The second high-accuracy leveling network consists of permanently stabilized and accessible fundamental and working benchmarks. Fundamental benchmarks are approximately evenly distributed throughout the Serbian territory at an average distance from 20km to 50km, and the entire network geometry relies on them. The NVT2 working benchmarks classes are the main and auxiliary. They are distributed at distances of less than 1.5km in the form of leveling lines. The mean Adriatic Sea level observed by NVT2 tide gauges for the 1971.0 reference time epoch coincides with the vertical position of the quasigeoid reference surface. The NVT2 normal heights are implemented as a fiducial reference in the Serbian vertical transformation model for the height anomalies interpolation from the SQM2011 quasigeoid model during the spatial coordinates conversion. The NVT2 system is also used for height conversion to the Precise leveling network datum due to systematic tide gauges differences between those height references. This transformational concept is available as an official model in the GRIDER web application of the Republic geodetic authority.
The second high-accuracy leveling network was designed in 1967 and was measured in the period from 1970 to 1973. The geodetic datum of the NVT2 network was originally determined by minimizing the mean sea level trace detected by the network of tide gauges distributed in the Balkan coastal cities of the eastern coast of the Adriatic basin: Kopar, Rovinj, Bakar, Split-Marjan, Dubrovnik and Bar. The total number of NVT2 benchmarks was 4292. It is important to note that geodetic datum of the new Serblian reference leveling network (RNM) is defined by the normal heights of a selected subset of positionally reliable NVT2 fundamental benchmarks that are adopted as absolutely accurate in 1D adjustment.
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