Abstract.One of the potential dangers that might arise as a result of bringing excessive amounts of groundwater to the surface of the Earth is land subsidence. Such surface deformations -these velocities may vary from a few millimetres to a few metres per year -do the greatest damage to infrastructure facilities and buildings in residential units. Agricultural lands, in which excessive irrigation is performed, and densely populated cities are more likely to suffer from land subsidence. Konya Closed Basin (KCB), where a rapid groundwater withdrawal has been observed during the last 30-40 years, is faced with such a threat. In this study, the possibility of the occurrence of land subsidence, related to groundwater withdrawal for the KCB, is assessed and the geodetic studies conducted up to now, with the intention of identifying land subsidence, are introduced. The vertical displacements of between −12 and −52 mm/year have been detected through GNSS observations collected on the 6-point test network. The land subsidence phenomenon has been developing in the areas where the groundwater is extensively used for irrigation and daily life. The results support the findings derived from the historical leveling records and point out the need of an extended study based on both GNSS and InSAR techniques for spatial and temporal mapping of land subsidence in the KCB.

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There are mainly two different orbital information, namely broadcast ephemerides and IGS final ephemerides (IGS rapid, ultra rapid, predicted and final ephemerides) used in the GPS positioning. The broadcast ephemerides used in practice and real time are obtained through assessments derived from the observations from the USA GPS reference stations. Broadcast ephemerides are formed (depending on GPS week) from satellite information and the accuracies they provide are adequate in many GPS applications. On the other hand, several parameters (for example, information about gravity area, improved satellite orbit information, etc.) need to be known in order to attain high accuracy in engineering and geodetic applications. Final ephemeris information can be downloaded from the related web sites via the internet. In this study, Keplerian motion and Keplerian orbital parameters will be explained briefly and extensive information about ephemerides and numerical applications will be given. Within this scope, for GPS satellites, ECEF coordinates of the satellites were computed using the broadcast ephemerides. The coordinates computed by using broadcast ephemerides were compared with the coordinates obtained from the IGS final orbits.