Proceedings of the Institute of Geodesy and Cartography - No 111, Vol. LIII
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Jan Kryński
Centimetre geoid in Poland – reality and perspectives
Geodetic, gravimetric, astronomical, geological and satellite data acquired in cooperation of national and foreign research centres within the project supported by the Polish State Committee for Scientific Research in 2002–2005 have been extensively qualitatively and quantitatively analysed. They have been transformed to unified reference systems in accordance with recent standards, and then archived in the respective databases. The analyses performed indicated global geopotential models recently most suitable for quasigeoid modelling in Poland with the use of “remove-compute-restore” method. Methodology for computing terrain corrections with the use of available data was developed. Terrain corrections were calculated for point gravity data from the gravity database. A new set of mean 1' × 1' Faye gravity anomalies was generated. The acquired data was further used for generating models of astro-geodetic geoid, and precise models of gravimetric, GPS/levelling, integrated quasigeoid and quasigeoid best fitted to the heights of the sites of the POLREF network. Quality of quasigeoid models developed was estimated with the use of internal accuracy analysis as well as data from the control GPS/levelling traverse established within the project. Accuracy of the best of obtained quasigeoid models in Poland is at the level of 2 cm.
The elaborated methodology as well as the acquired and unified data should in the nearest future be used for developing a new quasigeoid model for Poland that would replace the GUGiK 2001 quasigeoid model, recommended by the Head Office of Geodesy and Cartography in Poland for the use in surveying practice. An extensive verification of gravity and height data, more rigorous and precise determination of terrain corrections with the use of all available information, the use of the results of adjustment of 1999–2002 levelling campaign, the integrated use of deflections of the vertical with gravity data, further improvement of methodology and computational techniques and the use of new global geopotential models from gravity field modelling-dedicated space missions GRACE and GOCE can contribute to substantial improvement of quality of quasigeoid models in Poland. The basic problem with generating a quasigeoid model of centimetre accuracy in Poland, best fitted to GPS/levelling data is an insufficient quality of heights of fitting stations of the POLREF network, that is estimated at the level of 3–4 cm.
Elżbieta Welker
Changes of Earth’s magnetic field in the period 1980–2005 on the basis of changes of its two selected elements
Magnetic field observed on the surface of Earth is the sum of fields formed by inner sources located in Earth’s nucleus and crust as well as by outer sources existing in ionosphere and magnetosphere. This field is subject to continuous changes characterised by different frequencies, from fractions of seconds till hundreds of years. Log-term changes, called secular changes, cannot be described in mathematical form; knowledge on these changes is indispensable for development of Earth sciences. On the basis of two selected elements of Earth’s magnetic field – declination D and vector of total intensity F – change of magnetic field was presented on the territory of Central Europe. The study was based on data collected from European observatories and on available data from secular points of Europe and points of magnetic survey. In addition, IGRF model computed in 5-year’s cycle by NASA, was used for the analysis. Changes of the selected components of Earth’s magnetic field were presented using spatial models prepared with 5-year’s frequency and with the help of graphs. Graphs were prepared using profiles, which cross Europe in west-east and north-south direction, starting from geophysical observatory in Belsk, assumed as base observatory. Both results obtained from analysis of changes of spatial models and those revealed on graphs indicated, that changes of elements of magnetic field in the studied period – 1980–2005 – have incidental character. Additionally, on the basis of data from measurements impact of method of extrapolation on results was studied and probable errors were calculated. As a result of analysis linear method of extrapolation can be assumed as the most accurate for period longer than three years. The expected error can be comparable to mean annual change and for longer period it can be even two times larger.
Knowledge concerning secular changes of magnetic field of Earth is used by surveyors, geophysicists, in navigation and in military service. As an example of using these changes the map of magnetic declination of Europe, prepared for 2006.5 epoch, can be mentioned.
As a result of this work it was confirmed, that continuous examination of geomagnetic field and systematic measurements within networks of secular points in Europe are necessary. In addition, discrepancies between data from IGRF model and data from measurements within anomaly regions were demonstrated. These discrepancies can reach 2–3 degrees, which disqualifies IGRF global model as a source material for detailed and local studies.
Grażyna Kloch, Jan Kryński
Quality assessment of terrain corrections „1992” and the analysis of their usefulness for the determination of terrain corrections with an accuracy required for precise geoid modelling
Terrain corrections „1992” were calculated for 27% of gravity stations in Poland using terrain slopes data surveyed in the vicinity of each gravity point (inner zone) and data from topographic maps (middle and outer zone) within the radius of 22.5 km. Unfortunately very little archive records on the subject survived. With few exceptions only the final values of terrain corrections „1992”, i.e. the total contributions of all three zones are available.
Low resolution of height data used, limitation of the maximum radius of terrain correction computation to 22.5 km around gravity station, the use of different algorithms and probably different standards substantially affect the quality of terrain corrections „1992”. As a result, the accuracy of terrain corrections „1992” is lower than the one required for modelling geoid at centimetre level of accuracy.
The authors of this paper made an attempt at investigating the usefulness of the terrain corrections „1992” (the total contribution of tree zones or the recovered contribution of the individual zones) for improving the quality of newly calculated terrain corrections, that will be used for modelling geoid with centimetre accuracy. Investigations based on analysis of the results of numerical tests conducted with use of the survived data records from PBG (Geophysical Exploration Company). The records contain the contributions of the inner, middle and outer zone to terrain corrections for 3327 gravity stations in Babia Gora area (gravity survey in Western Carpathians 1975).
First, the relation between terrain corrections „1992” and terrain corrections from PBG records has been determined. Then, the possibility of computing precise terrain correction in the inner zone with the use of DTM of 1" × 1" resolution – called DTED2 was analysed, and the possibility to recover the contribution of the inner zone as a difference between terrain correction from data base „1992” and re covered contributions of middle and outer zones were investigated. The effects of height data type (levelled height or height obtained from the topographic map) as well as resolution of DTM used on terrain correction in the middle and outer zone as well as the effect of resolution of DTM on whole terrain correction within the radius of 22.5 km were investigated.
Jan Ziobro
Precision and reliability of measurements of projection centersin real aerotriangulations
Correctness of network adjustment depends on selection of proper functional and statistical model and on eliminating mistakes and gross errors. Fulfilment of these conditions for aerial triangulation can be troublesome, as it involves even four groups of observations, different in character and origin. These groups are sometimes characterised by different precision of measurement, having often only roughly determined mean errors and variable levels of reliability of network observations. It makes more difficult correct weighting of observations and detection of gross errors. Above described problem is particularly related to measurement of projection centers, as observers often report mean error roughly or did not give it at all. The aim of this study was to determine precision of measurement of projection centers obtained in real blocks. The second goal of the work was to estimate reliability of this group of measurements in aerial triangulations for three scales of aerial photographs.
The study was based on renewed data preparation from production blocks, strictly obeying conditions of correctness of adjustment. Adjustment was preceded by pre-adjustment detection of gross errors and bad assignment of measurements into GPS profiles, using method prepared by the author. Production results were derived from various measurement systems and adjustment softwares; they were characterised by numerous imperfections concerning functional and statistical model, which were generally caused by the applied technologies. 25 blocks were selected for testing, applying three scales of aerial photographs: 1:13 000, 1:19 000 and 1:26 000, most frequently used in our country. Appearance of measurement of projection centers (on the average for 90 % of photographs in the block) was the second, important feature of these blocks. Number of photographs in blocks varied from 136 to 3402, and total number of photographs in all blocks was about 30 000.
Verified mean errors a priori, obtained from 25 adjustments, reach on the average 10.7 cm and standard deviation is 4.1 cm.
Analysis of global internal reliability of measurement of projection centers for particular scales revealed, that in blocks of photographs at a scale of 1:13 000 average redundancy component reached 0.50 for X, 0.48 for Y and 0.75 for Z. So, it can be concluded, that reliability of measurement of projections centers in these aerial triangulations was sufficient. For these blocks mean residual for all three coordinates of projection center reached 76 % of the average mean error a priori. For scales 1:19 000 and 1:26 000, in 9 out of 15 blocks redundancy component of horizontal coordinates of projection centers was lower than 0.25. Sufficient level of reliability was obtained only for one block. Average residual of horizontal coordinates was only ca. 56 % of mean error a priori.
Albina Mościcka, Małgorzata Brzezińska
Methodical basis for creating index of geographical namesexisting in Old and New Testament
Authors present in the article one of the research problems undertaken within the project tilted: „Concept of complex spatial-temporal information system on events and historical sources – Bible region case”. Methodical basis for creating one part of this system – index of geographical names appearing in Bible – was shown in the present work.
In the course of research works within this task the detailed analysis of geographical names existing in Old and New Testament was done. Analyses were conducted taking into account both context, in which geographical names are used, as well as way of entering to database geographical features, described by these names. As result of analyses it was decided to prepare index of geographical features, which will be accompanied by names with many other supplementary types of information. Such solution will enable to collect simultaneously in the database both names related to geographical features and features themselves, thus ensuring relations between them, temporal reference and spatial situation of these features.
Authors present in the article method of classification, rules of collecting names and geographical features entered to the database, as well as propose list of attributes accompanying each feature.