball Aerospace & Technologies

18. Integrated Direct Detection (IDD) Hybrid Doppler Wind Lidar
Putting it Together: Notional Efficient Multimode OAL Lidar Architecture
Integrated Direct Detection (IDD)
Hybrid Doppler Wind Lidar
Aerosols, Chemistry,
and Winds
Scanner or
Switcher
(One set of 4 per l)
UV 355nm or Freq.
Agile Laser

19. Beyond or as an Adjunct to the Decadal Survey Missions: What About GEO
Shown feasible: A staring photon counting DWL with a 3 o x 3o field of regard capable of monitoring, e.g., tropical cyclogenesis or severe storm formation regions. Both communications satellite hosted payload (fitting small sat Venture class missions) and full scale dedicated observatory missions are feasible. Single LOS configuration shown (relies on continuity in time or spatial clusters for vector equivalency. Other configurations can measure vector winds directly). Extension to aerosols and chemistry is likely feasible.
Evolving concept presentations at past on space-based lidar winds working group meetings:
Snowmass, CO 7/07, radiometric feasibility; Destin, FL 2/10, practical model with geometry; Wintergreen, VA 8/11, improved model predictions and practical hardware concept; Boulder, CO 8/2011 conflict resolved with prior analyses

20. Conclusions
The Optical Autocovariance Lidar approach has several inherent characteristics that reduce laser and optical system requirements for winds and combined wind-aerosol-chemistry systems potentially saving mask, risk, and cost
Combining missions could be considered for overall science data collection cost saving
Multiple copies of combined instruments, may save some cost over separate missions, and may enhance sampling coverage and redundancy
Adding winds to aerosol and chemistry missions can enhance the science data content and quality and may be added with relatively low cost using OAL receiver technology
Aside from, or as an adjunct to, the Decadal Survey missions, GEO could be considered for a multi-mode lidar approach for high value full time regional observations (see previous paper and biblio. On slide 18), also as a hosted payload on communications satellites.

21. Backups

22. A Brief Optical Autocovariance Lidar History
1995 Schwiesow and Mayor, NCAR: Paper describing the use of Optical Autocovariance for Wind Measurement- Coherent Optical Signal Processing for a Doppler Lidar Using a Michelson Interferometer., Coherent Laser Radar Conference (Keystone, CO). OSA Technical Digest Series 19, WA5-1 through WA5-4.
1996 Liu and Kobayashi Fukui U. Japan: defined Mach-Zehnder with 4-channel polarization multiplexing, and a T0 sample, analyzed for Doppler wind measurement. Opt. Rev. V3,
2001 Bruneau, CNRS Analysis of Mach-Zehnder, with 4-channel polarization multiplexing for Doppler Wind Lidar (Discriminator using channel ratios, NOT Autocovariance, wind measurement sensitive to aerosol/molecular backscatter ratio and temerature)
2004 Bruneau, et al: Relative (NOT absolute) wind profiles with a M-Z discriminator (NOT Autocovariance)
2004 Schweisow, Ball Aerospace: Started development at Ball in 2004 with IR&D funds, patent issued 2008.
2006 Grund – built and demonstrated absolute wind measurement with Optical Autocovariance DWL proof of concept based with 3 parallel step interferometer;
2007 Grund and Pierce designed a practical, absolute-referenced, field-widened, multi-l receiver in 2007, built in 2008,9 with IR&D funds. Method and apparatus patent issued 2011.
Grund and Tucker, Ball under NASA IIP: Complete, practical optical autocovariance, field-widened, absolute referenced, DWL built and validation on ground and in air.
2011 Tucker, Delker, Grund, Ball under NASA IIP: Successful OAWL ground validations

23. Space-based OA Performance Modeling – Radiometry with Realistic Components and Atmosphere
LEO Model Parameters:
Wavelength nm, 532 nm
Pulse Energy mJ
Pulse rate Hz
Receiver diameter m (single beam)
LOS angle with vertical
Vector crossing angle
Horizontal resolution* km (500 shots)
System transmission
Alignment error mR average
(NOTE: ~50 mR allowed)
Background bandwidth pm
Orbit altitude km
Vertical resolution km, 250m
2-12 km, 500m
12-20 km, 1 km
Phenomenology CALIPSO model
Volume backscatter cross section at 355 nm (m-1sr-1)
Altitude (km)
Previously approved
Input assumptions for hypothetical performance predictions from space-based lidar
l-scaled validated CALIPSO Backscatter model used. (l-4 molecular, l-1.2 aerosol)
Model calculations validated against short range POC measurements.
Ball Aerospace & Technologies

24. Concept: GEO-OAWL Hardware Components – Confluence of Multiple Recent Technology Developments
Electrically Steerable Flash Lidar (ESFL) –
Subject of Carl Weimer’s current NASA ESTO IIP
(Desdyni focus) (1J/pulse OK, 90X90 independent beamlets OK)
355nm, 0.5 – 1J/pulse, 100 Hz (current tech)
Independently retargetable beams
No momentum compensation
Electronic Beam forming and steering
AOM
Laser
Subject of Ball IRAD development
and current NASA ESTO IIP demonstration
(3D Winds focus)
Patent pending
Patents pending
4-phase
Field-widened
OAWL Receiver
Fixed-pointing
Wide-Field
Receiver
Telescope (~3°X3°)
Subject of Ball IRAD development
for high-sensitivity and resolution flash lidar and low- light passive astrophysical imaging (Intensified Imaging Photon Counting (I2PC) FPA).
New. Top level hypothetical architecture block diagram, no data
4 Photon counting Profiling,Flash Lidar Imaging Arrays
Co-boresighted
camera to geo-locate pixels from topographic outlines
Patent pending
ESFL allows targeting with high spatial resolution and adaptive cloud avoidance

25. Modeled GEOWindSat system performance parameters vs. Calipso (LEO)
Pixel

26. Modeled GEOWindSat Hosted Payload SWaP
Available on communications satellites
<1000
< <460

27. Hurricane Katrina Context, for Example
Eye-wall winds?
Inflow
Shear
Steering
New: see previous slide