Abstract
We present the first high-precision astrogeodetic vertical deflection (VD) observations collected in Istanbul, Turkey, using a novel lightweight total station integrated with a charge-coupled device (CCD) camera, the QDaedalus system. The observed VDs are unique in that, they were measured for the first time in Istanbul, and they form Turkey’s first dense astrogeodetic network. To establish the Istanbul Astrogeodetic Network (IAN), we selected 30 benchmarks (BMs) with known geodetic coordinates. A total of 21 of these BMs are located in the coastal zone allowing us to investigate the quality of global gravity field models (GGFMs) along the coast of Istanbul. The standard deviations for our VDs are approximately ±0.20″which is commensurate with the VD accuracy of early studies assessing the QDaedalus observations. In particular, dedicated comparison measurements were conducted in two geographic regions—Munich and Istanbul—to control the accuracy of the VD measurements. Our new VD data set within the IAN was compared with predicted VDs from the Global Gravity Model plus (GGMplus) and the Earth Gravitational Model 2008 (EGM2008). The VD residuals between the QDaedalus observations, and predicted values from GGMplus and EGM2008 models tend to increase towards the coastlines, where discrepancies of several arcseconds were found. At 15 coastal BMs, the residuals in the N-S components exceed 2″ and reach values as large as 6″ while residuals in the E-W components exceeded 2″ at 3 BMs. We interpret these large differences as an indication of the current weaknesses in the GGF Ms, most likely reflecting errors in the altimetry-derived marine gravity measurements, which have been incorporated in the EGM2008 and GGMplus models, or the lack of coastal terrestrial gravity measurements, or both. We conclude that the astrogeodetic VDs observed by the QDaedalus are invaluable for independently assessing the quality of coastal-zone terrestrial gravity data sets and GGFMs.
| Original language | English |
|---|---|
| Pages (from-to) | 306-329 |
| Number of pages | 24 |
| Journal | Studia Geophysica et Geodaetica |
| Volume | 64 |
| Issue number | 3 |
| DOIs | |
| Publication status | Published - 1 Jul 2020 |
Bibliographical note
Publisher Copyright:© 2020, Inst. Geophys. CAS, Prague.
Funding
M.A. and C.H. would like to acknowledge the support of the German Academic Exchange Service (DAAD) short-term grant and the Scientific and Technological Research Council of Turkey (TUBITAK) BIDEB 2214-A grant program (1059B141601200, Albayrak and Hirt, 2018). C.H. would like to acknowledge Prof. Carl Christian Tscherning’s advice on the potential usefulness of vertical deflections to investigate and reinforce gravity field models in coastal zones, made in a conversation 19 years ago. M.A. and C.K.S. are grateful to the Fulbright Foundation for its support which enables data analysis in this study at the Ohio State University. The fieldwork in Istanbul was supported by the TUBITAK project (Grant Number 115Y237; Özlüdemir, 2015). The authors are grateful to their invaluable supporters: Burak Basoglu, Mohammed Mohseni Aref and H. Feriha Albayrak in Istanbul, and Markus Hauk and Paul Duckeck at TUM, Germany. The research is partially supported by the Natural Science Foundation of China (41584016, 41974040). This paper is a part of M.A.’s PhD thesis (619803) at ITU. Finally, the authors would like to thank the two anonymous reviewers and the editor for their constructive comments. Figures 3, 4 and S.2 were drawn using the Generic Mapping Tools (GMT; Wessel et al., 2013), and Fig. S.1 was drawn using QGIS (OpenStreetMap, 2019). M.A. and C.H. would like to acknowledge the support of the German Academic Exchange Service (DAAD) short-term grant and the Scientific and Technological Research Council of Turkey (TUBITAK) BIDEB 2214-A grant program (1059B141601200, Albayrak and Hirt, 2018). C.H. would like to acknowledge Prof. Carl Christian Tscherning’s advice on the potential usefulness of vertical deflections to investigate and reinforce gravity field models in coastal zones, made in a conversation 19 years ago. M.A. and C.K.S. are grateful to the Fulbright Foundation for its support which enables data analysis in this study at the Ohio State University. The fieldwork in Istanbul was supported by the TUBITAK project (Grant Number 115Y237; Özlüdemir , 2015). The authors are grateful to their invaluable supporters: Burak Basoglu, Mohammed Mohseni Aref and H. Feriha Albayrak in Istanbul, and Markus Hauk and Paul Duckeck at TUM, Germany. The research is partially supported by the Natural Science Foundation of China (41584016, 41974040). This paper is a part of M.A.’s PhD thesis (619803) at ITU. Finally, the authors would like to thank the two anonymous reviewers and the editor for their constructive comments. Figures 3, 4 and S.2 were drawn using the Generic Mapping Tools (GMT; Wessel et al., 2013), and Fig. S.1 was drawn using QGIS (OpenStreetMap, 2019).
| Funders | Funder number |
|---|---|
| Fulbright Foundation | |
| Markus Hauk | |
| Ohio State University | |
| International Technological University | |
| Deutscher Akademischer Austauschdienst | |
| National Natural Science Foundation of China | 41974040, 41584016, 619803 |
| Türkiye Bilimsel ve Teknolojik Araştirma Kurumu | 115Y237, 1059B141601200 |
Keywords
- QDaedalus
- astrogeodetic measurements
- coastal-zone geodesy
- satellite gravity
- vertical deflections