Bogdan Ney was born on 3 February 1935 in Pinsk. After graduating from high school in Tarnow in 1952, he attended the AGH University of Science and Technology in Cracow, where at the Department of Mining Surveying he received his MSc degree in 1957. At the same faculty he obtained his PhD degree in 1963 and habilitation in 1977. Two years later he was awarded the title of extraordinary professor of technical sciences, and in 1989 – the title of full professor.

His scientific career started in 1957 at the AGH University of Science and Technology in Cracow working as an assistant at the Department of the Descriptive Geometry, which from 1960 he continued in the Department of Geodesy and Surveying Data Processing. In 1969–1974 he served as the deputy director at the Institute of Mining and Engineering Surveying of the AGH University of Science and Technology in Cracow. His scientific interest focused on the problems of errors in surveying measurements, adaptation of some statistical techniques to the needs of surveying and development of surveying calculation methods, and methods and techniques of inventory, implementation and control measurements in engineering and engineering surveying. In 1974 Bogdan Ney was transferred to the Institute of Geodesy and Cartography (IGiK) in Warsaw for the position of director of the Institute which he held until 1991. In 1986, he was elected a corresponding member of the Polish Academy of Sciences (PAS), and in 2002 a full member of PAS. As the director and then the head of the System Research Laboratory of IGiK he was further involved in research, providing valuable contributions in the following fields: the use of principles and techniques of aerial and satellite remote sensing in various fields of science and applications; general, organizational and economic problems of surveying and mapping as well as related disciplines; spatial information systems; scientific and scientific-technical policy. In 1991–1997 he continued his educational activity lecturing at the Military University of Technology. The entire scientific achievements of Bogdan Ney consist of more than 300 publications, and many presentations on national and international conferences and seminars. His was the author/coauthor of 24 monographs, 6 textbooks and many other scientific reports. He successfully supervised 10 PhD students.

Bogdan Ney had great achievements in organizational and social activities. He was active in numerous committees, councils, societies and associations. In 1998 the Agriculture-Technical Academy in Olsztyn honoured Bogdan Ney awarding him an honorary doctor degree. Bogdan Ney enjoyed widespread recognition of the scientific community due to his high culture, responsibility in carrying out numerous duties, supporting young scientists, outstanding ability to solve conflict situations and sincere kindness towards all people. He was not only a respected scientist and authority, but also a wonderful man, full of tact and warmth, admired and liked by colleagues. Professor Bogdan Ney, age 85, passed away in Warsaw, on 23 March 2020. He was one of the outstanding surveyors with wide reputation in the scientific community.

The summary of research activities concerning gravity field modelling and gravimetric works performed in Poland in the period of 2011–2014 is presented. It contains the results of research on geoid modelling in Poland and other countries, evaluation of global geopotential models, determination of temporal variations of the gravity field with the use of data from satellite gravity space missions, absolute gravity surveys for the maintenance and modernization of the gravity control in Poland and overseas, metrological aspects in gravimetry, maintenance of gravimetric calibration baselines, and investigations of the non- tidal gravity changes. The bibliography of the related works is given in references.

The summary of research activities concerning reference frames and reference networks performed in Poland in a period of 2011–2014 is presented. It contains the results of research on implementation of IUGG2011 and IAU2012 resolutions on reference systems, implementation of the ETRS89 in Poland, operational work of permanent IGS/ EUREF stations in Poland, operational work of ILRS laser ranging station in Poland, active GNSS station networks in Poland, maintenance of vertical control in Poland, maintenance and modernization of gravity control, and maintenance of magnetic control in Poland. The bibliography of the related works is given in references.

The GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) has significantly upgraded the knowledge on the Earth gravity field. In this contribution the accuracy of height anomalies determined from Global Geopotential Models (GGMs) based on approximately 27 months GOCE satellite gravity gradiometry (SGG) data have been assessed over Poland using three sets of precise GNSS/levelling data. The fits of height anomalies obtained from 4th release GOCE-based GGMs to GNSS/levelling data were discussed and compared with the respective ones of 3rd release GOCE-based GGMs and the EGM08. Furthermore, two highly accurate gravimetric quasigeoid models were developed over the area of Poland using high resolution Faye gravity anomalies. In the first, the GOCE-based GGM was used as a reference geopotential model, and in the second – the EGM08. They were evaluated with GNSS/levelling data and their accuracy performance was assessed. The use of GOCE-based GGMs for recovering the long-wavelength gravity signal in gravimetric quasigeoid modelling was discussed.

The dedicated gravity satellite missions, in particular the GRACE (Gravity Recovery and Climate Experiment) mission launched in 2002, provide unique data for studying temporal variations of mass distribution in the Earth’s system, and thereby, the geometry and the gravity field changes of the Earth. The main objective of this contribution is to estimate physical height (e.g. the orthometric/normal height) changes over Central Europe using GRACE satellite mission data as well as to analyse them and model over the selected study area. Physical height changes were estimated from temporal variations of height anomalies and vertical displacements of the Earth surface being determined over the investigated area. The release 5 (RL05) GRACE-based global geopotential models as well as load Love numbers from the Preliminary Reference Earth Model (PREM) were used as input data. Analysis of the estimated physical height changes and their modelling were performed using two methods: the seasonal decomposition method and the PCA/ EOF (Principal Component Analysis/Empirical Orthogonal Function) method and the differences obtained were discussed. The main findings reveal that physical height changes over the selected study area reach up to 22.8 mm. The obtained physical height changes can be modelled with an accuracy of 1.4 mm using the seasonal decomposition method.

Research activities of Polish research groups in a period of 2015–2019 on reference frames and reference networks are reviewed and summarised in this paper. The summary contains the results concerning the implementation of latest resolutions on reference systems of the International Union of Geodesy and Geophysics and the International Union of Astronomy with special emphasis on the changes in the Astronomical Almanac of the Institute of Geodesy and Cartography, Warsaw. It further presents the status of the implementation of the European Terrestrial Reference System 1989 (ETRS89) in Poland, monitoring the terrestrial reference frame, operational work of GNSS permanent IGS/EPN stations in Poland, operational work of the laser ranging station in Poland of the International Laser Ranging Service (ILRS), active GNSS station network for the realization of ETRS89 in Poland, validation of recent ETRS89 realization, expressed in ETRF2000 in Poland, and maintenance of the vertical control in Poland (PL-KRON86-NH). Extensive research activities are observed in the field of maintenance and modernization of gravity control not only in Poland, but also in Sweden and in Denmark, as well as establishment of gravity control in Ireland based on absolute gravity survey. The magnetic control in Poland was also regularly maintained. The bibliography of the related works is given in references.

Activities of the Polish research gSDroups concerning gravity field modelling and gravimetry in a period of 2015–2018 are reviewed and summarised in this paper. The summary contains the results of research on the evaluation of GOCE-based global geopotential models (GGMs) in Poland and geoid modelling. Extensive research activities are observed in the field of absolute gravity surveys, in particular for the maintenance of national gravity control in Poland, Sweden, Denmark, the Republic of Ireland and in Northern Ireland as well as for geodynamics with special emphasis on metrological aspects in absolute gravimetry. Long term gravity variations were monitored in two gravimetric laboratories: the Borowa Gora Geodetic-Geophysical Observatory, and Jozefoslaw Astrogeodetic Observatory with the use of quasi-regular absolute gravity measurements as well as tidal gravimeter records. Gravity series obtained were analysed considering both local and global hydrology effects. Temporal variations of the gravity field were investigated using data from GRACE satellite mission as well as SLR data. Estimated variations of physical heights indicate the need for kinematic realization of reference surface for heights. Also seasonal variability of the atmospheric and water budgets in Poland was a subject of investigation in terms of total water storage using the GLDAS data. The use of repeatable absolute gravity data for calibration/validation of temporal mass variations derived from satellite gravity missions was discussed. Contribution of gravimetric records to seismic studies was investigated. The bibliography of the related works is given in references.

The accuracy of computed terrain corrections might be an important issue when modelling precise gravimetric geoid, especially for evaluating the quality of geoid model developed. It depends on the accuracy of heights and positions of gravity points used and on the quality of digital terrain model applied. The work presents the attempts towards the estimation of the effect of uncertainty in height and position of gravity points as well as uncertainty of digital terrain model on the accuracy of computed terrain corrections. Analytical formulae for the respective error propagation were developed and they were supported, when needed, by numerical evaluations. Propagation of height data errors on calculated terrain corrections was independently conducted purely numerically. Numerical calculations were performed with the use of data from gravity database for Poland and digital terrain models DTED2 and SRTM3. The results obtained using analytical estimation are compatible with the respective ones obtained using pure numerical estimation. The terrain correction error resulting from the errors in input data generally does not exceed I mGal for Poland. The estimated accuracy of terrain corrections computed using height data available for Poland is sufficient for modelling gravimetric geoid with a centimetre accuracy.

The choice of global geopotential model used in remove-restore technique for determination of regional quasi geoid from gravity data may affect the solution, in particular when the accuracy is supposed to reach a centimetre level. Global geopotential model plays also an important role in validating height anomalies at GPS/levelling sites that are used for the estimation of the external accuracy of quasigeoid models. Six different global geopotential models are described in the paper. Three kinds of numerical tests with use of terrestrial gravity data and GPS/levelling height anomalies were conducted. The first one concerned comparison of height anomalies at GPS/levelling sites ia Poland with corresponding ones computed from various global geopotential models. In the second one the terrestrial gravity anomalies in Poland and neighbouring countries were compared with corresponding gravity anomalies computed from global geopotential models. Finally the quasigeoid models obtained from gravity data with use of different global geopotential models were verified against corresponding height anomalies at GPS/levelliag sites in Poland. Data quality was discussed and best fitting global geopotential model in Poland was specified.

An increased use of global navigation techniques for positioning, and in particular for height determination, led to a growing need for precise models of height reference surface, i.e. geoid or quasigeoid. Geoid or quasigeoid heights at a cm accuracy level, provided on growing number ofGPS/levelling sites, can not only be used for quality control of gravimetric geoid but they also can be integrated with gravity data for geoid/quasigeoid modelling. Such a model is of particular use for surveying practice. A method of quasigeoid modelling based on GPS/levelling data with support of geopotential model and gravity data was developed. The components of height anomaly are modelled with the deterministic part that consists of height anomaly based on EGM96 geopotential model and Molodensky's integral, as well as the polynomial representing trend, and from the stochastic part represented by the isotropic covariance function. Model parameters, i.e. polynomial coefficients and covariance function parameters are determined in a single process of robust estimation, resistant to the outlying measurements. The method was verified using almost a thousand height anomalies from the sites of the EUREF-POL, POLREF, EUVN'97 and WSSG (Military Satellite Geodetic Network) networks in Poland as well as geopotential model refined with gravity data in l' x l' grid. The estimated average mean square error of quasigeoid height is at the level of O.Ol m. The outlying measurements were efficiently detected.

Calculation of the effect of topography on the observed gravity becomes particularly important when modelling high-precision geoid. It requires a digital terrain model of appropriate resolution and accuracy. Various global, regional and local digital terrain models of different accuracy and resolution are recently available. Evaluation of the DTM used is required for verification and validation of its quality as well as for estimating accuracy of geoid model derived with considering the effect of topographic masses. Two DTMs: the SRTM3 of 3" x 3" resolution and the national DTM for Poland of l" x l" or l" x 2" resolution - called DTED2 - were evaluated with use of high-resolution local DTMs developed using digital photogrammetry of 25 m x 25 m as well as the regional model in Tatra mountains of 10 m x 10 m. Then the heights of almost 1000 GPS/levelling stations of Polish geodetic control were compared with the heights from the DTED2 model. The heights of over a million of gravity stations from gravity database, that were the basis of previous geoid modelling in Poland, were also compared with the heights from the DTED2 model. The effect of uncertainty of a DTM on estimation of mean gravity anomalies was discussed. In particular, the effect of replacing heights from gravity database with the heights from the DTED2 model in the process of calculating mean gravity anomalies, on the accuracy of geoid modelling was investigated. The use of the DTED2 model is at present recommended for determination of precise geoid model in Poland.

Modelling quasigeoid with centimetre accuracy requires taking into account irregularities of topography in the vicinity of a gravity station. i.e. the terrain correction w surveyed gravity. Accuracy of determination of the terrain correction affects quality of quasi geoid model determined. It depends on the resolution and accuracy of terrain data that usually is provided in the form of a digital terrain model DTM. Investigations were conducted with the use of the Digital Terrain Elevation Data - DTED2 model developed for Poland according to the NATO-STANAG 3809 standard, as well as global models SRTM3 and SRTM30 (The Shuttle Radar Topography Mission). Also height data from the gravity database was considered. The prism method of determination of terrain corrections was applied in majority of numerical tests. Practical method for determining the optimum radius of the integration cap considering roughness of topography as well as required accuracy of terrain corrections was developed. The effect of vertical and horizontal uncertainty of a DTM as well as its resolution on the quality of the terrain corrections was investigated. The terrain corrections obtained using a prism method were also compared with the respective ones calculated using the FIT approach. The usefulness of the available topography data for precise terrain correction computation in Poland was discussed. The results of the investigations were used to determining the strategy of computation of the terrain corrections to point gravity data in the gravity database for Poland. The "2005" terrain correction set calculated for I 078 046 gravity stations contributes to the increase of precision of gravimetric quasigeoid models developed for Poland.

Sea level monitoring at tide gauges plays an important role in geodesy, geodynamics research and oceanography. It provides data for referencing vertical datum, for modelling geoid in coastal regions, for determination of vertical land movements and for studying ocean dynamics. Investigation of Baltic Sea level variations ·is considered an important component of geodynamics research in Central and Northern Europe. The analysis of tide gauge records from Baltic sites was conducted in the framework of the project on a cm geoid in Poland. Those records showed strong common features that were further used for deriving the model of Baltic Sea level variations. High level of correlations of the model with individual site data proved its adequacy. Regional characteristics of the model were investigated using regression and correlation analysis. It was shown that the model represents very well both global and regional features of Baltic Sea level variations. The use of the model as reference to investigate local features of tide gauge records that reflect site-specific variations of sea level was also discussed. Spectral analysis of the model of Baltic Sea level variations indicates the existence of distinguished term of Chandler period besides two major terms of annual and semi-annual periods. The existence of polar motion component in Baltic Sea level variations was investigated using correlation analysis. Also the land vertical movement derived from Baltic tide gauge data was determined and compared with literature data.

Time series of weekly and daily solutions for coordinates of permanent GNSS stations may indicate local deformations in Earth’s crust or local seasonal changes in the atmosphere and hydrosphere. The errors of the determined changes are relatively large, frequently at the level of the signal. Satellite radar interferometry and especially Persistent Scatterer Interferometry (PSI) is a method of a very high accuracy. Its weakness is a relative nature of measurements as well as accumulation of errors which may occur in the case of PSI processing of large areas. It is thus beneficial to confront the results of PSI measurements with those from other techniques, such as GNSS and precise levelling. PSI and GNSS results were jointly processed recreating the history of surface deformation of the area of Warsaw metropolitan with the use of radar images from Envisat and Cosmo- SkyMed satellites. GNSS data from Borowa Gora and Jozefoslaw observatories as well as from WAT1 and CBKA permanent GNSS stations were used to validate the obtained results. Observations from 2000–2015 were processed with the Bernese v.5.0 software. Relative height changes between the GNSS stations were determined from GNSS data and relative height changes between the persistent scatterers located on the objects with GNSS stations were determined from the interferometric results. The consistency of results of the two methods was 3 to 4 times better than the theoretical accuracy of each. The joint use of both methods allows to extract a very small height change below the level of measurement error.

The existing Polish gravity control (POGK) established in the last few years of 20th century according to the international standards is spanned on 12 absolute gravity stations surveyed with four different types of absolute gravimeters. Relative measurements performed by various groups on nearly 350 points of POGK with the use of LaCoste&Romberg (LCR) gravimeters were linked to those 12 stations. The construction of the network, in particular the limited number of non homogeneously distributed absolute gravity stations with gravity determined with different instruments in different epochs is responsible for systematic errors in g on POGK stations. The estimate of those errors with the use of gravity measurements performed in 2007-2008 is given and their possible sources are discussed. The development of absolute gravity measurement technologies, in particular instruments for precise field absolute gravity measurements, provides an opportunity to establish new type of gravity control consisting of stations surveyed with absolute gravimeters. New gravity control planned to be established in 2012-2014 will consist of 28 fundamental points (surveyed with the FG5 – gravimeter), and 169 base points (surveyed with the A10 gravimeter). It will fulfill recent requirements of geodesy and geodynamics and it will provide good link to the existing POGK. A number of stations of the new gravity control with precisely determined position and height will form the national combined geodetic network. Methodology and measurement schemes for both absolute gravimeters as well as the technology for vertical gravity gradient determinations in the new gravity control were developed and tested. The way to assure proper gravity reference level with relation to ICAG and ECAG campaigns as well as local absolute gravimeter comparisons are described highlighting the role of metrology in the project. Integral part of the project are proposals of re-computation of old gravity data and their transformation to a new system (as 2nd order network) as well as a definition of gravity system as “zero-tide” system. Seasonal variability of gravity has been discussed indicating that the effects of environmental changes when establishing modern gravity control with absolute gravity survey cannot be totally neglected .

The article presents the reviewed and summarised research activities of Polish research groups on reference frames and reference networks in a period of 2019–2022. It contains the results on the implementation of latest resolutions on reference systems of the International Union of Geodesy and Geophysics and the International Astronomical Union focusing on changes in the consecutive issues of the Astronomical Almanac of the Institute of Geodesy and Cartography, Warsaw. It further presents the status of the implementation of the European Terrestrial Reference System 1989 (ETRS89) in Poland, monitoring the terrestrial reference frame, including research on global terrestrial reference frames, GNSS data analysis within the EUREF Permanent Network, research on GNSS receiver antenna phase centres, research on impact of non-tidal loading effects on position solutions, and on station velocities. Then the activities concerning the realization of ITRS and ETRS89 in Poland are discussed, including operational work of GNSS IGS/EPN stations as well as operational work of the laser ranging station of the International Laser Ranging Service, with special emphasis on the Polish active GNSS network for the realization of ETRS89 and maintenance of the vertical control network. Extensive research activities are observed in the field of implementation of the International Terrestrial Gravity Reference Frame in Poland, maintenance and modernization of gravity control network in Poland but also in Sweden, establishment of gravity control network in Ireland based on absolute gravity survey as well as maintenance of the national magnetic control network in Poland which is traditionally performed on a regular basis.

The article presents the reviewed and summarised research activities of the Polish research groups on gravimetry and gravity field modelling in the period of 2019–2022. It contains the results of absolute gravity surveys for the maintenance of the international gravity reference level in Poland and Europe, and for geodynamic research with an emphasis on metrological aspects. It also contains relative gravimetry issues as well as the results of marine gravity surveys in the southern Baltic Sea. Non-tidal gravity changes were extensively investigated. Long-term gravity variations were monitored at the Borowa Gora Geodetic-Geophysical Observatory and in a few other locations in Poland. The contribution of gravimetric records to seismic studies was investigated. Temporal variations of the gravity field from GRACE (Gravity Recovery and Climate Experiment) and GRACE-FO (GRACE Follow-On) data, in particular, deformations of the Earth’s surface as well as temporal variations of heights, total water storage and groundwater storage were investigated. Moreover, GRACE-based products and the performance of monthly Global Geopotential Models (GGMs) were a subject of research. GGMs developed in last years were evaluated. The research on developing new approaches in geoid modelling and their validation was conducted. New regional and local geoid models were determined for Poland and Ethiopia. The use of different techniques for estimating the absolute sea level at sites of the selected network in the Baltic Sea was investigated.