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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 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. www.riegl.com for planes: for helicopters: 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 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 Amplitude Sm En Tm www.riegl.com Sm+1 Tn Tm+1 Time Principle of time-of-flight measurements from the “IEEE Standard Radar Definitions, IEEE Std 686-1997 (1998)”: www.riegl.com Definition of „Multiple-Time-Around“ Amplitude MTA Zone 1: Sm-3 Tm-3 Sm-2 Sm-1 En-1 En-3 En-2 Tn-3 Tm-2 Tn-2 Tm-1 rm-3,MTA1 rm-2,MTA1 rm, MTA1 www.riegl.com Sm En Tn-1 Tm rm-1,MTA1 Sm+1 Tn Tm+1 Time rm,MTA1 c (Tn Tm ) 2 MTA Zone 1 Amplitude MTA Zone 2: Sm-3 Tm-3 Sm-2 Sm-1 En-3 En-2 Tn-3 Tm-2 Tn-2 Tm-1 Sm En-1 Tn-1 Tm Sm+1 En Tn Tm+1 Time rm-3,MTA2 rm-2,MTA2 rm-1,MTA2 rm1, MTA 2 www.riegl.com c (Tn Tm1 ) 2 MTA Zone 2 Amplitude MTA Zone 3: Sm-3 Tm-3 Sm-2 Sm-1 Sm En-1 En-3 En-2 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Sm+1 En Tn Tm+1 Time rm-4,MTA3 rm-3,MTA3 rm-2,MTA3 rm2, MTA3 www.riegl.com c (Tn Tm2 ) 2 MTA Zone 3 Amplitude MTA Zone 4: Sm-3 Tm-3 Sm-2 Sm-1 Sm En-1 En-3 En-2 Tn-3 Tm-2 Tn-2 Tm-1 Tn-1 Tm Sm+1 En Tn Tm+1 Time rm-5,MTA4 rm-4,MTA4 rm-3,MTA4 rm3, MTA 4 www.riegl.com c (Tn Tm3 ) 2 MTA Zone 4 Amplitude Sm-3 Sm-2 Sm-1 Sm Sm+1 MTA 1 En-3 En-1 En-2 En MTA 2 Tm-3 Tn-3 Tm-2 Tn-2 Tm-1 ? Tn-1 Tm Tn Tm+1 Time rm,MTA1 MTA 3 rm-1,MTA2 rm-2,MTA3 MTA 4 rm-3,MTA4 www.riegl.com MTA Zone 1, 2, 3 or 4 ? Maximum unambiguous measurement range Ru [m] 1000 900 c PRR1 Ru 2 800 700 600 500 Ru=375m @ 400kHz 400 x 300 200 100 100 200 300 400 500 600 700 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 MTA zone 1 MTA zone 2 MTA zone 3 www.riegl.com Avoiding range ambiguities in flight planning www.riegl.com Avoiding range ambiguities in flight planning Spatial separation by scanner orientation Spatial separation by mirror synchronization 1 PPS typ. > 1 deg deam divergence typ. < 0.5 mrad www.riegl.com Spatial Multiplexing Wavelength multiplex by using 2+ wavelengths 200nm 400 600 800 1000 1200 UV 305nm 1400 1600 1800 2000 INFRARED 532nm 905nm 1.06μm diode laser frequency doubled fiber laser 1.55μm solid state laser, Nd:YAG, fundamental wavelength 2.05μm fiber laser, Er-doped fiber laser, Ho-doped fiber laser, Yt-doped solid state laser, Nd:YAG, harmonics www.riegl.com 532 nm 1064nm 1550 nm VQ-820G VQ-580 Q-680i Wavelength multiplexing u R ,M TA 1 r2 ,M TA 1 2 Ru MT A2 r1, r2 Ru 3 ,M TA 1 r2 www.riegl.com Resolving range ambiguities by spatial analysis Method Advantages Disadvantages Complex and dangerous in difficult terrain Flight Planning Spatial multiplexing Overall pulse repetition rate doubled Doubling sales for manufacturer Wavelength multiplexing Additional attributes for target classification, e.g., vegetation indices +1 scanner → only +1Ru Higher investment for customer Irregular point pattern Complex system Spatial data analysis Algorithms adaptable to application Tuning of algorithms if neccessary apriori knowledge of terrain required www.riegl.com Advantages and Disadvantages Amplitude Sm Sm+1 Tm Sm+2 En En+1 Tn Tm+1 Tn+1 rm,MTA1 Tm+2 Tn+2 τ rm+1,MTA1 Sm+4 En+2 Δtm+2 Δtm+1 τ = PRR-1 Sm+3 τ rm+2,MTA1 En+3 Tn+3 Tm+4Time Tm+3 Δtm+3 Δtm+4 τ rm+3,MTA1 rm,MTA2 = rtrue rm+1,MTA2 = rtrue rm+2,MTA2=rtrue www.riegl.com New approach, Step 1: Variation of pulse repetition intervals 170 MTA-zone 1 175 180 185 860 880 900 920 i 940 E X MTAj MTA-zone 3 930 935 940 945 N 1 EX MTA3 1965.5m 860 880 900 i www.riegl.com 2 920 940 MTA-zone 22 E X MTA 2 156 .9m 550 555 560 565 X i 1 925 target range [m] target range [m] E X MTA1 1847m 545 2 target range [m] target range [m] 165 860 2 ~ MTAj 880 900 920 940 i i 1305 MTA-zone 4 1310 1315 1320 1325 E X MTA 4 1825.2m2 860 880 900 920 940 i New approach, Step 2: Analysis of the influence of PRI jitter RIEGL LMS-Q680i RIEGL VQ-580 RiMTA full waveform airborne laser scanner online waveform processing airborne laser scanner automated range ambiguity resolution www.riegl.com RiMTA RIEGL LMS-Q680i PRR = 400kHz Ru = 375m 1000 MTA 3 Alt AGL [m] 900 800 700 MTA 2 600 500 400 MTA 1 300 200 0 www.riegl.com 20 40 60 80 t [s] 100 120 140 One scan stripe transits 3 MTA Zones RIEGL LMS-Q680i PRR = 400kHz Ru = 375m 1000 MTA 3 Alt AGL [m] 900 800 700 MTA 2 600 500 400 MTA 1 300 200 0 www.riegl.com 20 40 60 80 t [s] 100 120 140 One scan stripe transits 3 MTA Zones RIEGL LMS-Q680i PRR = 400kHz Ru = 375m 1000 MTA 3 Alt AGL [m] 900 800 700 MTA 2 600 500 400 MTA 1 300 200 0 www.riegl.com 20 40 60 80 t [s] 100 120 140 One scan stripe transits 3 MTA Zones RIEGL LMS-Q680i PRR = 400kHz Ru = 375m 1000 MTA 3 Alt AGL [m] 900 800 700 MTA 2 600 500 400 MTA 1 300 200 0 www.riegl.com 20 40 60 80 t [s] 100 120 140 One scan stripe transits 3 MTA Zones RIEGL LMS-Q680i PRR = 400kHz Ru = 375m 1000 MTA 3 Alt AGL [m] 900 800 700 MTA 2 600 500 400 MTA 1 300 200 0 www.riegl.com 20 40 60 80 t [s] 100 120 140 One scan stripe transits 3 MTA Zones