Transcript Folie 1 - RIEGL Laser Measurement Systems

Multi-wavelength airborne laser scanning
ILMF 2011, New Orleans
Dr. Andreas Ullrich
CTO, RIEGL LMS GmbH
introduction: components of ALS systems
full waveform analysis vs. online waveform processing
primary and secondary ALS data products
discussion multi-spectral, hyper-spectral, multi-wavelength
selection criteria for laser wavelength
availability of laser sources
target properties
signal attenuation, background radiation
laser safety
classification of multi-wavelength data / systems
conclusions
contents
RIEGL
VQ-580
RIEGL
VQ-820-G
RiACQUIRE
RIEGL
LMS-Q680i
RiPROCESS
IMU & GPS
RIEGL
DR-680
Flight Guidance
components of ALS systems
Q-560/Q-680i
RIEGL
VQ-580
RIEGL
VQ-820-G
A
dev
A
W
R
R
Full Waveform analysis
range: R [m]
amplitude: A [LSB and
linearized]
echo width: W [ns]
On-Line Waveform Processing
range: R [m]
calibrated amplitude: A [dB]
calibrated reflectance: r [dB]
pulse shape deviation: dev [1]
state-of-the-art echo waveform digitizing systems
RIEGL LMS-Q680i, wavelength 1550 nm
dry conditions
wet snow
primary data: point cloud
RIEGL
VQ-580
wavelength
1064 nm
pulse
amplitude
reflectance
in dB
shape
above
deviation
detection
white
from
threshold
diffusely
expected
reflecting
pulse
target
shape
primary data: point cloud
1064 nm
1550 nm
visible
532 nm
visible
532 nm
1064 nm
1550 nm
images at different wavelengths
Laser Radar Cross Section (LRCS)
cross section  in [m²]
area-normalized cross section values in [m²m-2] or [dB]
by laser footprint area: 
by illuminated object area: 0
  lim 4R 2
R 
E s  Es
Ei
 Ai  d
2
actual geometric crosssection of target
interacting with laser beam


 
0
Alf
reflectance
directivity of
backscattered
reflection

Ai
Radiometric calibration of small-footprint airborne laser scanner measurements: Basic physical
concepts, Wagner, W., ISPRS Journal of Photogrammetry and Remote Sensing, 65, 2010.
radiometric calibration
radiometric calibration
400 nm
800 nm
1200 nm
1600 nm
multispectral
imaging
hyperspectral
imaging
multiwavelength
lidar
hyperspectral
lidar
532 nm
905 nm
1064 nm
1550 nm
supercontinuum laser (500 nm – 2400 nm)
array of receiver channels and ROIC
multispectral/hyperspectral imaging vs. multi-wavelength ALS
pulsed time-of-flight laser ranging: best performance wrt maximum range,
measurement speed, ranging precision and accuracy
selection of wavelength
availability of suitable laser and detector
reflectance of objects
attenuation of atmosphere and background radiation
laser safety
laser requirements
short pulse width (multi-target resolution, high precision)
high peak power (maximum range)
good beam quality (beam divergence, spatial resolution)
high pulse repetition rate (point density)
narrow spectral width (background rejection)
detector requirements
high bandwidth (corresponds to pulse width)
high sensitivity (maximum range)
low noise (high precision)
wavelength selection criteria for ALS sensors
200
400
600
800
1000
UV
1400
1600
1800
2000
INFRARED
diode
905 nm
solid state
fiber
1200
355 nm 532 nm
1064 nm
532 nm
1064 nm
1550 nm
2050 nm
diode lasers, 905 nm
solid state lasers (fundamental wavelength), Nd:YAG, 1064 nm
solid state lasers (harmonics), Nd:YAG, 532 nm, (355 nm)
fiber lasers, Er-doped, 1.55 µm
fiber lasers, Yt-doped, 1.06 µm
fiber lasers, Ho-doped, 2.05 µm
frequency-doubled fiber lasers, 532 nm
suitable laser sources
532 nm
relative reflectance [%]
905 nm
1064 nm
1550 nm
wavelength [µm]
target reflectance versus wavelength
solar spectral irradiance at zenith sun angle 60° at sea level
1400
corresponds to
spectrum of sun light
solar irradiance [W/m²µm]
1200 532 nm
absorption due to
ozone (O3) ,
water vapor (H2O),
oxygen (O2),
carbon dioxide (C02)
1000
800
600
1064 nm
905 nm
400
1550 nm
200
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
wavelength [µm]
background radiation versus wavelength
transmittance [%]
transmittance of 1000 feet horizontal air path (sea level)
1550 nm
905 nm
1064 nm
532 nm
atmospheric transmission
20 km, one way
visibility 23 km, 10 km, 5 km
wavelength [µm]
atmospheric attenuation versus wavelength
absorption coefficient of clear seawater
ultraviolet
visible
attenuation
at depth
10 m
infrared
10 000
attenuation
at depth
0.1 m
attenuation
at depth
1 mm
1 000
100 dB
100
absorption coefficient [cm-1]
50 dB
10 dB
10
1
100 dB
53 dB
0.1
10 dB
0.1 dB
0.01 dB
0.01
100 dB
1 dB
0.001
10 dB
0.1 dB
3.8 dB
0.038 dB
1 dB
0.0001
0.1
0.2
0.4
0.6 0.8 1.0
wavelength [µm]
2.0
4.0
1 dB
0.53 dB
0.01 dB
6.0 8.0 10
attenuation in water versus wavelength
MPE:
maximum
permissible
exposure
parameter:
exposure duration /
pulse width
1550 nm
1064 nm
905 nm
532 nm
355 nm
laser safety considerations
EN60825
class 1
21CFR1040.10
class I
class 1M
-
class 2
class II
class 2M
-
class 3R
class IIIA
class 3B
class IIIB
class 4
class IV
RIEGL
LMSQ680i
RIEGL
RIEGL
VQ-580 VQ-820-G
@ 50kHz
@ 100kHz
@ 80kHz
1.5m
15m
0m
NOHD
NOHD,
NOHD eNOHD
eNOHD
80m
eNOHD
10m
105m
500m
1600m
1600m
1600m
2000m
2000m
2000m
max. range @
reflectance 20%
Range [m]
Laser Safety Standards
max. range @
reflectance 80%
NOHD (nominal ocular hazard distance): distance beyond which
exposure becomes less than maximum permissible exposure (MPE)
extended NOHD: includes the possibility of optically-aided viewing
Laser Classes / NOHD / ENOHD
description
same
area
common
platform
common
scanner
same
IFOV
data set from two different
campaigns
X
data from several laser
scanners on same platform
X
X
several LIDARs sharing the
same scanner
X
X
X
co-axial beams having thus
the same instantaneous
field-of-view
X
X
X
X
additionally pulses of
LIDARs are synchonized
X
X
X
X
synchron
ized
pulses
X
increasing sensor/system complexity
increasing flexibility
classification of multi-wavelength ALS
select scanner model (wavelength) according to target
characteristics, mission requirements, laser safety requirements, ...
 wide variety of applications covered by eye-safe 1550 nm ALS
scanners (e.g., RIEGL LMS-680i and RIEGL VQ-480)
for special applications, e.g., forest health investigations integrate
two or more scanners with different wavelength on a single platform
 providing flexible “multi-wavelength” system (e.g., RIEGL VQ-480
at 1550 nm and RIEGL VQ-580 at 1064 nm)
for hydrography, ad 532 nm LIDAR
regardless of wavelength: echo-digitizing pulsed time-of-flight
systems provide utmost accuracy, multi-target resolution and
calibrated (calibratable) amplitudes and target’s cross-section
conclusions