The project aim and justification:

The objective of the project is to supply the Latvian economy with a widely applicable high precision gravity field anomalies model for the Latvian land and sea territories.The gravity field anomalies model is named geoid model. Geoid is the equipotential Earth gravity field surface which continues the mean sea level on the land and depicts the distribution of layers and minerals below the ground and below the sea as well. It is vital necessity to have an information on the height of the geoid above the mathematical surface of Earth ellipsoid in each particular site for the Global Navigation Satellite System’s (GNSS) application in economy for high precision normal height determination. GNSS denotes GPS, Galileo, GLONASS, etc. The geoid information will supply the meaningful contribution to the smart specialization strategy, for reaching the aims of the applications in smart technologies of national economy, as well as to the manpower development in research and technologies, for the know-how to PhD and master degree students at the University of Latvia and at the other universities. The GNSS technologies application will serve for competitive capacity in many branches of national economy:  geology, civil engineering, road construction, geodesy, land surveying, in maritime navigation safety and increased competitiveness for Latvian transit. The high precision gravity field model will access the studies of mineral deposits, the acquisition of smart materials and will increase the availability to develop new facilities in engineering.

The problem and its solution description:

In spite of the fact that the Global Navigation Satellite Systems (GNSS) are widely used for positioning in everyday life, however, the precision quality of height component is difficult. Usually the normal height has been used for engineering technologies. The normal heights in two different sites will surely show the water flow direction. The GPS determined ellipsoidal heights are quite a different from normal heights (difference 19-25 m from normal height values in Latvia). The global gravity field models can be used to reduce the ellipsoidal height to normal one, however, the precision doesn’t satisfy the engineering accuracy requirements. The former gravitation field anomalies model LV98 was developed in 1998 and it was used for GNSS determined ellipsoidal height reduction to Baltic 1977 (BAS77) height system with a precision 7-8 cm on the land. Currently the LAS’14 height system has been used which is the realization of the European EVRF2007 datum in Latvia.  The LV’14 quasigeoid model had been developed in Latvia over the land only for the reduction to LAS’14 normal height with precision 3-4 cm. The Latvian maritime charts are still based on the Soviet BAS77 datum. The investigation of the gravity field over the sea would access the possibility to develop the increased precision maritime charts in Latvia based on the European datum.  This could lead to the increased safety by using the GPS for navigation. This could increase the competitiveness of Latvian harbours. However, it is necessary to have a good quality gravity field studies on the land in order to achieve good quality geoid model over the sea, and otherwise.

In 2015 the Institute of Geodesy and Geoinformatics (LU GGI) successfully developed one cm precision quasigeoid model in Latgale and Vidzeme regions of Latvia (Project Nr 2014/0039/2DP/ Such a precision had not been achieved in Latvia before and these data will be useful for the normal height determination in those regions. It could be possible to make additional measurements in order to merge the geoid of Latgale and Vidzeme regions together with other part of land and of sea. Particularly important will be the vertical deflection measurements over the sea coast, in regions over the boundaries of Latvia as well as on the various gravity anomalous sites. The digital zenith camera had been developed and successfully tested at the LU GGI. The measuring precision of the vertical deflection is 0.1 arcsec and these measurements will strengthen the solutions obtained from both the gravity and dense GNSS/levelling data sets. Currently the improved DFHRS software programme is completed in Karlsruhe in cooperation of GGI researcher K.Morozova and professor R.Jaeger.  Similarly, like inprevious project the Bernese 5.2 software programme will be used according the EUREF recommendations in IGS08 reference system by using IGS/EPN base stations and LaatPos as well. The airborne gravity measurements over the sea will be used as well as satellite altimeter measurements from missions of Envisat, Sentinel-3 and Jason-2.