This document describes the development of an airborne lidar instrument called A-LISTS to demonstrate technologies for a proposed spaceborne lidar mission called LIST. LIST aims to map global topography at 5m resolution to study Earth's surface and changes over time. A-LISTS will test a multi-beam laser transmitter, high sensitivity detectors, and data processing to achieve LIST measurement capabilities from an aircraft. Its first flight in September 2011 will collect lidar data over various terrain to evaluate performance. Key challenges for LIST that A-LISTS helps address include detecting ground returns through vegetation canopies and developing efficient, lightweight instruments.

1. Sixteen Channel, Non-Scanning Airborne Lidar Surface Topography (LIST) Simulator A.W. Yu, M.A. Krainak, D.J. Harding, J.B. Abshire, X. Sun, J.F. Cavanaugh, S.R. Valett, L. Ramos-Izquierdo, T. Winkert, C. Kirchner, M. Plants, T. Filemyr, B. Kamamia and W. Hasselbrack NASA Goddard Space Flight Center, Greenbelt, MD 20771 Paper: FR2.T03.3 IGARSS 2011, Vancouver, Canada 29 JULY 2011

2. Outline Introduction LIST Science Objectives & Requirements Lidar Measurement Approach & Performance Analysis Airborne Instrument Development Summary

3. Lidar surface topography (LIST) Science objectives & requirements

5. climate/tectonics/erosion interactions

7. disturbance & response

8. habitat and biodiversity

9. wild-fire fuel loads

11. ice flow and dynamics

13. snow depth

15. 5 m spatial resolution (i.e., pixel size)

16. ≤ 10 cm vertical precision per 5 m pixel for flat surfaces

17. ≤ 20 cm absolute vertical accuracy per 5 m pixel for flat surfaces

18. Acquire images of vegetation height and vertical structure

19. 1 m vertical resolution per 25 m x 25 m area

20. Complete one-time global mapping in 3 years

22. Monthly for water storage and natural hazard topographic change

24. Measurement wavelength with high surface reflectance, low atmosphere loss and good receiver QE

25. Highest receiver sensitivity – single photon detection

26. Wide receiver dynamic range – linear photon detection

30. Microchip Yb:YAG Oscillator 5.70” 4.23” 2.28” Beam Quality: M2x = 1.16 M2y = 1.21 Energy: 107 µJ Energy variation is ~0.1% (~3 hr) PRF: 2 kHz Pulsewidth: 947 ± 25 ps Wavelength: 1030.140 ± 0.002 nm Linewidth: <16 pm

32. Yb:YAG gain medium - 1030 nm

33. ~1 ns FWHM, ~100 µJ, 2-10 kHz

35. Goal of 1.6 mJ @ 10 kHzMaster Oscillator - Microchip Laser

37. 10-20% QE, single photon sensitivity, 1 nsec analog response

39. >75% QE @ 1 µm

40. Requires full MOPA at 100 µJ/beam1030 nm Photon Sensitive Detectors APD anode array

41. IPD vs InGaAs APD GHz photoreceiver comparison ALIST Swath Mapper Performance with I2E APD receiver. ALISTS Swath Mapper Performance with IPD receiver.

42. Space and Airborne Measurement Comparison Both use micropulse lidar with waveform capturing and analysis detection scheme First flight – Sept 2011

43. Airborne list simulator (A-lists) Development

44. A-LISTS Layout Rx Subsystem FIBER OPTIC BUNDLE Laser Telescope Keyboard/Mon Amplifiers BX PWR STRIP Video Recorder TIME CODE VIDEO Detector PS Support Frame MLA Pulse Gen+GPS Att. Align PWR STRIP Laser/TEC Ctl + Amp PS+ Chiller A/C Window DAS Lear Rack 2 Lear Rack 1

45. Boresight Alignment of the A-LISTS Transceiver Ground Testing Configuration 4x4 Fiber Bundle from Telescope Flight Configuration Start pulse from Tx Alignment of 16 channel Tx beams to 16 pixel IPA array with Autocollimator Laser output 7” Dia Rx Telescope 4x4 Fiber Bundle to Detector Array Rx Subsystem - IPD Output to 16 channel digitizer Laser Transmitter - [using pair of microlens arrays to generate a 4x4 pattern (patent pending)] A-LISTS Transceiver Enclosure on LearJet Fiber start pulse pickoff to receiver box Microlens arrays

46. IIP Airborne Footprint Velocity vector Yaw rotation of 14.5° yields uniformly spaced spots with 5 m horizontal spacing Geolocation accuracy of 1 m to assign return to correct 5 m pixel on ground 75 m Altitude = 10 km: Detector FOV = 7 m (0.7 mrad) Laser Spot = 5 m (0.5 mrad) Laser Spot Spacing = 20 m (2 mrad)

47. Single channel test results

48. Single Channel Ranging Demonstration- Test Setup Cell Tower with Hard Target (1.5 km one way) Rx Telescope Intevac Single Element IPD Tx Telescope Multimode Fiber to Tx Telescope Start Pulse Detector GLAS Flight Spare Detector RSAS µchip Laser

49. Tower Target Board Returns Si APD output, single shot Target Board Return Start pulse leak through IPD output at 1/30 pulse energy, 7 shots overlaid Target Board Return HPMT dark counts and solar background counts Black: Averaged

50. Tower Target Board Return (Si APD & IPD) Si APD output pulse waveforms from the target board(~700 photons/pulse, 4ns FWHM) APD output (V) Sample number (at 0.2ns/sample) Laser shot number IPD output pulse waveforms from the steel tower structure IPD output pulse waveforms from the target board (~20 photons/pulse, 1ns FWHM) Back of the tower Front of the tower 20 ns (3m) IPD output (V) IPD output (V) Laser shot number Laser shot number Sample number (at 0.2ns/sample) Sample number (at 0.2ns/sample)

52. Smithsonian Environmental Research Center (SERC), Edgewater, MD (ICESat-2 study site)

53. Very well characterized canopy structure from ground measurements

54. Prior data collections: LVIS, Sigma Micropulse, Commercial, SIMPL, Ball ESFL

55. Closed deciduous canopy, rugged topography

56. Liberty Reservoir, Baltimore County, MD

57. Prior data collections: LVIS, Commercial

58. Open coniferous canopy, flat topography

59. Pine Barrens, NJ (ICESat-2 study site)

60. Prior data collections: Sigma Micropulse, Commercial, SIMPL

61. Diverse, managed coniferous canopy, flat topography

62. Huron National Forest, MI

63. Prior data collections: SIMPL

64. Non-vegetated, rough topography

65. Boulder Field, Hickory Run State Park, MD

66. Prior data collections: SLICER, Commercial

67. Bare to sparse vegetation, flat topography

68. Assateague Island National Seashore, MD

69. Prior data collections: ATM

70. Urban

71. Ocean City, MD

72. Prior data collections: ATMSERC, MD

74. Will demonstrate LIST-type measurements over a variety of surface types, including those of vegetation canopy and substructures.

75. Data system – requires multi-channel, high sampling rate and bandwidth digitizers with minimum of 8-bit resolution and high data transfer rate.

77. Raytheon Vision Systems

78. Intevac

79. Spectrolabsfor their technical support