3. 2D/3D Wind profiling:
LIDAR (Light Detection And Ranging)
is an optical remote sensing technology that measures properties of backscattered light
to find range or other information of a distant target .
To work the Lidar needs some form of backscattering (Rayleigh, Mie, Raman, aerosols etc, )
L idar Concept Beam forming and
steering optics
L aser control Solid,
K eopsys liquid, gas
Data processing
Pulsed
Time-of-flight
L aser
F requency shift
Depolarization Scattered light
Detector collection optics
Differential abs.
Remote M easurements:
Remote Measurements: Time-of-F light (T O F) > Distance
Time of Flightshift > Velocity=
F requency (TOF) Distance
Frequncy shift > M acro composition
Depolarization = Velocity
Depolarization
Differential A bsorption > =hemical comp.
C Macro composition
6
Differential Absorption =
Jean-Marc Delavaux, Feb 23-2010
Chemical component
4. 2D/3D Wind profiling:
LIDAR - Laser Operating Mode
Pulsed Lasers
Most commonly used for ranging applications ¬ Remote Measurement systems include a laser
transmitter, an optical telescope receiver that amplifies the backscatter, and high sensitivity photo-
detector to convert optical energy into electrical impulses.
Distance to object is determined by the time taken by the transmitted pulse to the target and back.
Time of Flight (TOF) LIDAR
! Non coherent source to avoid optical speckle
5. 2D/3D Wind profiling:
LIDAR - Laser Operating Mode
Continous Wave (CW) Lasers
Transmit a continuous signal, and ranging is carried out by modulating the phase of the laser light.
Rely also on the Doppler effect.
Travel time is directly proportional to the phase difference between the received and transmitted
sinusoidal signal.
Coherent LIDAR
(Velocity Measurements)
! Laser linewidth < 10 MHz
! Increased signal to noise ratio SNR for ranging by using spectral filtering
6. 2D/3D Wind profiling:
L aser -Requirements for L idar
LIDAR Laser Requirements (1)
A ttributes Ranging L idar Coherent L idar
O perating The must be highly reflective on the target and transparent
through the medium
Eye safe wavelength >1.4µm, 1.5µm is preferred, but other
wavelengths ( i.e. Visible, IR) are chosen to match application
requirements
O utput power The range of distances is related to power level. The higher the
better, provided other attributes of the source are conserved
C enter Not necessary but helps SNR at Very important to facilitate
A ccuracy & receiver by additional filter. coherent detection, in particular
Stability DIAL measurements
Coherence Not important, Low Coherent length must be equal
L ength coherent prevents speckle. or greater than measurement
range
L ine-width ( ) Not important, may help Linewidth must be smalller than
efficiency & SNR minimum range value
10
Jean-Marc Delavaux, Feb 23-2010
7. 2D/3D Wind profiling:
L aser - Requirements for L idar (2)
LIDAR Laser Requirements (2)
A ttributes Ranging L idar Coherent L idar
Relative intensity Not important, although may Very important ! One of the
noise, R I N become important in multiple limiting factor for the system
pulse measurement Lidar sensitivity the higher the RIN
the less sensitive be the lidar
RIN<-140dBc/Hz at fc<10kHz
Sensitivity to Not important Very important, can have
vibration detrimental effect on stability
if system is used in harsh
environment
O perating Generally important. Very important, can have
temperature In particular airborne detrimental effect on stability
/spatial, & military if system is used in harsh
applications environment
Reliability Important Very important
Cost Low to moderate High to very high
11
Jean-Marc Delavaux, Feb 23-2010
8. 2D/3D Wind profiling:
LIDAR – Laser System Characteristics
Pulse Energy (E) total energy content of a pulse (typically 100 µJ to several mJ).
Pulse Duration (t) is usually defined as the time during which the laser output pulse power remains
continuously above half its maximum value or peak power (FWHM), (i.e. 1ns to 1µs, typically 10 ns).
Pulse Repetition Frequency (PRF or f) (kHz) – number of emitted pulses per second
(ranges from 1 to 200 kHz)
Beam Divergence (!) is usually defined by the output fiber beam divergence (i.e. M2 or BPP)
limited by diffraction, typically 0.3 to 2mrad.
Scan Rate –number of times per second a scanning device samples its field of view (25 –1000 Hz)
Wind Power Plant Doppler Beam Swinging Profiler (principle) The flow field behind two wind turbines (symbolised by a vertical black lines)
9. 2D/3D Wind profiling:
LLASER versus LIDAR parameters
aser versus L idar Parameters
L aser L idar
Relation
Parameter Parameter
Pulse Rate (PR F) Range (z) PR F(k H z)<c/2z(m)
z=1000m => PR F <150k H z
Pulse width ( ) Range Resolution( z) (ns)=6x z(m)
Sample depth 10ns =>1.5m at speed of light
Beam Divergence ( Trans. Resolution (Sx) Sx= z (mrad)
Beam quality: BPP (Spot diameter ) = 1 mrad @ z = 1km. Sx=1m
( mm x mrad)
E nergy-per-Pulse (E) SN R E SN R 2
L inewidth ( ) Velocity (V) (MHz)< 2V(m/s) / (um)
Coherent only
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10. 2D/3D Wind profiling:
Laser Operating Wavelength
In theory, any light source can be used to create a LIDAR instrument
Traditionally solid-state Nd:YAG lasers at 1064nm (NIR) & 532nm (green)
wavelengths have been used in LIDARS
Newer LIDAR designs and applications rely on reliable optical fiber laser
technology.
High performance LIDAR sources are commercially available,
from Keopsys, at Visible ( 532nm), Near-Infrared (NIR-1064/1550nm) & Middle
infrared (MIR-2000nm) wavelengths.
Fiber lasers are attractive because they offer:
! Combined high collimation and high optical power
! „Eye safe”, compact & low power consumption solutions
! Versatile properties adaptable to specific applications
11. EOLA! Series
Eye-safe long pulse amplifiers
Features:
! High energy per pulse up to 100 !J
! Peak power up to 250 W
! Long pulses from 200 to 400 ns
! Repetition frequency from 10 to 20 kHz
! Fourier transformed limited operation
! Polarization Maintaining
! Diffraction limited or M2<1.5 for pulse
energy >15 !J Keopsys can also provide the laser
version of this product upon request
Ideal for wind profiling by Doppler heterodyne LiDAR systems
12. SPIDERLITE MSA! Series
Ultra compact multiple ports high power fiber amplifiers
Features:
! Multi-ports configurations from 1x30 dBm to 8x20 dBm
! Low noise figure
! Low power consumption
! Low analog signal distorsion
Ideal for:
! Sensing
! Highly integrated fiber optic systems
New! Available in PM
13. SPARK!frequency fiber laser
Eye-safe CW single
Series
Features:
! Output power up to 2 W
! Operating wavelength from 1545 to 1565 nm
! Narrow linewidth, single frequency
! Ultra low RIN
! Low phase noise
! Random or linear polarization
! Diffraction limited output
! OEM module with RS232
Ideal for wind speed measurements from windmill cradle
14. KULT! Series
1 !m ultra compact laser transmitter
Features:
! Pulse energy up to 10 !J
! Peak power up to 10 kW
! Pulsewidth of 0.1 ns and from 1 to 30 ns
! Repetition frequency from 10 Hz to 1 MHz
! Diffraction limited output
! Can be doubled to 532 nm
All KULT! versions are ideal for:
! Cloud height measurement
! Range finding
! Telemetry
! 3D scanning
15. KULT! Series
Eye safe ultra compact laser transmitter
1.5 !m Features:
! Pulse energy up to 50 !J
! Peak power up to 10 kW
! Pulsewidth from 0.5 to 200 ns
! Repetition frequency from 10 Hz to 1 MHz
! Diffraction limited output 1.5 "m
! PM version available
2 !m Features:
! Pulse energy up to 15 !J
! Peak power up to 1.5 kW
! Pulsewidth from 10 to 40 ns
! Repetition frequency from 5 Hz to 20 kHz
! Diffraction limited output
2 "m
16. MIRVISION! Series
Eye-safe high power laser transmitter
Features:
! High pulse energy combined with good beam
quality (80 !J and M2<1.5 or >100 !J and M2<3)
! High peak power up to 25 kW
! Pulsewidth from 1 to 10 ns
! Repetition frequency from 20 kHz to 1 MHz
Ideal for:
! Range finding
! Obstacle detection
! Airborne applications
17. LIDAR DEFENCE TELEMETRY INDUSTRY R&D TELECOM T&M MEDICAL FTTx
The ys to
Your tical
tems
Steven D. Wagner
Sales & Marketing Manager KEOPSYS SA.
swagner@keopsys.com 21 rue Louis de Broglie
Direct: + 49 89 309 040 271 22300 Lannion, France
Tel: +33 2 96 05 08 40
Cell: +49 152 56 77 77 76 Fax: +33 2 96 05 08 01
16.03.11 31
