Computing the elevations/normal heights of the Bulgarian highest mountain peaks in EVRS, realization 2007
21/09/2016 | 17:15 | Session 5: Height systems and vertical datum unification
Author(s): Stanislava Valcheva and Lyubka Pashova
Stanislava Valcheva and Lyubka Pashova
The introduction of the European Vertical Reference System (EVRS) in Bulgaria in July, 2010 as a
reference for the heights, makes it necessary to reprocess most of the Bulgarian geodetic data. The
current study presents the assessed elevations of 10 of the highest mountain peaks of Bulgaria in
the EVRS, realization 2007.
In general, obtaining the height of a point in EVRS could be easily done by applying the
transformation parameters between the EVRS and the Baltic height system; the latter was used for
more than 60 years as height reference system in Bulgaria. However, the heights of some of the
Bulgarian mountain peaks like Musala, Vihren and Botev still refer to the older Black Sea height
system established in Bulgaria in 1931 and in use until the early 50es. Calculating the elevations of
these mountain peaks in EVRS could not be done directly through the height transformation
parameters given on the Coordinate Reference System in Europe (CRS-EU) website, for example. It
would require some extra effort taking into account the different height types between the Black
Sea height system and the EVRS (normal-orthometric versus normal height), as well as the different
datums and reference ellipsoids used for defining the normal gravity field. Considering all of the
above the estimated elevations in EVRS compared to the currently known values of the 10 mountain
peaks are changing by 14 cm to 36 cm.
In addition, the elevations (namely, the normal heights) of all 10 peaks in EVRS were also evaluated
by means of their height anomalies. The latter were obtained using two high resolution global
geopotential models (GGMs): EGM08 and EIGEN-6C4, and accounting for the terrain effects (via
classical integration of prisms and high resolution digital elevation model on a 3" × 3" grid: STRM
ver.4.1). The results show general agreement; however, a few values have larger uncertainties due to
the sparse gravity data used for the modelling computation. The difference of about 35 cm between
the two GGM related normal heights displays that the improvement in the local gravity field
representation is due to the contribution of the GOCE satellite gravity data in the EIGEN-6C4 GGM.
Comparing the GGM related heights to the GPS/leveled heights (now in EVRS) we also found that
there is a systematic error of 11.5 cm that is still present between the GGM and GPS/leveling data;
this error should be carefully considered for local geoid/quasigeoid computations in the future. At
the end particular differences between the GGM and GPS/leveled normal heights for every
mountain peak are discussed.