Calibration of a Terrestrial Laser Scanner - Institute of Geodesy and ...

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8 2. Components of Terrestrial Laser Scannerinterferometry flme-öf-flight triangulationindirectßme-of-flightdirecttime-of-flightFMCW(beat frequency)AMCW(phase difference)polarization modulationFigure 2.1: Opticaldistance measurement methods in terrestrial laser scanners.continuous wave, polarisation modulation. The direct time-of-flight method and the amplitude-modulatedcontinuous wave method are widely-used in terrestrial laser scanners, whereas the frequency-modulatedcontinuous wave method and the polarisation modulation method are rarelyused in terrestrial laser scan¬ners.The intensity of the reflected laser beam defines a fourth dimension, in addition to the 3D coordinates.The reflected laser beam is detected by a photodiode, i.e.PIN diode or avalanche photo diode (APD), andthe amplitude of the detected signal corresponds directly to the intensity of the received laser beam. Theintensity of the laser beam is dependent on several parameters, such as the range, the angleof incidence andthe surface properties, e.g. colour, roughness. Unfortunately, the physical significance of this informationis often not exactly defined by the manufacturers [Lichti et al., 2002a]. Therefore, the intensitycan relateto either the amplitude or the energy of the received signal.For avoiding noise caused by ambient light,additional filters are used, e.g.IR Filter.Since laser scanning is an active and prismless method for surveying the environment, it is necessary tocomment on someaspects of the reflection principles. Often, the results of laser scanning are 3D-models,which have to be illuminated within the software packages. Thus, the section is completed by utilizingsome methods for modeling the reflectance. This is especially the case in computer graphics,models are used for shading the digital models to achieve a realistic appearance with respectwhere severalto illumina¬tion.The term reflectance is defined as the ratio of the amount of electromagnetic radiation, usually light,reflected from a surface to the amount originally strikingthe surface.2.1.1 Electromagnetic WavesElectromagnetic radiation contains a broad spectrum from cosmic radiation with very short wavelengths(A < 10~14m) up to radio waves (A > 106m). Electromagneticwaves are used as carrier waves for trans¬mitting signals, which show varying forms, e.g. impulses, patterns. The specific wavelengththat is useddepends on the layer of the atmosphere, e.g. troposphere, ionosphere, and on the range to be measured. De¬lays during the transmission of the electromagnetic wave between emitter and receiver caused by differentconditions of the atmospherehave to be taken into account. Variationsin temperature, air pressure, hu¬midity, and other parameters influence the speed of light and the propagation of the electromagnetic wave.Thus, the speed of light is not a constant and has to be corrected by applying atmospheric conditions.
"- x"!1984]. terrestrialvary Formaterials.3Laser by emission wavelengthsexample, stimulatedConcerningscanners,from laserof 500 theacronymshown (green) diodefor Figure light800 acontinuous2.3. amplificationnm (near The chip infra-red).basedsemiconductor2.1 Distance and Reflectance Measurement System 9For geodetic applications, the most widely-used electromagnetic waves are the electro-optical waves. Electroopticalradiation (0.4/zmspectrum.< A < 1.3/xm) represents only a small bandwidth of the whole electromagneticThey are appropriate for surveying due to their advantageous properties in the atmosphericlayer close to the earth surface. These waves offer the best compromise in minimizing the absorption in theatmosphere and maximizing both the possibility of bundling and transmission [Hinderung, 2004].Exemplarily, the transmission of the atmosphere for electromagnetic waves with wavelengths from 0.4/zmup to 1.6/xm is shown in Figure 2.2. Transmission is based on the mathematical low resolution transmissionmodel (LOWTRAN). Further information of LOWTRAN can be found in [Richter, 1985].transmission is reached by wavelengths of more than 1.5/xm. The shorter the wavelength,transmission. Furthermore, there are some wavelengths with significantlyThe maximumthe less thelower transmissions. Based onsuch models, the best possible wavelengths for the range and the atmospheric layer in questionfound.can beIjOflANBIE" 01.00TRANSMISSIONE30.900':WTtJt 31.10.38 ÉW mi0.800 : lSä HOftltONTM0..T»L =2 inflïffSPHKff;0,#3 f"v r = 29* kP = w *Q.50O L Hn = SÛG h u (10,«3 ~I0.3»o.a»f"1m= m>._
Page 1: DISS. ETH NO. 17036Calibration of a
Page 5 and 6: ZusammenfassungSeit einigen Jahren
Page 7 and 8: ContentsAbstractiiiZusammenfassungv
Page 9 and 10: Contentsix6.1.3 Results Ill6.2 Stat
Page 11 and 12: 1Introduction1.1 Terrestrial Laser
Page 13: 1.2 Motivation 3Precision [m10~1 "1
Page 16 and 17: 6 1. Introduction
Page 20 and 21: 10 2. Components of Terrestrial Las
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Inormal axis,intersectionpoint axis
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60 3. Calibration of Terrestrial La
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j/-*'.-,•66 3. Calibration of Ter
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74 4. Static Laser Scanning4.1.2 Mi
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76 4. Static Laser ScanningOptical
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78 4. Static Laser Scanningmaximum
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80 4. Static Laser Scanningand gene
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82 4. Static Laser Scanning• Ther
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84 4. Static Laser Scanning4.3.3 NU
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86 4. Static Laser Scanning
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88 5. Kinematic Laser Scanningmirro
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90 5. Kinematic Laser ScanningThe a
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92 5. Kinematic Laser Scanninghas a
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'94 5. Kinematic Laser Scanningbeam
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—96 5. Kinematic Laser ScanningTa
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''iI98 5. Kinematic Laser ScanningA
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40323 o.o; 50545 aT [jjs] 1.0().2 S
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102 5. Kinematic Laser Scanning5.3
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—1.104 5. Kinematic Laser Scannin
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propagationresults series Taylorter
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108 5. Kinematic Laser Scanningonly
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cf.aroundframe regardingsetupusinga
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112 6. Applications of Terrestrial
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acquisitiondescribingFinally, thatM
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132 7. Summaryrange, achievable by
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134 7. Summary
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136 A. Imaging System of Imager 500
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138 B. Technical Data of Imager 500
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u140 C. Adjustment of SphereA =dfi,
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142 C. Adjustment of Sphere
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144 D. Electronic Circuit for Deter
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aMulti-SensorPlatform,PhDGeodesy Sw
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Accuracy-AeinTPS1200 AG, -Version 1
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-GenauigkeitsbetrachtungenInvestiga
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152 BibliographyWunderlich, T. A. [
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List of Figures3.22 Residuals of th
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156 List of Figures
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158 List of Tables
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200220072002Curriculum VitaePersona
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