The deduction of a regularly spaced gravity anomaly grid from scattered survey data is studied, addressing mainly two aspects: reduction of gravity to anomalies and subsequent interpolation by various methods. The problem is illustrated in a heterogeneous study area and contrasting test areas including mountains, low terrains, and a marine area. Provided with realistic error estimates, Least Squares Collocation interpolation of Residual Terrain Model anomalies yields the highest quality gravity grid. In most cases, the Bouguer reduction and other interpolation methods tested are equally viable. However, spline-based interpolation should be avoided in marine areas with trackwise survey data.

In 2017 and 2018 GFZ performed two gravimetry campaigns on commercial ferries in the Baltic Sea. The nature of such “non-dedicated” campaigns is different from “dedicated” campaigns that are performed on research vessels with tracks planned according to gravity measurement needs. The non-dedicated campaigns use non-survey vessels or survey vessels running for other purposes such as hydrographic measurements, which may require additional corrections. To assess the usefulness of non-dedicated campaigns, we analysed gravity measurements collected on two commercial ferries as part of the EU funded FAMOS project. Besides the typical marine gravimetry corrections, we also investigated the corrections for the vertical accelerations due to the ship’s movement and the dynamical effect due to the cross-coupling between horizontal and vertical acceleration components. Taking the latter two corrections into account partly leads to slight improvements, but our results also demonstrate that the standard processing without the two corrections, as used in most of the dedicated campaigns, already delivers good quality end products that fulfil the requirements of a typical marine gravimetry survey with an uncertainty of about 1 mGal. Our findings suggest that gravimetry campaigns on commercial ferries can be used to complement dedicated marine gravimetry campaigns and contribute to geodetic purposes.

The present ETRS 89 realisations in Latvia and Lithuania are based on the EUREF‐BAL'92 campaign, which has an estimated accuracy of the same level as the original EUREF 89 campaign (class C). Latvia and Lithuania wish to replace their EUREF‐BAL'92 realisation with an ETRS 89 realisation based on the NKG 2003 GPS campaign. The NKG 2003 GPS campaign was carried out in GPS‐week 1238 (Sept 28th to Oct 4th 2003) under the framework of the Nordic Geodetic Commission (NKG). The campaign included mainly permanent stations in the Nordic and Baltic area as well as Island, Greenland and Svalbard. In Latvia, Lithuania and Denmark also field sites defining ETRS 89 were included. New ETRS 89 coordinates based on the NKG 2003 campaign have been calculated. The campaign resulted in a set of coordinates in ITRF 2000 epoch 2003.75. All stations in Latvia and Lithuania as well as a sub‐set of stations in neighbouring countries were converted to ETRS 89 using the standard procedure described by Boucher and Altamimi. No intraplate deformations have been taken into account, thus the epoch of the ETRS 89 coordinates is 2003.75. Estimated accuracy: 0,5–1 cm (95%) for the horizontal co‐ordinates and 1–2 cm (95%) for the vertical at the epoch of the observation. The computed ETRS 89 coordinates presented in this paper are to be considered as improvement and extension of ETRS 89 in Latvia and Lithuania based on the NKG 2003 GPS campaign. During symposia in Riga, 14–17 June 2006, the IAG Reference Frame Sub‐commission for Europe (EUREF) recognising, that in Sept‐Oct 2003 the EUREF‐NKG‐2003 campaign in Scandinavia and the Baltic countries was observed, including points in Latvia and Lithuania, and that the results of it were submitted to the EUREF Technical Working Group, where they were accepted as Class B standard (about 1 cm at the epoch of observation), endorses the subset of points submitted to the EUREF Technical Working Group as extension to the current realisation of ETRS89 (Resolution No 1). Keyword : EUREF, ETRS 89, GPS campaign, ITRF2000

The paper deals with a research in the area of automation of positional star observations. In order to fully employ recent progress in imaging technologies, star image recognition and reference star identification process should gain comparable level of automation. A software package for this purpose has been developed in the Institute of Geodesy of the University of Latvia. It is capable of near-real-time image processing, star identification and astrometric position determination.

Tide gauge observations provide sea level relative to the Earth’s crust, while satellite altimetry measures sea level variations relative to the centre of the Earth’s mass. Local vertical land motion can be a significant contribution to the measured sea level change.Satellite altimetry was traditionally used to study the open ocean, but this technology is now being used over inland seas too.The difference of both observations can be used to estimate vertical crustal movement velocities along the sea coast. In this paper, vertical crustal movement velocities were investigated at tide gauge sites along the Adriatic Sea coast by analyzing differences between Tide Gauge (TG) and Satellite Altimetry (SA) observations. Furthermore, the estimated vertical motion rates were compared with those from nearby GNSS measurements.The study determines the practical relationships between these vertical crustal movements and those determined from unrelated data acquired from the neighbouring GNSS stations. The results show general consistence with the present geodynamics in the Adriatic Sea coastal zone.

Over several years the Institute of Geodesy and Geoinformatics (GGI) was engaged in the design and development of a digital zenith camera. At the moment the camera developments are finished and tests by field measurements are done. In order to check these data and to use them for geoid model determination DFHRS (Digital Finite element Height reference surface (HRS)) v4.3. software is used. It is based on parametric modelling of the HRS as a continous polynomial surface. The HRS, providing the local Geoid height N, is a necessary geodetic infrastructure for a GNSS-based determination of physcial heights H from ellipsoidal GNSS heights h, by H=h-N. The research and this publication is dealing with the inclusion of the data of observed vertical deflections from digital zenith camera into the mathematical model of the DFHRS approach and software v4.3. A first target was to test out and validate the mathematical model and software, using additionally real data of the above mentioned zenith camera observations of deflections of the vertical. A second concern of the research was to analyze the results and the improvement of the Latvian quasi-geoid computation compared to the previous version HRS computed without zenith camera based deflections of the vertical. The further development of the mathematical model and software concerns the use of spherical-cap-harmonics as the designed carrier function for the DFHRS v.5. It enables - in the sense of the strict integrated geodesy approach, holding also for geodetic network adjustment - both a full gravity field and a geoid and quasi-geoid determination. In addition, it allows the inclusion of gravimetric measurements, together with deflections of the vertical from digital-zenith cameras, and all other types of observations. The theoretical description of the updated version of DFHRS software and methods are discussed in this publication.