www.riegl.com high-speed high-density data acquisition in airborne laser scanning applications...
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www.riegl.com
High-Speed High-Density Data Acquisition in Airborne Laser Scanning Applications
INTERGEOSeptember 2011, Nürnberg
Peter Rieger Andreas Ullrich
RIEGL LMS GmbH
www.riegl.com RIEGL Laser Measurement Systems
Contents:
● Range ambiguities in time-of-flight measurements● Known measures in resolving or avoiding range ambiguities● Advantages and disadvantages● Introduction to RIEGL’s novel approach
Airborne laser scanning is a rapid, highly accurate and efficient method of capturing 3D data of large areas.
for planes:
LMS-Q680i / LMS-Q560• Multiple-Time-Around (MTA) Processing (LMS-Q680i)• Full Waveform Analysis for an unlimited number of target echoes • operating flight altitude up to 5,000 / 3,300 ft AGL • Laser PRR 400 / 240 kHz
for helicopters:
NEW RIEGL VQ-580• optimized for glacier and snow measurementsRIEGL VQ-480 / VQ-380• echo digitization and Online Waveform Processing• multiple target capability• operating flight altitude up to 2,500 / 1,800 ft AGL
Airborne Laser Scanningwww.riegl.com
Principle of time-of-flight measurementswww.riegl.com
Am
plit
ude
Tm Tn Tm+1
Sm
En
Sm+1
Time
Definition of „Multiple-Time-Around“
from the “IEEE Standard Radar Definitions, IEEE Std 686-1997 (1998)”:
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MTA Zone 1
Am
pli
tud
e
Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1
Sm-3 Sm-2 Sm-1 Sm
En-3 En-2
En-1 En
Sm+1
Timerm,MTA1rm-1,MTA1
rm-2,MTA1rm-3,MTA1
MTA Zone 1:
2
)(1,
mnMTAm
TTcr
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MTA Zone 2
Am
pli
tud
e
Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1
Sm-3 Sm-2 Sm-1 Sm
En-3 En-2
En-1 En
Sm+1
Time
rm-1,MTA2
rm-2,MTA2
rm-3,MTA2
MTA Zone 2:
2
)( 12,1
mn
MTAm
TTcr
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MTA Zone 3
Am
pli
tud
e
Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1
Sm-3 Sm-2 Sm-1 Sm
En-3 En-2
En-1 En
Sm+1
Time
MTA Zone 3:
rm-2,MTA3
rm-3,MTA3
rm-4,MTA3
2
)( 23,2
mn
MTAm
TTcr
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MTA Zone 4
Am
pli
tud
e
Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1
Sm-3 Sm-2 Sm-1 Sm
En-3 En-2
En-1 En
Sm+1
Time
MTA Zone 4:
rm-3,MTA4
rm-4,MTA4
rm-5,MTA4
2
)( 34,3
mn
MTAm
TTcr
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MTA Zone 1, 2, 3 or 4 ?
Am
pli
tud
e
Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1
Sm-3 Sm-2 Sm-1 Sm
En-3 En-2
En-1 En
Sm+1
Time
rm,MTA1
rm-1,MTA2
rm-2,MTA3
rm-3,MTA4
?
MTA 1
MTA 2
MTA 4
MTA 3
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Maximum unambiguous range vs. pulse repetition rate
100
200
300
400
500
600
700
800
900
1000
100 200 300 400 500 600 700
2
1
PRRcRu
Ru=375m @ 400kHz
x
Ma
xim
um
un
am
big
uo
us
me
as
ure
me
nt
ran
ge
Ru [
m]
Pulse repetition rate [kHz]
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Known methods in avoiding range ambiguities:
● careful choice of operating altitudes● Spatial multiplexing: 2 x RIEGL LMS-Q680i ● Wavelength multiplexing: RIEGL VQ-820-G (532nm), RIEGL VQ-580 (1064nm)
Known methods in resolving range ambiguities:
● Spatial analysis based on known distance (RiANALYZE)
www.riegl.com Methods in avoiding or resolving range ambiguities
Avoiding range ambiguities in flight planning
MTA zone 1
MTA zone 2
MTA zone 3
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Avoiding range ambiguities in flight planningwww.riegl.com
Spatial Multiplexing
typ. > 1 deg
deam divergence typ. < 0.5 mrad
Spatial separation by scanner orientation Spatial separation by mirror synchronization
1 PPS
typ. > 10 deg
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Wavelength multiplexing
200nm 400 600 800 1000 1200 1400 1600 1800 2000
diode laser solid state laser, Nd:YAG,fundamental wavelength
fiber laser, Yt-doped frequency doubled fiber laser
solid state laser, Nd:YAG, harmonics
fiber laser, Ho-doped
fiber laser, Er-doped
INFRARED
305nm 532nm 905nm 1.06μm 1.55μm 2.05μm
UV
Wavelength multiplex by using 2+ wavelengths
1550 nm1064nm532 nm
VQ-820G VQ-580 Q-680i
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Resolving range ambiguities by spatial analysis
2,1M
TA
r u
MTA
R
r
21
,2
u
MTA
R
r
31
,2
u
MTA
R
r
1,2
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Advantages and Disadvantages
Method Advantages Disadvantages
Flight PlanningComplex and dangerous in difficult terrain
Spatial multiplexingOverall pulse repetition rate doubled
Doubling sales for manufacturer
+1 scanner → only +1Ru
Higher investment for customer
Irregular point pattern
Complex system
Wavelength multiplexing
Additional attributes for target classification, e.g., vegetation indices
Spatial data analysisAlgorithms adaptable to application
Tuning of algorithms if neccessaryapriori knowledge of terrain required
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τ = PRR-1
Δtm+1
τ
Δtm+2
τ
Δtm+3
τ
Δtm+4
τ = PRR-1
Δtm+1
τ
Δtm+2
τ
Δtm+3
τ
Δtm+4
Sm Sm+1 Sm+2 Sm+3
En En+1
En+2
Tm Tn Tm+1 Tn+1 Tm+2 Tn+2
En+3
Tm+3 Tn+3
Sm+4
Tm+4
New approach, Step 1: Variation of pulse repetition intervals
Am
plit
ude
Time
rm,MTA2 = rtrue
rm+1,MTA2 = rtrue
rm+2,MTA2=rtrue
rm,MTA1 rm+1,MTA1rm+2,MTA1 rm+3,MTA1
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165
860 880 900 920 940
170
175
180
185
545
860 880 900 920 940
550
555
560
565
1305
860 880 900 920 940
1310
1315
1320
1325
925
860 880 900 920 940
930
935
940
945
ii
targ
et r
ange
[m
]ta
rget
ran
ge [
m]
ii
targ
et r
ange
[m
]ta
rget
ran
ge [
m]
ii
targ
et r
ange
[m
]ta
rget
ran
ge [
m]
ii
targ
et r
ange
[m
]ta
rget
ran
ge [
m]
MTA-zone 2MTA-zone 1
MTA-zone 4MTA-zone 3
New approach, Step 2: Analysis of the influence of PRI jitter
1
1
2~
N
i
MTAjMTAjXi
XE
21 1847mE MTAX 2
2 9.156 mE MTAX
23 5.1965 mE MTAX 2
4 2.1825 mE MTAX
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RiMTA
RIEGL LMS-Q680ifull waveform
airborne laser scanner
RIEGL VQ-580online waveform processing
airborne laser scanner
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RiMTAautomated range
ambiguity resolution
One scan stripe transits 3 MTA Zones
RIEGL LMS-Q680i
PRR = 400kHz
Ru = 375m
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Alt
AG
L [
m]
t [s]0 14012010080604020
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
RIEGL LMS-Q680i
PRR = 400kHz
Ru = 375m
www.riegl.com One scan stripe transits 3 MTA Zones
Alt
AG
L [
m]
t [s]0 14012010080604020
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
RIEGL LMS-Q680i
PRR = 400kHz
Ru = 375m
www.riegl.com One scan stripe transits 3 MTA Zones
Alt
AG
L [
m]
t [s]0 14012010080604020
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
RIEGL LMS-Q680i
PRR = 400kHz
Ru = 375m
www.riegl.com One scan stripe transits 3 MTA Zones
Alt
AG
L [
m]
t [s]0 14012010080604020
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
RIEGL LMS-Q680i
PRR = 400kHz
Ru = 375m
www.riegl.com One scan stripe transits 3 MTA Zones
Alt
AG
L [
m]
t [s]0 14012010080604020
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1