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This section contains the title page, introduction to the series, the table of contents, and the flossary of symbols and acronyms.

Library of Congress Preassigned Control Number:

2015931195

for

Field Guide to Lidar (ISBN 9781628416541).

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Printed in the United States of America.

First printing

Introduction to the Series

Welcome to the SPIE Field Guides—a series of publications written directly for the practicing engineer or scientist. Many textbooks and professional reference books cover optical principles and techniques in depth. The aim of the SPIE Field Guides is to distill this information, providing readers with a handy desk or briefcase reference that provides basic, essential information about optical principles, techniques, or phenomena, including definitions and descriptions, key equations, illustrations, application examples, design considerations, and additional resources. A significant effort will be made to provide a consistent notation and style between volumes in the series.

Each SPIE Field Guide addresses a major field of optical science and technology. The concept of these Field Guides is a format-intensive presentation based on figures and equations supplemented by concise explanations. In most cases, this modular approach places a single topic on a page, and provides full coverage of that topic on that page. Highlights, insights, and rules of thumb are displayed in sidebars to the main text. The appendices at the end of each Field Guide provide additional information such as related material outside the main scope of the volume, key mathematical relationships, and alternative methods. While complete in their coverage, the concise presentation may not be appropriate for those new to the field.

The SPIE Field Guides are intended to be living documents. The modular page-based presentation format allows them to be updated and expanded. We are interested in your suggestions for new Field Guide topics as well as what material should be added to an individual volume to make these Field Guides more useful to you. Please contact us at fieldguides@SPIE.org.

John E. Greivenkamp, Series Editor

College of Optical Sciences

The University of Arizona

The Field Guide Series

Keep information at your fingertips with the SPIE Field Guides:
  • Adaptive Optics, Second Edition, Robert Tyson & Benjamin Frazier

  • Atmospheric Optics, Larry Andrews

  • Binoculars and Scopes, Paul Yoder, Jr. & Daniel Vukobratovich

  • Diffractive Optics, Yakov Soskind

  • Digital Micro-Optics, Bernard Kress

  • Displacement Measuring Interferometry, Jonathan D. Ellis

  • Fiber Optic Sensors, William Spillman, Jr. & Eric Udd

  • Geometrical Optics, John Greivenkamp

  • Holography, Pierre-Alexandre Blanche

  • Illumination, Angelo Arecchi, Tahar Messadi, & John Koshel

  • Image Processing, Khan M. Iftekharuddin & Abdul Awwal

  • Infrared Systems, Detectors, and FPAs, 2nd Edition, Arnold Daniels

  • Interferometric Optical Testing, Eric Goodwin & Jim Wyant

  • Laser Pulse Generation, Rüdiger Paschotta

  • Lasers, Rüdiger Paschotta

  • Lens Design, Julie Bentley & Craig Olson

  • Linear Systems in Optics, J. Scott Tyo & Andrey Alenin

  • Microscopy, Tomasz Tkaczyk

  • Nonlinear Optics, Peter Powers

  • Optical Fabrication, Ray Williamson

  • Optical Fiber Technology, Rüdiger Paschotta

  • Optical Lithography, Chris Mack

  • Optical Thin Films, Ronald Willey

  • Optomechanical Design and Analysis, Katie Schwertz & James Burge

  • Physical Optics, Daniel Smith

  • Polarization, Edward Collett

  • Probability, Random Processes, and Random Data Analysis, Larry C. Andrews & Ronald L. Phillips

  • Radiometry, Barbara Grant

  • Special Functions for Engineers, Larry Andrews

  • Spectroscopy, David Ball

  • Terahertz Sources, Detectors, and Optics, Créidhe O'Sullivan & J. Anthony Murphy

  • Visual and Ophthalmic Optics, Jim Schwiegerling

Field Guide to Lidar

This Field Guide covers active electro-optical sensing, in which a sensor sends out a laser pulse and then measures the parameters of the return signal. Various groups refer to this type of sensor as a ladar, lidar, LIDAR, LADAR, or laser radar. For simplicity, only the term lidar is used throughout this book.

The book is presented from the perspective of a lidar engineer. It covers a wide breadth, from simple 2D direct-detection lidars to multiple subaperture synthetic aperture lidars. It also covers a broad range of objects to be viewed, and distances from which to view the objects. Lasers and modulation are discussed in the context of their use in lidars. Other topics covered include receivers, apertures, and atmospheric effects in the context of lidar use and design.

All lidars will be limited by the media between the lidar and the target, but atmospheric compensation techniques can often mitigate this limitation. These limitations and compensation approaches are presented. Many types of lidars are included along with appropriate data processing techniques. The lidar range equation in its many variations is discussed along with receiver noise issues that determine how much signal must be received to detect an object.

This Field Guide is a handy reference to quickly access information on any aspect of lidars. It will be useful to students and lidar scientists or engineers who need an occasional reminder of the correct approaches or equations to use in certain applications. It will also be useful to systems engineers gaining a perspective on this rapidly growing technology.

Paul McManamon

March 2015

Table of Contents

Glossary of Symbols and Acronyms x

Introduction 1

Introduction 1

Terms for Active Electro-optic Sensing 2

Types of Lidars 3

Lidars for Surface-Scattering (Hard) Targets 4

Lidars for Volume-Scattering (Soft) Targets 5

History of Lidar 6

Lidar Detection Modes 7

Spatial Coherence 8

Temporal Coherence 9

Eye Safety Considerations 10

Laser Safety Categories 11

Monostatic versus Bistatic Lidar 12

Transmit/Receive Isolation 13

Lidar Range Equation 14

Lidar Range Equation 14

Lidar Cross Section 15

Cross Section of a Corner Cube 16

Speckle 17

Atmospheric Absorption 18

Atmospheric Scattering 19

Atmospheric Turbulence 20

Aero-optical Effects on Lidar 21

Extended (Deep) Turbulence 22

Laser Power for Lidar 23

Lidar Signal-to-Noise Ratio 24

Direct Detection Signal-to-Noise Ratio 25

Noise Probability Density Functions 26

Thermal Noise 27

Shot Noise 28

The Sun as Background Noise 29

Dark Current, 1/f, and Excess Noise 30

Avalanche Photodiodes and Direct Detection 31

Number of Photons Required for a GMAPD Lidar Camera 32

Heterodyne Detection 33

Temporal Heterodyne Detection 34

Heterodyne Mixing Efficiency 35

Quadrature Detection 36

Carrier-to-Noise Ratio for Temporal

Heterodyne Detection 37

Spatial Heterodyne Detection/Digital Holography 38

SNR for Spatial Heterodyne Detection 39

Types of Lidars 40

1D Range-Only Lidar 40

Tomographic Imaging Lidar 41

Range-Gated Active Imaging (2D Lidar) 42

3D Scanning Lidar 43

3D Flash Imaging 44

Geiger-Mode APD Flash Lidar 45

Linear-Mode APD Flash Lidar 46

Polarization-based Flash Lidar using Framing Cameras 47

Laser Vibration Detection 48

Synthetic Aperture Lidar 49

Inverse Synthetic Aperture Lidar 50

Range Doppler Imaging Lidar 51

Laser-Induced Breakdown Spectroscopy 52

Laser-Induced Fluorescence Lidar 53

Active Multispectral Lidar 54

Lidars Using Polarization as a Discriminant 55

Speckle Imaging Lidar 56

Phased Array of Phased-Array Imaging Lidar 57

Multiple Subapertures on Receive for Lidar 58

Multiple-Input, Multiple-Output Lidar 59

Methods of Phasing MIMO Lidars 60

Lidar Sources and Modulations 61

Lidar Sources and Modulations 61

Laser Resonators 62

Three-Level and Four-Level Lasers 63

Bulk Solid State Lasers for Lidar 64

Fiber Lasers for Lidar 65

Higher-Peak-Power Waveguide Lasers for Lidar 66

Diode Lasers for Lidar 67

Quantum Cascade Lasers for Lidar 68

Laser Pumping Considerations 69

Nonlinear Devices to Change the Lidar Wavelength 70

Q-Switched Lasers for Lidar 71

Pockels Cells 72

Mode-Locked Lasers for Lidar 73

Laser Seeding for Lidar 74

Laser Amplifiers for Lidar 75

Multiple Coherent Laser Transmitters 76

Laser Waveforms for Lidar 77

Polypulse Laser Waveforms 78

Linear Frequency Modulation for Lidar 79

Pseudo-random-Coded Lidar 80

RF Modulation of a Direct Detection Lidar 81

Lidar Receivers 82

Linear-Mode APD Arrays for Lidar 82

Geiger-Mode APD Arrays for Lidar 83

Receivers for Coherent Lidars 84

Acousto-optic Frequency Shifting 85

Long-Frame-Time Framing Detectors for Lidar 86

Gated Framing Cameras for 2D Lidar Imaging 87

Lidar Image Stabilization 88

Range Resolution of Lidar 89

Velocity Resolution of Lidar 90

Unambiguous Range 91

Point Spread Function 92

Beam Steering for Lidars 93

Gimbals for Use with Lidar 93

Fast-Steering Mirrors 94

Risley Prisms and Gratings 95

Rotating Polygonal Mirrors 96

Modulo 2π Beam Steering 97

Largest Steering Angle for an Optical Phased Array 98

Liquid Crystal Optical Phased Arrays 99

LC Fringing-Field Effect on Steering Efficiency 100

Reduction in Steering Efficiency Due to Quantization 101

Chip-Scale Optical Phased Arrays 102

MEMS Beam Steering for Lidar 103

Electrowetting Beam Steering for Lidar 104

Steerable Electro-evanescent Optical Refractors 105

Electro-optical Effects 106

Polarization Birefringent Grating Beam Steering 107

Step Angle Steering with LC Polarization Gratings 108

Multiple-Stage LCPGs 109

Lenslet-based Beam Steering 110

Electronically Written Lenslets 111

Mixed-Lenslet Arrays 112

Holographic Gratings for Beam Steering 113

Geometrical Optics 114

Lidar Processing 115

Inertial Measurement Units 115

Microscanning of Lidar Images for Improved Sampling 116

Range Measurement Processing 117

Nyquist Sampling a Range Profile 118

Threshold, Leading Edge, and Peak Detectors 119

Range Resolution, Precision, and Accuracy 120

Fourier Transforms 121

Developing 3D Maps from Lidar 122

3D Metrics for Lidar Images 123

Multiple-Subaperture Spatial Heterodyne

Processing 124

Definitions of Lidar Data Processing Stages 125

Processing Laser Vibrometry Data 126

Target Classification Using Lidar 127

Equation Summary 128

Figure Sources 138

Bibliography 141

Index 143

Glossary of Symbols and Acronyms

a

amplitude of the (super) Gaussian

A

length of one side of a tetrahedral

Aillum

area illuminated by the transmitter

AO

acousto-optic

AOM

acousto-optic modulator

Ap

area of the pixel at the target location

APD

avalanche photodiode

APS

active-pixel sensor

Arec

area of the receiver aperture

b

zero position, or offset, of the (super) Gaussian beam

B

bandwidth

c

Gaussian, or super-Gaussian, beam width

c

speed of light

cw

continuous wave

Cl

coherence length

CCD

charge-coupled device

CDMA

code-division multiple access

CMOS

complementary metal-oxide semiconductor

CNR

carrier-to-noise ratio

d

cross-range resolution

d

required lens thickness

d

width of the individual radiator or receiver

D

aperture diameter

DAiry

diameter out to the zeros of the diffraction-limited spot at the focus for a circular aperture

DAS

detector angular subtense

DFLC

dual-frequency liquid crystal

DIAL

differential absorption lidar

DM

deformable mirror

DOP

degree of polarization

e

charge on an electron

E

energy at range

E0

initial energy before traveling through the atmosphere

EBAPS®

electron-bombarded active-pixel sensor

EBS

electron-bombarded semiconductor

Ein

input electric field into a Jones matrix

ELO

local oscillator field

EM

electromagnetic

EO

electro-optic

Eout

input electric field into a Jones matrix

Ep

energy in a photon

ER

received energy per pulse

Esig

returned signal field

ET

transmitted energy per pulse

Eth

thermal energy

Exin

x portion of the input electric field

Exout

x portion of the output electric field

Eyin

y portion of the input electric field

Eyout

y portion of the output electric field

f

focal length of the lens

f/#

F-number of an optical element

fl

focal length of a lenslet

f(x)

Gaussian or super-Gaussian beam profile in one dimension

F

excess noise factor associated with the preamplifier gain

FDMA

frequency-division multiple access

FFT

fast Fourier transform

FLC

ferroelectric liquid crystal

FLIR

forward-looking infrared (camera)

FM

frequency modulated

FOV

field of view

FPA

focal plane array

FSM

fast-steering mirror

G

avalanche gain

GIQE

general image quality equation

GMAPD

Geiger-mode avalanche photodiode

GML

Geiger-mode lidar

h

Planck’s constant

HWP

half-wave plate

ibk

background current

idk

dark current

in

noise current in the detector

is

signal current in the detector

ishotLO

shot noise from the local oscillator

ishot,sig

shot noise from the signal

ith

thermal noise current

I

intensity of the beat between the local oscillator and the return signal

Idkb

bulk dark current

Idks

surface dark current

IF

intermediate frequency

IMU

inertial measurement unit

IR

infrared

k

effective elastic constant

k

number of photons in M events

k

Boltzmann constant

L

distance flown

L

length of the laser cavity

LCPG

liquid crystal polarization grating

LFM

linear frequency modulation

LIBS

laser-induced breakdown spectroscopy

LIF

laser-induced fluorescence

LIMAR

laser imaging and ranging

LMAPD

linear-mode avalanche photodiode

LO

laser oscillator

LWIR

long-wave infrared

Lλ

radiance per wavelength

M

number of events

M2

measure of the spatial coherence of a laser beam. An M2 of 1 means it is diffraction limited.

MEMS

micro-electro-mechanical system

MIMO

multiple input, multiple output

MO

master oscillator

MPE

maximum permissible exposure

MWIR

midwave infrared

n

index of refraction

n

number of individual radiators or receivers

nm

diffraction efficiency of the mth order

N

number of photons per pixel received during a measurement time

N

super-Gaussian beam number. Higher numbers mean a more flat-topped beam shape.

NA

numerical aperture

NEPh

noise-equivalent photons

NIIRS

National Imagery Interpretability Rating Scale

NIR

near infrared

OPA

optical parametric amplifier

OPA

optical phased array

OPD

optical path difference

OPO

optical parametric oscillator

p(k)

Gaussian probability distribution

P

number of modes

PAPA

phased array of phased arrays

PLO

local oscillator power

PPLN

periodically poled lithium niobate

PS

signal power received

PSD

power spectral density

PSF

point spread function

PT

power transmitted

Pthdbm

thermal noise power

q

Poisson distribution probability

q

number of discrete steps

QCL

quantum cascade laser

QWP

quarter-wave plate

r0

Fried parameter

R

range to the target

detector responsivity

RF

radio frequency

RL

load resistance

ROIC

readout integrated circuit

Runambig

unambiguous range

S′3 = S3/S0

normalized Stokes parameter corresponding to ellipticity of incident light

SNR

signal-to-noise ratio

SPGD

stochastic parallel gradient descent

SS

solid state

SWIR

short-wave infrared

t

cell thickness

tlens(waz, wel)

lens phase profile

T

temperature

T

time separation between pulses

TDMA

time-division multiple access

Tm

time period over which a measurement is made

v

velocity of the lidar with respect to the surrounding air

V

platform velocity

V

relative velocity between the lidar and the target

V

voltage on an electrode

VCSEL

vertical-cavity surface-emitting laser

Vt

threshold voltage

wel2+wel2

beam width in azimuth and elevation for a Gaussian profile

β

angle between the slow axis of the half-wave plate and the x axis in the Jones matrix

β

atmospheric decay constant

γ

viscosity

Δf

change in frequency due to the Doppler shift

Δn

change in index of refraction

Δz

surface roughness

ΔR

range resolution

Δt

mode-locked pulse width

ΔV

velocity resolution

Δx

lenslet motion

Δϑ

angular resolution for a synthetic aperture lidar

Δλ

linewidth of the laser in wavelength

Δϕ

angular motion used in an inverse synthetic aperture lidar image

η

steering efficiency due to quantization error

ηatm

transmission of the atmosphere in one direction

ηh

heterodyne mixing efficiency

ηsys

total transmission of the lidar system, both in and out

θ

angular motion created by the lenslet

θmax

maximum steering angle

ϑ

angle of deflection for an AO modulator

ϑ

full beam width, half maximum diffraction limit

λ

wavelength

λi

wavelength of the idler laser

λp

wavelength of the pump laser

λs

wavelength of the signal laser

Λ

acousto-optical wavelength

Λ

width between resets

ΛF

width of the flyback region

ν

carrier frequency of light (ω = 2πν)

ρ

radius of the microlens

ρt

reflectance of the area

σ

cross section

τ0

coherence time

τd

time required to return to no-voltage state

τm

mode-locked pulse separation

φ

phase retardation of the half-wave plate

ωsig

frequency (in radians) of the return signal

ωLO

frequency (in radians) of the local oscillator

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