Entwicklung und Erprobung eines digitalen Zenitkamerasystems für die hochpräzise Lotabweichungsbestimmung

This Ph.D. thesis presents the Digital Zenith Camera System TZK2-D as a high-precision astrogeodetic instrumentation for the determination of the direction of the plumb line and its vertical deflection. Emphasis is placed on instrumental construction, automated data acquisition and processing in real-time and appropriate calibration procedures. The measuring system has been extensively
tested and used for economic determination of vertical deflections in several field campaigns. The Digital Zenith Camera System TZK2-D consists of two major components: A zenith camera equipped with a CCD is used for the determination of the plumb line and a GPS-receiver for precise timing and measurement of ellipsoidal coordinates. The combination of both components allows the determination of vertical deflections online in a nearly completely automated procedure. As integral part of the TZK2-D system the CCD provides digital image data immediately after acquisition, which is why the complete processing procedure is accelerated considerably compared to those of
formerly used analogue zenith cameras. Fully automated data processing is performed using the software system AURIGA. For the main processing steps, the extraction of imaged stars is performed applying the point spread function.
Reference stars are provided by high density, highly accurate star catalogues Tycho-2 and UCAC as realizations of the ICRS. Astrometric data reduction leads to the direction of the plumb line and its deflection from the ellipsoidal normal taking GPS-measurements into account. Due to the extensive calibration of the measurement system and appropriate modelling of instrumental errors, an internal accuracy of better than 0′′. 1 is achieved for vertical deflection measure-
ments. Estimates of the system’s external accuracy are obtained by repeated measurements over different nights and comparisons at several reference stations. The external accuracy has been found to be about 0′′. 10 to 0′′. 15 as such exceeding considerably the accuracy of conventional zenith cameras. The determination of the vertical deflection lasts approximately 30 min including set up time, acquisition of 60 single measurements and processing time. Consequently, the Digital Zenith Camera System TZK2-D is a well-suited instrument for the economic and highly accurate determination of vertical deflections. During an extensive test period from 2003 to 2004 the TZK2-D has been used for vertical deflection measurements at 87 stations in several field projects in Northern Germany and Switzerland. First results from a regional campaign in the Swiss Alps are presented as well as results from a high-
resolution local geoid profile determination and experiences using the system. The campaigns show that the system TZK2-D can be applied for the economic observation of 8 or more stations per night. The results obtained are promising since they demonstrate the potential of astrogeodetic measurements for high-resolution and high-precision determination of the fine structure of Earth’s gravity field in local areas. Sampling the gravity field with densely arranged stations, the system TZK2-D can meet high accuracy requirements in geophysical and engineering projects. Furthermore, the system can be applied for the local high-resolution validation of gravity field models and for the
fast determination of geoid profiles in limited or geodetically undeveloped areas