Preliminary Results on Quasi-Geoid for Western Part of Latvia Using Digital-Zenith Camera and DFHRS V.4.3 Software.

This research presents a quasi-geoid model for the Western part of Latvia based on parametric modelling of continuous polynomial surface by DFHRS (Digital Finite-element Height Reference Surface) software v.4.3 developed by Hochschule Karlsruhe - University of Applied Sciences. Apart from standard observations for quasi-geoid determination - GNSS/levelling points and Global Geopotential Models (GGMs), new kind of measurements - astrogeodetic vertical deflection (VD) observations provided by Digital Zenith Camera (DZC) are used. This instrument has been developed by the Institute of Geodesy and Geoinformatics, University of Latvia (GGI) and provides the accuracy of about 0.10 arcsec, what equivalent to 0.5 mm error in elevation for 1 km length and it gives two times better accuracy than 1st order levelling in Latvia respectively. 44 1st order GNSS/levelling points were observed by GGI staff and 27 1st order levelling points were provided by Latvian Geospatial Information Agency (LGIA), though 12 points were excluded from the processing, because of gross errors; 10 2nd order GNSS/levelling points and 98 points of terrestrial VD observations were also observed by GGI. The research presents the results on different solutions of quasi-geoid in Kurzeme region, using different types of data and the common principle of DFHRS software is also included. [ABSTRACT FROM AUTHOR]