Geoinformation Issues Vol. 10, No 1, 2018
Geoinformation Issues Vol. 10, No 1, 2018
Edotorial pages, contents, reviewers of journal to download
Walyeldeen Godah, Andenet A. Gedamu, Tulu B. Bedada
On the contribution of dedicated gravity satellite missions to the modelling of the Earth gravity field – A case study of Ethiopia and Uganda in East Africa
Abstract: Since the first decade of this millennium, the three dedicated gravity satellite missions (DGSMs): CHAMP (Challenging Minisatellite Payload), GRACE (Gravity Recovery and Climate Experiment) and GOCE (Gravity field and steady-state Ocean Circulation Explorer) had remarkably contributed to the modelling of the Earth’s gravity field and its temporal variations. Moreover, in 22 May 2018, the GRACE-FO (GRACE Follow-On) has been launched to continue the measurements of GRACE satellite mission. On the basis of data from those DGSMs, Global Geopotential Models (GGMs) are continuously developed. The main aim of this research is to evaluate the recent GGMs and assess the contribution of DGSMs to the modelling of the Earth’s gravity field over East Africa. Gravity functionals, e.g. quasigeoid height and gravity disturbance, obtained from recent GGMs developed with the use of data from DGSMs were evaluated using terrestrial gravity data available in Ethiopia and GNSS/levelling data in Uganda. The results obtained were analysed and discussed. The main findings reveal an improvement of ca. 40–50% on the modelled gravity field from GGMs that include data from GOCE satellite mission.
Elzbieta Welker, Anna Jedrzejewska
A study of changes in the Earth's magnetic field in Poland in the years 1954-2017; reducing the archival values of magnetic declination at the points of the magnetic network to a uniform epoch
Abstract: At the turn of the 1980s and 1990s, the Institute of Geodesy and Cartography developed a method of reducing magnetic declination based on 40-year long magnetic observations at repeat stations. This method assumed that changes in the magnetic field at repeat stations can be described using the polynomial of the 3rd degree as a function of the position of the point (φ, λ) and the measurement epoch. The Earth’s magnetic field as a temporal-spatial physical phenomenon of a variable, unpredictable nature is, however, difficult to model in a longer period of time.
At the turn of the centuries the magnetic declination values at the points of the magnetic network were reduced to the 2000.5 epoch using the polynomial function for field modelling, based on the analysis of the actual changes in magnetic declination at repeat stations and in magnetic observatories. The unified set of points of the magnetic network with declination reduced to the 2000.5 epoch constituted the base for further studies of geomagnetic field.
In the last dozen or so years, the network of the magnetic points has been updated by the new measurements of magnetic declination at over 300 points. Not all previous locations were suitable for re-measurements. In this case, a point in the nearby region that met the conditions for magnetic measurements was selected. New points, with the values of magnetic declination reduced to the measurement epoch, updated and expanded the data bank. An analysis of the course of actual changes in the Earth’s magnetic field in the observatories of Central Europe and at the repeat stations of the national magnetic control of Poland from the measurement epoch, i.e. from the 1950s to the current epoch, made it possible to unify the set with points with the magnetic declination determined. From now all the points will have the value of declination assigned to the 2017.5 epoch. Thus, the procedure for the reduction of magnetic data to subsequent epochs will be simplified. The decision about the possible re-updating of the data will be taken after analysing the course of further changes in the Earth’s magnetic field in Central Europe from the 2017.5 epoch.
Radoslaw Gurdak, Patryk Grzybowski
Feasibility study of vegetation indices derived from Sentinel-2 and PlanetScope satellite images for validating the LAI biophysical parameter to monitoring development stages of winter wheat
Abstract: The main objective of the presented work is to assess applicability of vegetation indices derived from non-commercial and commercial satellites for monitoring development stages of winter wheat. Two types of data were used in the study: Sentinel-2 and PlanetScope images. Various vegetation indices were derived from these data and correlated with ground measured LAI values. The results of the study revealed that there is a good relationship between satellite based indices – Normalized Difference Vegetation Index – NDVI, Enhanced Vegetation Index – EVI, Soil Adjusted Vegetation Index – SAVI and ground based LAI, but strength of this relation depends on the phase of crop development. Sentinel-2 and PlanetScope data are suitable for estimating LAI with high accuracy and their precision for LAI determination is very similar. Depending on availability, they can be used interchangeably. The highest correlation between ground measured LAI and vegetation indices for Sentinel-2 appeared SAVI – r = 0.862 (phase: early tillering) and for PlanetScope NDVI – r = 0.667 (phase: ripening). Compatibility of average LAI values derived from PlanetScope and Sentinel-2 images are 33.21% and 10.63%.
Patryk Grzybowski, Radoslaw Gurdak
Changes in the built-up areas at the aeration wedges of City of Warsaw
Abstract: The main objective of this paper is to present increasing share of built-up areas at the aeration wedges of City of Warsaw. The idea of Warsaw aeration corridors had been arisen in 1916 and was adapted to the present times in 1992, 2006 and 2018 in the planning’s documents which described Warsaw spatial development conditions. The goal for creation these corridors has been to establish the air exchange between areas around the city (especially green areas) and downtown. The analyses were carried out for years: 1992, 1995, 1998, 2001, 2004, 2006, 2009 – based on Landsat-5; 2013 – based on Landsat-8; 2015, 2018 based on Sentinel-2. As a result of research, it was found that aeration wedges had been constantly built-up. In 1992 built-up areas covered 14% (767 ha) of aeration corridors, in 1998 – 17% (918 ha), in 2006 – 24% (1245 ha), in 2013 – 26% (1341 ha), in 2018 – 27% (1383 ha). The largest loss of green areas was noticed as: arable lands and meadows – from 42% to 29%. In addition, during the research it was observed that new buildings have been situated in unfavorable way. New buildings are the walls and barriers to the air masses coming to the downtown.
Michal Kaluski, Agata Hoscilo, Radoslaw Gurdak
Accuracy assessment of the Copernicus Buildings Height 2012 layer based on the city of Warsaw
Abstract: The techniques of converting stereo-pair aerial photographs or satellite images are used to prepare the digital surface models (DSM), digital elevation models (DEM) or to obtain the height of the objects. Recently, the Copernicus Land Monitoring service released a product presenting the building heights for the major – capital cities in Europe. The Building Height 2012 layer was derived based on the stereo images acquired by the IRS-5 satellite close to the defined reference year 2012. The main aim of the study was to examine the accuracy of the Copernicus Building Height 2012 layer in comparison with the building height derived from airborne laser scanning system. The study was carried out over the city of Warsaw (the capital of Poland). In general, data from both datasets are compatible, however the overestimation of the height was observed.
The comparison carried out in two ways produced similar results. On average, the overestimation of the satellite-based building height for the study area reached 1.08 m.
Joanna Tuszynska, Martyna Gatkowska, Karolina Wrobel, Katarzyna Jagiello
A pilot study on determining approximate date of crop harvest on the basis of Sentinel-2 satellite imagery
Abstract: The paper presents a pilot study which was designed to determine whether Sentinel-2 satellite data can be applied for assessing the approximate date of crop harvest. The in-situ data collection is demonstrated, and further analysis of spectral reflectance of crops in selected spectral bands, in the period before and after harvest, is presented. The relation between the reflectance of Shortwave Infrared (SWIR) spectral bands and the crops status was found. The results are discussed and the need for further studies is indicated.