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| Titel |
Astro-geodetic Measurements using Digital Zenith Camera System in Istanbul-Turkey |
| VerfasserIn |
Kerem Halicioglu, Haluk Ozener, Rasim Deniz |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250056675
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| Zusammenfassung |
| The determination of earth’s gravity field and its change as a function of time is a major
problem in geodesy and geophysics. Recently, there have been many theoretical and applied
researches, which focus on geoid determination as a main reference surface (datum).
Astro-geodetic technique is one of the oldest and the most fundamental technique
used for geoid determination. Restrictions in direction measurements with analog
instruments, and time measurements decreased the usage of this method. However, tilt
measurements, UTC synchronized time measurements, and CCD technique made
significant developments in astro-geodesy, which are aimed to make improvements in
measurement accuracies. Hence, astro-geodetic measurements remove the restrictions of
gravity measurements in mountainous regions and coastlines. From this point of
view, with its suitable topography Turkey is an ideal test area for measurements as
such.
Researches on astro-geodetic geoid determination techniques using Digital Zenith
cameras are published by some universities around Europe (Vienna TU, IfE Hannover, ETH
Zurich, and AGH-UST in Poland) in the last decade. These various zenith camera
systems equipped with CCD sensors for imaging stars near zenith and with GPS
devices to obtain ellipsoidal coordinates and precise time in order to determine
the direction of the plumb line. These systems are designed and tested either for
insufficiency of conventional techniques or for the essential high precision astro-geodetic
measurements.
In the scope of this study, a new CCD equipped telescope is designed as Zenith Camera in
order to perform astro-geodetic observations in Istanbul. The system contains a CCD camera,
Schmidt-Cassegrain type telescope with 14 inches aparture, two inclinometers, a dual
frequency geodetic GPS receiver used for time measurements and ellipsoidal coordinates of
station, and a computer control unit for data capturing and system control. This new Digital
Zenith Camera system is capable of capturing stars up to approximate apparent magnitude of
18.5. Yet, the long aperture of optical component of Zenith Camera limits the image
dimensions on the celestial sphere which is 14’x21’=0.81deg2 (FOV) for 22.3 x
14.9 mm (4.7μm pixel size which is equal to an angular scale of 0.18”) sensor
size.
First observations are performed in Kandilli Observatory and Earthquake Research
Institute and the performance of capturing stellar objects is tested. Two different kinds of
CCD cameras are used in different observation epochs with different exposure times. Further
studies are going to be carried out on performing photogrammetric camera calibration
using stellar objects and on increasing leveling accuracy of the system with precise
inclinometers.
In this presentation, the different stages of the first observations of Digital Zenith Camera
System of Turkey will be evaluated. Those stages include the design, the field works, data
capturing, and data processing steps. In line with the shared experiences, future studies will
be questioned and discussed in order to achieve the necessary higher precision in
astro-geodetic observations. |
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