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  1. 1. Sixteen Channel, Non-Scanning Airborne Lidar Surface Topography (LIST) Simulator<br />A.W. Yu, M.A. Krainak, D.J. Harding, J.B. Abshire, X. Sun,<br />J.F. Cavanaugh, S.R. Valett, L. Ramos-Izquierdo, T. Winkert,<br />C. Kirchner, M. Plants, T. Filemyr, B. Kamamia and W. Hasselbrack <br />NASA Goddard Space Flight Center,<br />Greenbelt, MD 20771<br />Paper: FR2.T03.3 <br />IGARSS 2011, Vancouver, Canada<br />29 JULY 2011<br />
  2. 2. Outline<br />Introduction<br />LIST Science Objectives & Requirements<br />Lidar Measurement Approach & Performance Analysis<br />Airborne Instrument Development<br />Summary<br />
  3. 3. Lidar surface topography (LIST) Science objectives & requirements<br />
  4. 4. LIST Science Objectives<br />LIST will provide high-resolution elevation images of the Earth’s solid surface & its overlying covers of vegetation, water, snow, ice and manmade structures.<br />Provides data fundamental to understanding, modeling and predicting interactions between the Solid Earth, hydrosphere, biosphere, cryosphere and atmosphere.<br />Solid Earth<br /><ul><li>landscape evolution
  5. 5. climate/tectonics/erosion interactions
  6. 6. earthquake, volcano, landslide and coastal</li></ul> hazards<br />Vegetation Structure<br /><ul><li>carbon storage
  7. 7. disturbance & response
  8. 8. habitat and biodiversity
  9. 9. wild-fire fuel loads
  10. 10. slope stabilization</li></ul>Cryosphere<br /><ul><li>ice sheet, ice cap, glacier elevation change
  11. 11. ice flow and dynamics
  12. 12. sea ice cover & thickness</li></ul>Water Cycle<br /><ul><li>water storage
  13. 13. snow depth
  14. 14. river discharge</li></li></ul><li>LIST Measurement Requirements<br /><ul><li>Acquire elevation images of land topography, including where covered by vegetation, and inland water bodies, ice sheets, glaciers and snow cover
  15. 15. 5 m spatial resolution (i.e., pixel size)
  16. 16. ≤ 10 cm vertical precision per 5 m pixel for flat surfaces
  17. 17. ≤ 20 cm absolute vertical accuracy per 5 m pixel for flat surfaces
  18. 18. Acquire images of vegetation height and vertical structure
  19. 19. 1 m vertical resolution per 25 m x 25 m area
  20. 20. Complete one-time global mapping in 3 years
  21. 21. Implies a 5 km or wider swath to build up coverage</li></ul>during clear sky conditions<br /><ul><li>Repeat mapping for change monitoring in selected areas
  22. 22. Monthly for water storage and natural hazard topographic change
  23. 23. Seasonally for ice sheet, sea ice and vegetation structure change</li></li></ul><li>LIST - Challenges for a Space Lidar<br />Complete mapping of the entire Earth in 3 years with 5-m spatial resolution <br />> 5 km Swath with 1000 parallel profiling lines (or channels) <br />Detecting ground echoes through tree canopies (2% opening) under clear sky conditions (~70% one way transmission)<br />Alignment of 1000 transmitters and receiver optics<br />1000 channel data acquisition, processing, and storage<br />Resource Goals: < 10 kW peak electrical power (or 10 W per channel) and <700 kg mass<br />Need approach with high “measurement efficiency:” <br /><ul><li>Highest laser ‘wall-plug efficiency’
  24. 24. Measurement wavelength with high surface reflectance, low atmosphere loss and good receiver QE
  25. 25. Highest receiver sensitivity – single photon detection
  26. 26. Wide receiver dynamic range – linear photon detection
  27. 27. Practical receiver signal processing & hardware implementation</li></li></ul><li>Lidar Measurement Approach & Performance Analysis<br />
  28. 28. Lidar Measurement Approaches - Single Photon Detection and Averaging<br />*<br /><ul><li>SIMPL – Slope Imaging Multi-polarization Photon-counting Lidar (D. Harding, PI, NASA /GSFC)
  29. 29. IGARSS 2011, Paper TH1.T10.4: Harding,, “Airborne Polarimetric, Two-Color Laser Altimeter Measurements of Lake Ice Cover: A Pathfinder for NASA ICESat-2 Spaceflight Mission”</li></li></ul><li>LIST with 1030 nm PMT Detection - Space- NIR PMT Single Photon Sensitivity<br />Approach:<br />Photon sensitive detection <br />PMT -> analog digitizer<br />Multiple laser pulse histogramming<br />NIR-PMT detector: 10% QE<br />Laser Illumination:<br />Laser fire rate along track: 10 kHz<br />Laser firings/pixel: 7 <br />Laser energy/pulse: 50 µJ<br />Ave Laser Power/track: 0.5 W <br />Ave Prime Power/track (assuming 10% efficient): 5 W<br />Detection Probability:<br />>90% after averaging received signal over 7 laser shots <br />Range jitter:<br />Vertical offset - laser pulse range spread<br />Floor set - digitizer rate (1.5 GHz)<br />Desired<br /><ul><li>NIR PMT detection improves receiver sensitivity by x7 </li></ul>Model From: Harding IIP-04<br />
  30. 30. Microchip Yb:YAG Oscillator<br />5.70”<br />4.23”<br />2.28”<br />Beam Quality: M2x = 1.16<br /> M2y = 1.21<br />Energy: 107 µJ<br />Energy variation is ~0.1% (~3 hr)<br />PRF: 2 kHz<br />Pulsewidth: 947 ± 25 ps<br />Wavelength: 1030.140 ± 0.002 nm<br />Linewidth: <16 pm<br />
  31. 31. MOPA Laser Transmitter for IIP <br />Laser Architecture: Master Oscillator Power Amplifier (MOPA)<br /><ul><li>Master Oscillator (MO): Microchip lasers
  32. 32. Yb:YAG gain medium - 1030 nm
  33. 33. ~1 ns FWHM, ~100 µJ, 2-10 kHz
  34. 34. capable of meeting the airborne requirements</li></ul>of 16 beams, 5 µJ/beam with Intevac IPD<br /><ul><li>MOPA: Microchip laser seeding Power Amplifier (PA): Planar waveguide amplifier
  35. 35. Goal of 1.6 mJ @ 10 kHz</li></ul>Master Oscillator - Microchip Laser<br />
  36. 36. Candidate Detector Arrays –<br />1. Intevac Multi-anode Intensified Photodiode (IPD)<br /><ul><li>InGaAsP photocathode – GaAs APD anode
  37. 37. 10-20% QE, single photon sensitivity, 1 nsec analog response
  38. 38. Requires only the MO at 5 µJ/beam</li></ul>2. SpectrolabInAlAsP APD detectors(ESTO ACT-Krainak/PI)<br /><ul><li>16 individual fiber coupled APDs
  39. 39. >75% QE @ 1 µm
  40. 40. Requires full MOPA at 100 µJ/beam</li></ul>1030 nm Photon Sensitive Detectors<br />APD anode array<br />
  41. 41. IPD vs InGaAs APD GHz photoreceiver comparison<br />ALIST Swath Mapper Performance with I2E APD receiver. <br />ALISTS Swath Mapper Performance with IPD receiver. <br />
  42. 42. Space and Airborne Measurement Comparison<br />Both use micropulse lidar with waveform capturing and analysis detection scheme<br />First flight – Sept 2011<br />
  43. 43. Airborne list simulator (A-lists) Development<br />
  44. 44. A-LISTS Layout<br />Rx Subsystem<br />FIBER OPTIC BUNDLE<br />Laser<br />Telescope<br />Keyboard/Mon<br />Amplifiers<br />BX<br />PWR STRIP<br />Video Recorder<br />TIME CODE VIDEO<br />Detector PS<br />Support<br />Frame<br />MLA<br />Pulse Gen+GPS<br />Att.<br />Align<br />PWR STRIP<br />Laser/TEC Ctl + Amp PS+ Chiller<br />A/C Window<br />DAS<br />Lear Rack 2<br />Lear Rack 1<br />
  45. 45. Boresight Alignment of the A-LISTS Transceiver <br />Ground Testing Configuration<br />4x4 Fiber Bundle from Telescope<br />Flight Configuration<br />Start pulse from Tx<br />Alignment of 16 channel Tx beams to 16 pixel IPA array with Autocollimator<br />Laser output<br />7” Dia Rx Telescope<br />4x4 Fiber Bundle to Detector Array<br />Rx Subsystem - IPD Output to 16 channel digitizer <br />Laser Transmitter - [using pair of microlens arrays to generate a 4x4 pattern (patent pending)]<br />A-LISTS Transceiver Enclosure on LearJet<br />Fiber start pulse pickoff to receiver box<br />Microlens arrays<br />
  46. 46. IIP Airborne Footprint<br />Velocity vector<br />Yaw rotation of 14.5° yields uniformly spaced spots with 5 m horizontal spacing<br />Geolocation accuracy of 1 m to assign return to correct 5 m pixel on ground<br />75 m<br />Altitude = 10 km:<br />Detector FOV = 7 m (0.7 mrad)<br />Laser Spot = 5 m (0.5 mrad)<br />Laser Spot Spacing = 20 m (2 mrad) <br />
  47. 47. Single channel test results<br />
  48. 48. Single Channel Ranging Demonstration- Test Setup<br />Cell Tower with Hard Target <br />(1.5 km one way)<br />Rx Telescope<br />Intevac Single Element IPD<br />Tx Telescope<br />Multimode Fiber to Tx Telescope<br />Start Pulse Detector<br />GLAS Flight Spare Detector<br />RSAS µchip Laser<br />
  49. 49. Tower Target Board Returns<br />Si APD output, single shot<br />Target Board Return<br />Start pulse leak through<br />IPD output at 1/30 pulse energy, 7 shots overlaid<br />Target Board Return<br />HPMT dark counts and solar background counts<br />Black: Averaged<br />
  50. 50. Tower Target Board Return (Si APD & IPD)<br />Si APD output pulse waveforms from the target board(~700 photons/pulse, 4ns FWHM)<br />APD output (V)<br />Sample number (at 0.2ns/sample)<br />Laser shot number <br />IPD output pulse waveforms from the steel tower structure<br />IPD output pulse waveforms from the target board<br />(~20 photons/pulse, 1ns FWHM)<br />Back of the tower<br />Front of the tower<br />20 ns (3m)<br />IPD output (V)<br />IPD output (V)<br />Laser shot number <br />Laser shot number <br />Sample number (at 0.2ns/sample)<br />Sample number (at 0.2ns/sample)<br />
  51. 51. 2011 Target Sites for Flight Demonstration<br /><ul><li>Closed deciduous canopy, undulating topography
  52. 52. Smithsonian Environmental Research Center (SERC), Edgewater, MD (ICESat-2 study site)
  53. 53. Very well characterized canopy structure from ground measurements
  54. 54. Prior data collections: LVIS, Sigma Micropulse, Commercial, SIMPL, Ball ESFL
  55. 55. Closed deciduous canopy, rugged topography
  56. 56. Liberty Reservoir, Baltimore County, MD
  57. 57. Prior data collections: LVIS, Commercial
  58. 58. Open coniferous canopy, flat topography
  59. 59. Pine Barrens, NJ (ICESat-2 study site)
  60. 60. Prior data collections: Sigma Micropulse, Commercial, SIMPL
  61. 61. Diverse, managed coniferous canopy, flat topography
  62. 62. Huron National Forest, MI
  63. 63. Prior data collections: SIMPL
  64. 64. Non-vegetated, rough topography
  65. 65. Boulder Field, Hickory Run State Park, MD
  66. 66. Prior data collections: SLICER, Commercial
  67. 67. Bare to sparse vegetation, flat topography
  68. 68. Assateague Island National Seashore, MD
  69. 69. Prior data collections: ATM
  70. 70. Urban
  71. 71. Ocean City, MD
  72. 72. Prior data collections: ATM</li></ul>SERC, MD<br />
  73. 73. Summary<br /><ul><li>Develop key technologies and an airborne instrument to meet the LIST mission requirements and provide scalability study for spaceborne mission.</li></ul>High efficiency, short pulse (< 1 ns) multi-beam laser transmitters;<br />Higher sensitivity array detectors, waveform capturing;<br />Similar spatial resolution (spot diameters) as LIST;<br />to collect LIST like signal to study data reduction technique. <br /><ul><li>Advanced TRL of critical subsystems (Laser & Detector) on airborne platform.
  74. 74. Will demonstrate LIST-type measurements over a variety of surface types, including those of vegetation canopy and substructures.
  75. 75. Data system – requires multi-channel, high sampling rate and bandwidth digitizers with minimum of 8-bit resolution and high data transfer rate.
  76. 76. First flight – September 2011</li></li></ul><li>Acknowledgement<br />The authors would like to thank NASA ESTO for supporting the Swath Mapper IIP and the detector development effort from the Advanced Component Technology (ACT) program.<br />The authors would also like to thank<br /><ul><li>Raytheon Space and Airborne Systems
  77. 77. Raytheon Vision Systems
  78. 78. Intevac
  79. 79. Spectrolabs</li></ul>for their technical support<br />