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Turkish Sea Level Monitoring System (TUDES)
Recently released Intergovernmental Panel on Climate Change (IPCC)'s Fourth Assessment Report (AR4) estimates that the global sea level will rise between 18 to 59 cm in the next century due to global climate change, global warming and melting of ice sheets. Rising sea levels change vertical datums, inundate wetlands and other low-lying lands, erode beaches, intensify flooding, and increase the salinity of rivers and groundwater tables. However, climate models, satellite data and hydrographic observations demonstrate that sea level is not rising uniformly around the world. Depending on the region, sea level has risen several times the global mean rise, or has actually fallen. Therefore, studies concerning the determination of the rate of sea level changes at global, regional, and local scales as well as the physical factors that contribute to the observed variability of sea levels have increased greatly than ever before, since they may have strong impacts on coastal ecosystems and human societies.
Many coastal countries deploy and operate tide gauges along their coasts to meet sea level related practical and scientific needs. Sea level data have been obtaining from various kinds of tide gauges located at the coasts of world oceans and seas for more than a hundred years. The first devices were simply graduated markings inscribed on rocks at the entraces to harbours, with sea level made visually. Only in the 1830's did the first mechanical gauges appear in near to modern form, equipped with clocks and chart recorders with a stilling well. Today, relative sea level measurements are carried out by the modern instruments, such as acoustic gauges with sounding tubes or in the open air, radar gauges operating in microwave spectral band the principle of which is measuring the time of flight of a pulse of radar rather than acoustic sound, and pressure gauges which measure the hydrostatic pressure of water column above a fixed pressure point and convert this hydrostatic pressure into sea level equivalent after correction for water density and gravity.
|Visual observation by marking on rocks
||Visual observation by tide staff
||Float operated tide gauge
|Marmara Ereğlisi Radar gauge/Turkey
Sea level observation stations (tide gauges) in Turkey are deployed and operated by General Directorate of Mapping in order to determine the geodetic vertical datum precisely that is indispensible for mapping activities and meet the sea level related defence and development requirements of the country. Sea level observations have been carried out by float operated gauges till 1998, since then the gauges have been upgraded and changed with acoustic ones with sounding tubes and Turkish National Sea Level Monitoring Sytem (TUDES) has been established. At present TUDES consists of one data center and 20 digital and automatic tide gauge stations given below:
TUDES is one of the unique tide gauge network at the Eastern Mediterranean and the Black Sea in which instantaneous sea level and some meteorological parameters such as temperature, pressure and wind are measured, stored digitally and transmitted to data center via automatic systems.
On March 2016, TUDES Web Portal was created to provide sea level data to the users effectively. With the use of the portal, accessing sea level data at the local datum has been freely opened to users. Users can also reach the sea level data at the national height datum after paying a standard annual subscription fee.
TUDES Web Portal:
Since sea level changes are the main indicators of global climate change due to global warming, sea level data have gained importance in oceanographic and meteorological studies for the investigation of the causes and the impact of climate change. In addition, tide gauge sea level data are used as a dataset that is complementary to seismic and geophysical measurements for the tsunami early warning systems.
General Directorate of Mapping provides sea level data and has a close collaboration with Boğaziçi University Kandilli Observatory and Earthquake Research Institute in the “Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North Eastern Atlantic, the Mediterranean and Connected Seas (ICG/NEAMTWS) Project”.
Through TUDES project, General Directorate of Mapping aims to;
- Determine and improve vertical reference surfaces for heights and depths used in topographic, nautical and aeronautical charts,
- Connect the vertical datums of Anatolia, Thrace, Turkish Republic of Northern Cyprus and the other Turkish islands,
- Test the Turkish Geoid at tide gauges,
- Monitor sea level variations in time and space domain,
- Find out tidal characteristics and produce accurate tide information,
- Provide sea level data for natural hazards such as eartquake, tsunami, storm surges, and climate change studies.
Sea level, atmospheric pressure, air temperature, relative humidity, wind speed and direction are measured with high accuracy at TUDES tide gauges and stored in dataloggers every 15 minutes interval. Data stored in dataloggers at tide gauges are transmitted to data center via GPRS. Collecting data from TUDES gauges, quality control and analysis processes are performed at the data center in Ankara.
- Sea level
- Atmospheric pressure
- Air temperature
- Relative humidity
- Wind speed
- Wind direction
Since the tide gauges measure sea level relative to land upon which they are located, observed sea level contains true sea level along with any vertical land movement signal (land subsidence or land uplift). Periodic geodetic measurements such as GPS, continuous GPS, and precise levelling are carried out at all TUDES tide gauges at 1-2 years interval to separate vertical land movements from true sea level and to monitor absolute sea level relative to earth center.