1. High-Speed High-Density Data Acquisition in Airborne Laser Scanning Applications
INTERGEO
September 2011, Nürnberg
Peter Rieger Andreas Ullrich RIEGL LMS GmbH

2. Range ambiguities in time-of-flight measurements
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
RIEGL Laser Measurement Systems

3. 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 measurements
RIEGL 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 Scanning

4. NEW RIEGL NP680i
Highly compact, flexible and efficient turnkey ALS solution, fully EASA certified, comprising LMS-Q680i, DR560-RD, ALS software, INS/GNSS unit, and FMS, smoothly integrated into the "Universal Nose" of the Diamond twin-engine plane DA42 MPP.
Airborne Laser Scanning

5. Tm Tn Tm+1 Sm En Sm+1 Time Amplitude www.riegl.com
Principle of time-of-flight measurements

6. Definition of „Multiple-Time-Around“
from the “IEEE Standard Radar Definitions, IEEE Std (1998)”:
Definition of „Multiple-Time-Around“

7. MTA Zone 1: Amplitude Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1 Sm-3
En-3
En-2
En-1 En
Sm+1
Time
rm,MTA1
rm-1,MTA1
rm-2,MTA1
rm-3,MTA1
MTA Zone 1

8. MTA Zone 2: Amplitude Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1 Sm-3
En-3
En-2
En-1 En
Sm+1
Time
rm-3,MTA2
rm-2,MTA2
rm-1,MTA2
MTA Zone 2

9. MTA Zone 3: Amplitude Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1 Sm-3
En-3
En-2
En-1 En
Sm+1
Time
rm-4,MTA3
rm-3,MTA3
rm-2,MTA3
MTA Zone 3

10. MTA Zone 4: Amplitude Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Tn Tm+1 Sm-3
En-3
En-2
En-1 En
Sm+1
Time
rm-5,MTA4
rm-4,MTA4
rm-3,MTA4
MTA Zone 4

11. ? Amplitude 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 1
MTA 2 ?
rm,MTA1
MTA 3
rm-1,MTA2
MTA 4
rm-2,MTA3
rm-3,MTA4
MTA Zone 1, 2, 3 or 4 ?

12. Maximum unambiguous range vs. pulse repetition rate
Maximum unambiguous measurement range Ru [m]
400kHz x
Pulse repetition rate [kHz]
Maximum unambiguous range vs. pulse repetition rate

13. 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)
Methods in avoiding or resolving range ambiguities

14. Avoiding range ambiguities in flight planning
MTA zone 1
MTA zone 2
MTA zone 3
Avoiding range ambiguities in flight planning

15. Avoiding range ambiguities in flight planning
Avoiding range ambiguities in flight planning

16. www.riegl.com Spatial Multiplexing
Spatial separation by scanner orientation
Spatial separation by mirror synchronization
1 PPS
typ. > 1 deg
typ. > 10 deg
deam divergence typ. < 0.5 mrad
Spatial Multiplexing

17. Wavelength multiplexing
Wavelength multiplex by using 2+ wavelengths
532 nm
1064nm
1550 nm
VQ-820G
VQ-580
Q-680i
Wavelength multiplexing

18. Resolving range ambiguities by spatial analysis
Resolving range ambiguities by spatial analysis

19. Advantages and Disadvantages
Method
Advantages
Disadvantages
Flight Planning
Complex and dangerous in difficult terrain
Spatial multiplexing
Overall 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 analysis
Algorithms adaptable to application
Tuning of algorithms if neccessary
apriori knowledge of terrain required
Advantages and Disadvantages

20. New approach, Step 1: Variation of pulse repetition intervals
Amplitude
Time 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
rm,MTA2 = rtrue
rm+1,MTA2 = rtrue
rm+2,MTA2=rtrue
rm,MTA1
rm+1,MTA1
rm+2,MTA1
rm+3,MTA1
τ = PRR-1
Δtm+1 τ
Δtm+2
Δtm+3
Δtm+4
τ = PRR-1
Δtm+1 τ
Δtm+2
Δtm+3
Δtm+4
New approach, Step 1: Variation of pulse repetition intervals

21. New approach, Step 2: Analysis of the influence of PRI jitter
New approach, Step 2: Analysis of the influence of PRI jitter

22. RIEGL LMS-Q680i RIEGL VQ-580 RiMTA
full waveform airborne laser scanner
RIEGL VQ-580
online waveform processing
airborne laser scanner
RiMTA
automated range ambiguity resolution
RiMTA

23. One scan stripe transits 3 MTA Zones
RIEGL LMS-Q680i
PRR = 400kHz
Ru = 375m
Alt AGL [m]
t [s]
140
120
100 80 60 40 20
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
One scan stripe transits 3 MTA Zones

24. MTA 3 MTA 2 MTA 1 RIEGL LMS-Q680i PRR = 400kHz Ru = 375m www.riegl.com
Alt AGL [m]
t [s]
140
120
100 80 60 40 20
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
One scan stripe transits 3 MTA Zones

25. MTA 3 MTA 2 MTA 1 RIEGL LMS-Q680i PRR = 400kHz Ru = 375m www.riegl.com
Alt AGL [m]
t [s]
140
120
100 80 60 40 20
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
One scan stripe transits 3 MTA Zones

26. MTA 3 MTA 2 MTA 1 RIEGL LMS-Q680i PRR = 400kHz Ru = 375m www.riegl.com
Alt AGL [m]
t [s]
140
120
100 80 60 40 20
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
One scan stripe transits 3 MTA Zones

27. MTA 3 MTA 2 MTA 1 RIEGL LMS-Q680i PRR = 400kHz Ru = 375m www.riegl.com
Alt AGL [m]
t [s]
140
120
100 80 60 40 20
200
300
1000
900
800
400
500
600
700
MTA 3
MTA 2
MTA 1
One scan stripe transits 3 MTA Zones