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

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 www.riegl.com RIEGL Laser Measurement Systems

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 www.riegl.com Airborne Laser Scanning

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. www.riegl.com Airborne Laser Scanning

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

Definition of „Multiple-Time-Around“ from the “IEEE Standard Radar Definitions, IEEE Std 686-1997 (1998)”: www.riegl.com Definition of „Multiple-Time-Around“

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 www.riegl.com MTA Zone 1

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 www.riegl.com MTA Zone 2

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 www.riegl.com MTA Zone 3

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 www.riegl.com MTA Zone 4

? 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 www.riegl.com MTA Zone 1, 2, 3 or 4 ?

Maximum unambiguous range vs. pulse repetition rate Maximum unambiguous measurement range Ru [m] Ru=375m @ 400kHz x Pulse repetition rate [kHz] www.riegl.com Maximum unambiguous range vs. pulse repetition rate

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 www.riegl.com Avoiding range ambiguities in flight planning

Avoiding range ambiguities in flight planning www.riegl.com Avoiding range ambiguities in flight planning

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 www.riegl.com Spatial Multiplexing

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

Resolving range ambiguities by spatial analysis www.riegl.com Resolving range ambiguities by spatial analysis

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 www.riegl.com Advantages and Disadvantages

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 www.riegl.com New approach, Step 1: Variation of pulse repetition intervals

New approach, Step 2: Analysis of the influence of PRI jitter  www.riegl.com New approach, Step 2: Analysis of the influence of PRI jitter

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 www.riegl.com RiMTA

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 www.riegl.com One scan stripe transits 3 MTA Zones

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 www.riegl.com One scan stripe transits 3 MTA Zones

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 www.riegl.com One scan stripe transits 3 MTA Zones

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 www.riegl.com One scan stripe transits 3 MTA Zones

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 www.riegl.com One scan stripe transits 3 MTA Zones