Focal Plane Array (Flash) LIDAR€¦ · Focal Plane Array (APD-FPA) Microchannel Plate Detectors...

Focal Plane Array (Flash) LIDAR

Lewis Graham CTO, GeoCue Corporation 9668 Madison Blvd., Suite 202 Madison, AL 35758 USA 01-256-461-8289 lgraham@geocue.com www.geocue.com

SOME INTRODUCTORY THOUGHTS

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Laser Imaging, Detection and Ranging (LIDAR)

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Speed of light is constant, in a vacuum (Albert Einstein – 1905)

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Why LASER? (why not just a flashlight)?

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Spatially Coherent – low beam divergence

Temporally Coherent – short pulses

It’s all about timing … •  Light travels ~3 x 1010 cm in one second. •  Light travels ~30 cm in 1 nanosecond (10-9 sec) •  Light travels 1 cm in ~33.33 picoseconds (10-12 sec)

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A nanosecond is about 1 foot

… and Position … (X, Y, Z)

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GPS error is constant with respect to range

… and Attitude… (Pitch, Yaw, Roll)

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You have to have a good attitude to do proper LIDAR … Attitude errors are

magnified by range

…and mechanicals …

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… and planning …

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Clockwise from Top: Range, Intensity (I), Range modulated by (I)

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Warning! - The following information is full of my supposition and extrapolation – use at your own risk!!

First, some Physics…

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Photon – light particle (Max Plank, 1901)

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•  “particle” of electromagnetic radiation (“light”) •  Speed = 3 x 108 m/s, in a vacuum •  Rest mass = 0 •  Charge = 0 •  Cannot be directly detected

Stimulated Emission (laSEr) (A. Einstein, 1917)

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Billions and Billions….

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There are about 5 x 1014

photons in a single Airborne Laser Scanning pulse

Photoelectric Effect - Detecting (Discovered: Heinrich Hertz – 1887; Explained: A. Einstein – 1905)

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Secondary Ionization - Amplifying (John Townsend – 1897)

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Photomultiplier Tube

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Avalanche Photodiode (APD)

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Electromagnetic Spectrum

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Topo

Bathy

Doping versus λ

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1,064 nm ! Topo

532 nm ! Bathy

FOCAL PLANE ARRAY (FLASH) LIDAR

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Focal Plane Array (Flash) LIDAR

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Array Detector Approaches

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Avalanche Photo Diode Focal Plane Array (APD-FPA)

Microchannel Plate Detectors (MCP-PMT)

Nano electron injection

Avalanche Photo Detectors (APD)

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Courtesy Advanced Scientific Concepts, Inc.

An Avalanche Photo Detector (Focal Plane Array, FPA)

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Linear-mode vs. Geiger-mode •  APDs can be operated in linear-mode or Geiger-mode •  Geiger-mode provides much more sensitivity •  Linear-mode can produce intensity images

1!

10!

100!

M!

Breakdown!0!

Ordinary photodiode!

Linear-mode APD!

Geiger-mode APD!

Response to a photon!

M!1!∞! I(t)!

(Image Credit: D.F Figer.)

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Single Photon Avalanche Detector (SPAD)

PIN Diode APD

ASC DragonEye

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•  Linear mode 128 x 128 InGaAs APD

•  45◦ x 45◦ FOV •  1.5 km range •  Size: 11.2 cm x 13.2 cm x 11.9 cm •  Mass ~ 3 kg •  1570 nm, Class 1 laser •  Repetition - Nominal 5 Hz, up to

30 Hz possible

Avalanche Photo Detector configured in linear mode

Courtesy – Advanced Scientific Concepts, Inc.

LIDAR Video

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Courtesy Advanced Scientific Concepts

Microchannel Plate Detector

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Also referred to as “image intensifiers”, this technology is used in night vision equipment

Sigma Space

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•  Multiple laser beamlets •  Returns from individual beamlets are imaged into a pixelated

detector. •  Each pixel output is input to one channel of a Sigma-built high

resolution (< 100 psec), multi-stop timer to form a 3D image on each pulse. Individual images are mosaiced together by the aircraft motion and an optical scanner.

•  A high speed scanner is synchronized to the laser pulse train and can generate a wide variety of patterns. The transmitter and receiver share a common telescope and scanner.

•  Channel recovery time (detector plus electronics) is only 1.6 nsec (or ~ 24 cm) , compared to 10’s or 100’s of nsec in Single Photon Avalanche Diode (SPAD) systems.

•  System operates in full day light, and can record multiple events per pixel channel per shot.

Parameter Specification Beams 100 Wavelength 532 nm Laser Repetition Rate 25 kHz Lase Pulsewidth 700 psec Laser Output Power 1.5W Pixels/sec 2.5 Millon Eye safety Eye safe by FAA standards Multiple Return Capabillity Yes Pixel Recovery Time 1.6 nsec RMS Range Precision ± 5 cm Scan Patterns linear, conical Scan Width 0 to 40 degrees (selectable) Operational Altitude Range * 6.5 - 10 kft Swath vs AGL** (at maximum scan angle) 1.3 to 2 Km Areal Coverage vs AGL ** (at maximum scan angle and 200 Knots) 400 to 640 Km2 / hr single pass

Mean Point Density 12 to 8 per sq meter, single pass, with 15% reflectivity

Size 19 W x 25 D x 33 H inches Weight 50 lbs Prime Power 555 W

* higher altitude possible, but with lower mean points/m2 density

Sigma Space - HRQLS (High Resolution Quantum Lidar System) Specifications:

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mileskm

3060

SPL 3D mapping of Garrett County, MD, 1700 Sq Km 50% overlap, 12 hrs total (including ferry and turns)

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Common Issues •  Jitter •  Dark Current •  Ambient contributions (stray light) •  Stochastic nature of the avalanche •  Recovery time (particularly in Geiger mode)

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A different approach… Nano-electron injection

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Why do we care?

•  Higher point collection speeds – parallel processing as compared to single beam systems

•  Framing geometry – higher achievable accuracy •  Lower complexity systems design •  Geiger mode offers some very interesting ‘imaging’

scenarios of extremely low return energy collections – Very high altitude – Deep vegetation penetration – think distribution wires!!

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Why do we care (cont.) •  sUAS deployed LIDAR •  Integrated LIDAR/Imaging sensors – true 3D

cameras on a chip!

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Commercial Players… •  Advanced Scientific Concepts, Inc. •  Princeton Lightwave

– Commercialization of the MIT Lincoln Labs work •  Sigma Space Corporation •  Spectrolab (Boeing)

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Economic Driver?

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Special Thanks to: •  Advanced Scientific Concepts, Inc.

– www.advancedscientificconcepts.com •  Sigma Space Corporation

– www.sigmaspace.com •  Northwestern University

– www.northwestern.edu

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Thank You!

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