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Poceedings of the Institute of Geodesy and Cartography - No 103, Vol. XLVIII

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Price: 32 PLN

Andrzej Sas-Uhrynowski
Leonid G. Kasyanenko

Maria Gruszczyńska (Budzyńska)
Estimation of soil moisture under cereals on the basis of ERS-2 SAR images recorded in C (VV) band
Among numerous methods only remote sensing offers a potential means of determining the spatial distribution of soil moisture over large areas within short time and at a reasonable cost. Among various electromagnetic bands available for remote sensing observations from satellite platforms, the microwave region offers the greatest potential in terms of penetration through soil to the depth dependent on spectral band - the longer band, the deeper penetration. Microwaves can penetrate clouds, which is important for regularity of observations. The main physical factors, which affect radar backscatter response, are surface roughness and dielectric properties of target, which closely correspond with the moisture content. The possibility to determine soil moisture using active microwaves draws the attention of scientists since the radar techniques have been open to civilians. It is obvious from the recent studies, that radar backscatering coefficient σo increases with the increase of soil moisture and surface roughness (Ulaby F.T. 1974). For soil moisture determination from radar measurements the effect of surface roughness should be separated from the effect of moisture (soil and vegetation moisture) of the target. It was found that vegetation surface roughness could be expressed by Leaf Area Index (LAI) values. LAI can be measured during field surveys or calculated from images obtained in optical bands of electromagnetic spectrum (Dąbrowska-Zielińska K. 1995). In this article author proposes the assessment of soil moisture for the stable vegetation surface roughness conditions characterised by LAI. and for the stable vegetation moisture conditions characterised by growth stage of crops. The method has been verified using the developed algorithms and ground truth data. The results show that the differences in measured and calculated soil moisture values are not significant and can be accepted in most of agricultural applications. In this article the results obtained for cereals from the study carried out from 1992 to 1997 at the test site in Wielkopolska region are presented.

Maria Dobrzycka, Jan Cisak
Polish Geodynamic Network, 0 – Epoch, 1997
Reflecting natural and man-induced tectonics the position of the network points do change in time. Their motion can be monitored by repetitive measurements using modern geodetic methods. According to current trends and international recommendations the so called geodynamic network was established in Poland, aiming at monitoring coherency and stability of the primary control network, contributing to regional and global geodynamic investigations and providing unified frame for local geodynamic programs. The geodynamic network was set up in the first half of 90-ties. It consists of 36 points. Most of them (33) were chosen from nearly 400 – points of primary network that was in the process of fundamental modernisation.  Location of points (Fig.1), consulted with geologists, gives coverage to main and subordinate crustal blocks. Monumentation of points (not fully uniform) is shown in Fig.2. The geodynamic network includes five permanent GPS stations of the “GPS Permanent EUREF Network” and seven remaining 0-order EUREF points, serving as an extension of ETRS system.
0-epoch GPS campaign in the Polish Geodynamic Network (PSG) was carried out in September 1997, in five three-day sessions, using eight sets of Leica receivers. The observations were processed and adjusted in co-operation with WUT Analysis Centre of the „GPS Permanent EUREF Network” program, using Bernese 4.0 software, according to presently valid standards. As the reference points served all five Polish GPS permanent stations, as well as five stations in neighbouring countries. Vectors used in adjustment are shown in Fig. 4. The results of 0 - epoch campaign were compared to those from former campaigns: EUREF-POL (1992) and POLREF (1994–1995). The differences obtained in latitude, longitude and ellipsoidal height are shown in Table 1 and illustrated in Fig. 5, in order to better indicate their systematic character that is especially significant in the height component.
Looking for reasons of such results several possible sources were considered, among them steadily changing, different ITRF frame parameters, used for elaboration of different campaigns (91 for EUREF-POL, 94 for POLREF and 96 for PSG), as well as different versions of computing program, methods of adjustment and ties selections. Special attention however, was paid to the antenna phase centre effect. In both POLREF (1994–1995) and PSG (1997) campaigns 8 Leica SR299 and SR399 receivers were used. At the reference points different sets of instruments were operating and different antenna characteristics were used: old and new, provided by manufacturers and recommended by IGS, model IGS 01/1996. Differences between old and new characteristics of the selected antenna types are shown in Table 2.
To test the validity of the antenna heights used in PSG measurements, two day's long GPS campaign on the Polish Standard Baseline Warszawa-Bemowo was conducted (see Fig.6), with use of the majority of GPS antenna applied in the PSG campaign. On the first day instruments were installed in direct while on the next day in the reverse order. Differences in calculated height and distance between each pair of antennas in both setting orders, were compared with standard values (accuracy better than 2mm, obtained from multiple precise EDM measurements and geometric levelling). The results shown in Table 3 may suggest erroneous value of height component for Leica and - smaller – for DM model T antenna phase centre, while four other antenna types show very good agreement.
Authors present one more possible source of discrepancies between results of different campaigns, reflected in rather regular, periodic variations of point positions. Not yet modelled, they are well documented by observations at permanent GPS stations (see Fig. 7) and possibly caused by not enough sufficient modelling of tidal effects. 
The reliable interpretation of results from different GPS campaigns is not easy, it needs very detailed information about instruments, methods and options of program used. Sometimes, when considering sophisticated tasks, re-computation might be appropriate.

Andrzej Sas-Uhrynowski, Eugeniusz Zanimonski, Aleksander Kostin
Examination and improvement of ballistic gravimeter TBG
Two field ballistic gravimeters were constructed at the Institute of Geodesy and Cartography in 1995 and 1996; they were given names TBG-95 and TBG-96 (Terrestrial Ballistic Gravimeter). Authors presented in the article description of gravimeter and principle of its work. They also discussed the results of research works, aimed at preparation of a method for decreasing the disturbing impact of autoseismic vibrations and seismic background, as well as influence of residual air particles in vacuum ballistic chamber on results of measurements, conducted in the field. The succeeding experiments were described; their results were presented graphically and analysed. It enabled to propose some solutions and procedures, leading to partial elimination of the above mentioned disturbances and to improvement of accuracy of measurements with TBG gravimeter.

Jerzy Janusz, Wojciech Janusz
Broken Base of Length for comparation of electronic distance meters
Since 40 years the Department of Geodesy, Institute of Geodesy and Cartography fulfils in Poland the role of metrological laboratory for comparation of electronic  distance meters.
Electronic distance meters should be checked periodically, in order to determine their real technical state and  corrections to their readouts. Such a verification is done through comparison of length measured by these instruments with standard lengths on the special test bases. In Poland test bases in the form of  group of ferro-concrete poles, with heads adjusted to centring distance meter and range reflector, are used; these poles are located in the fixed distances on the straight line, having 600 to 800 meters in length. It is difficult to protect such a long base, usually located in the terrain accessible for public, against damages; moreover measurements on this base for verification purposes can be hindered by road traffic and obscurity of visibility.
So, the test base was designed and constructed, with poles located on three sides of polygon in shape of letter Z. In apex points of polygon flat mirrors are firmly fixed; they are appropriately oriented, so to be able to measure precisely sum of polygon sides, equal to 600 meters, by standard distance meter and next by verified distance meter. Owing to such a solution, the whole test base, called Broken Base of Length, is located within area of astronomical-geodetic observatory of the Institute of Geodesy and Cartography, where it can be well protected against damages. As the conducted comparation measurements confirmed, distance meters can be verified on this base with the same accuracy, as in case of straight line bases.

Jerzy Janusz
Some methodical and instrumental solutions for needs of geodetic monitoring of displacements and deformations of curtain walls
During deep excavations, made for constructing multi-storey underground parking lots, different types of walls are used, which shield these excavations from ground sliding and protect the surrounding building against damages. These walls must be controlled during deepening the excavation, due to changeable pressure of the surrounding earth. Displacements of points marked of the wall's surface or points in pipes, which are vertically fixed in walls, are controlled. Author presented the following methodical and instrumental solutions, prepared at the Department of Geodesy IGiK, which facilitate such measurements in usually difficult conditions existing during building works:

• Modular String Inclinometer - instrument for measuring changes of inclination and deflection of wall in vertical profile inside pipe with square profile, stabilised in a wall. Such an inclinometer can be used for determining relative horizontal displacements of points of wall, placed in vertical distances every 1.5 m and for determining deflection of wall on chords, 3 m in length;
• Method and device for centring and stabilising geodetic instruments on vertically fixed pipes with rectangular profile (also on inclinometric pipes);
• Way of determining displacements with the angular type of method of fixed straight line from non-signalled stands.

The presented methods and instruments were verified in the course of measurements on many controlled buildings.

Krystyna Podlacha, Albina Mościcka, Waldemar Rudnicki, Anna Wrochna
Digital Map of Poland at a scale of 1:200 000
Authors discuss in the article problem of creating digital base map, which will enable to quickly acquire cartographic bases with diversified territorial extent and with various degrees of detailness. In Poland there is a problem of creating cartographic base, especially for preparation of thematic maps in regional and country scale, as one can face inhomogeneous cartographic projections, inadequacy of scales of the existing topographic maps, as well as necessity of adding to the cartographic base suitably selected topographic content. In practice costs of creating cartographic base are the major part of total costs related to preparation of thematic maps and usually they are paid every time. Preparation of model of digital base map eliminates this situation and creates conditions for proper functioning of spatial information systems.
The main assumption in preparing Digital Map of Poland was to create universal product, which could be used by a wide range of users, having diversified needs related to detailness of the used base maps, with various cartographic projections and working in different computer systems.
Assumptions, structure, content and possibilities of using Digital Map of Poland are described in the article, as well as examples of its application.

Waldemar Rudnicki
Concept of computer shading of tonal maps -Karkonoski National Park Example
Author discusses in the article method of shading maps, which are prepared on the basis of aerial and satellite photographs. Results of the research works allow for minimising pseudoscopic effect observed on aerial and satellite photographs, which are taken in sunlight on northern hemisphere.
The method is based on using DTM to generate artificial shadows, which have opposite direction in relation to natural shadows produced by sunlight. As a result of applying function of image merging a map of artificial shadows makes correction to the tonal range of photographs. Function, which is applied for correction, retains mid-tones, makes image brighter in lighter parts of shadow map and makes it darker in areas, which have lower density than mean tonal values. This stage enables to eliminate almost totally pseudoscopic effect. The described method does not allow for removing natural shadows, where their contrast is too high.
In order to ensure proper interpretation of aerial and satellite photographs, the added shadows conform to the rules of correct perception of spatial model.
On the basis of the presented method the Landscape Map of Karkonoski National Park has been prepared (compiled from aerial photographs at the scale of 1:30 000, as well as IRS IC and SPOT satellite images). The map was created in two scales: 1:50 000 and 1:75 000. The method was also successfully applied for large-scale maps.

Mieczysław Kołodziejczyk
Quartz gravitational inclinometer
Inclinometers are very important instruments in automatic measuring systems. Hence, quartz inclinometer was designed and constructed at the Institute of Geodesy and Cartography, in collaboration with the Institute of Tele and Radio Engineering.
The inclinometer consists of two pendula and two quartz-crystal resonators. Resonators change their oscillation frequency due to pushing by small balls placed in pendula.
Magnitude of stress is dependent on angle of  inclination of frame, to which the resonators are attached, in relation to pendula.
The presented results of examination of the inclinometer with resonators, having different size: 50 x 6, 5 x 0,5 mm and 50 x 6, 5 x 0,3 mm  revealed, that sensitivity of resonator with 0.5 mm thickness is 6.8 Hz/s, while resonator with 0.3 mm thickness gives precision of measurement 2,95 Hz/s.  On the basis of preliminary examinations of model of quartz inclinometer it was found, that there is a chance to construct precise quartz inclinometer working in differential system. In order to do it, examinations on stability of characteristic in time and thermic studies are needed.

Andrzej Sas-Uhrynowski, Maria Cisak
Absolute gravimetric measurements in Poland
New basic gravimetric network in Poland was established between 1994 and 1999. It is based on 12 points, so-called absolute points; the measurements on these points were done with five ballistic gravimeters: FG 5-101, FG 5-107, JILAg 5, IMGC and ZZG. Absolute points were selected, according to recommendations of the International Gravimetric Commission, on the lowest floors of such buildings, as observatories, museums, schools, churches, etc. It gives a chance, that the absolute point will survive for at least several decades. The paper includes the detailed descriptions of all absolute points. The measurements were performed by German, American, Finnish, Italian and Polish teams. As results of measurements, done with the use of various gravimeters, differed on a few points even by 30 microgals, it was necessary to make their verification. The direct connecting measurements between absolute points were performed with the use of four LaCoste & Romberg gravimeters. The measurements were done on 25 so-called long spans (160–300 km). Results of absolute determinations and results of relative connections were jointly analysed. This analysis enabled to eliminate those gravimeters, which do not fulfil the assumed criteria of reliability – IMGC and ZZG. The remaining gravimeters: FG 5-101, FG 5-107 and JILAg 5, which did not differ in readouts more than 3 microgals, were found to be representatives of the international gravimetric standard. Their readouts were assumed as the standard for Polish gravimetric basic network. The results of relative measurements on 685 spans of network were adjusted to 12 absolute points and to 3 points on the territory of Germany. Finally set of values of gravity acceleration for 354 points of network was obtained. This network is homogeneous, as  far as gravimetric level and gravimetric scale is concerned; it also fulfils accuracy and construction requirements.