Centre dedocumentation
scientifique

Development of a dispersometer for the implementation into geodetic high-accuracy direction measurement systems / Burkhard Böckem (2001)  

Public Titre : Development of a dispersometer for the implementation into geodetic high-accuracy direction measurement systems Type de document : Thèse/HDR Auteurs : Burkhard Böckem, Auteur Editeur : Zurich : Institut für Geodäsie und Photogrammetrie IGP - ETH Année de publication : 2001 Collection : IGP Mitteilungen, ISSN 0252-9335 num. 73 Importance : 140 p. Format : 21 x 30 cm ISBN/ISSN/EAN : 978-3-906467-33-7 Note générale : Bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Géodésie [Termes IGN] effet atmosphérique [Termes IGN] émetteur [Termes IGN] impulsion laser [Termes IGN] mesurage électronique d'angles [Termes IGN] mesurage électronique de distances [Termes IGN] propagation du signal [Termes IGN] rayonnement électromagnétique [Termes IGN] récepteur bifréquence [Termes IGN] réfraction atmosphérique [Termes IGN] téléscope Résumé : (Auteur) In the course of the progressive developments of sophisticated geodetic systems which offer a very high accuracy potential strategies for correcting atmosphere-related effects will become increasingly important. These atmosphere-related effects arise in a large span of time scales: systematic deviations caused by a quasi-stationary refractive index gradient environment, generally referred to as refraction in geodetic context, slowly transfer to stochastic deviations resulting from optical turbulence. Refraction corrected optical direction and angle measurements are required in numerous high-accuracy measurement applications. These applications include surveying tasks in connection with civil engineering projects, the alignment of particle accelerator facilities, surveying tasks in context within assembling processes in industrial environments, e.g. aircraft industry, tasks wherein surveying instruments provide the spatial guidance of large machines, etc. A dispersometer, based on the dual-wavelength method by utilizing atmospheric dispersion, constitutes a metrological solution to atmosphere-related effects. Another decisive advantage of a dispersometer is that the envisaged correction of atmosphere-related effects works integrally and is available in real time. The aim of this thesis was to develop this dispersometer to overcome atmospherically induced limitations in very high-accuracy direction and angle measurements. The dispersometer consists of two modules: the dual-wavelength transmitter and the detection system being composed of the dispersion telescope and a position sensitive detector. By applying the dual-wavelength method, the major .challenges in instrumental realization are the generation of coaxial single-mode emission at two spectrally optimized wavelengths and the achievement of optical position sensing accuracy in the order of a few nanometers. The development of the dispersometer is principally made possible by focussing on three key technologies: dual-wavelength generation by frequency conversion, optical fiber technology, and gap- technology. Within this work detailed studies of these three key technologies are performed. In this work it is demonstrated that a dual-wavelength laser by frequency conversion is clearly suited for the implementation in the dual-wavelength transmitter. Furthermore, a novel technique for achieving coaxial single-mode propagation at two spectrally wide-separated wavelengths by one single-mode fiber is established within this thesis. Due to the application of optical fiber technology it is now possible to couple both beams into one optical channel of a modem geodetic total station. In order to achieve optical position sensing with the accuracy of a few nanometers by using a short-focal-length receiving telescope, gap-technology by utilizing special segmented position sensitive detectors is applied. This thesis contains a complete treatment addressed to this technology. Within the course of dispersometer performance tests, difference position sensing accuracy of ó = 7.3 nm was achieved. Additionally, the existence of the position sensitive detector inherent dispersion was demonstrated. In combination with the dispersion of the receiving optics, the position sensitive detector inherent dispersion has to be considered for the measurement of the atmospheric dispersion induced displacement between both beams of different wavelengths. As a solution a self-calibration procedure which corrects the dispersion of the complete detection system is described. This self-calibration procedure which utilizes the impact of optical turbulence possesses the decisive advantages that it obviates the need of additional measurements and the dispersion correction can be computed and applied in real time. A substantial part of this thesis is devoted to dispersometer measurements. Two basic atmospheric conditions which are typical for industrial measurement tasks indoors were simulated. Additionally, a detailed study of the influence of the aperture diameter on the dispersometer measurements was performed. The optimal aperture diameter for the present instrumental layout and for the prevailing ambient conditions was 30 mm. For theodolite-like and smaller apertures it is confirmed that the accuracy of the refraction angle improves with the square root of the integration time. Due to dispersometer performance by using theodolite-like and possibly smaller apertures in combination with the self-calibration procedure, the implementation of a standard theodolite-telescope is proposed. In a moderately turbulent atmosphere the accuracy of the refraction angle for single- face telescope observation was found to be 0.2 µrad (0.01 mgon) after an integration time of 12 sand a sight length of 17 m. Summarizing the theoretical investigations, the key technologies involved in the instrumental development, and the experimental results, presented in this dissertation, it can be concluded that the realized dispersometer in combination with a theodolite is capable of the refraction corrected angular measurements, the influences of optical turbulence notwithstanding. The application of optical fiber technology and the envisaged implementation of a standard theodolite-telescope confirm the presumption that the realized dispersometer can be implemented into modem geodetic total stations. Improvements with respect to field-operativeness are expected by an industrial realization of the dispersometer and by implementing the dispersometer into modem geodetic total stations. The integration of blue laser diodes, when meeting the standards of nowadays infrared laser diodes, would significantly enhance efficiency and reduce overall costs. Due to the technologies presented within this thesis such an integration is clearly feasible. Numéro de notice : 14740 Affiliation des auteurs : non IGN Autre URL associée : http://dx.doi.org/10.3929/ethz-a-004176211 Thématique : POSITIONNEMENT Nature : Thèse étrangère DOI : 10.3929/ethz-a-004176211 En ligne : http://e-collection.library.ethz.ch/eserv/eth:24109/eth-24109-02.pdf Format de la ressource électronique : URL Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=62684

Réservation

Réserver ce document

Exemplaires (1)

Code-barres	Cote	Support	Localisation	Section	Disponibilité
14740-01	30.03	Livre	Centre de documentation	En réserve 2S (M-103)	Disponible