Kalibracja dawnych map zasięgu lodów morskich w Arktyce z zastosowaniem systemów informacji geograficznej

Podstawowym materiałem badawczym do analizy zmian w czasie zasięgu lodów morskich w Arktyce są mapy archiwalne. Poprawne przeprowadzenie takich analiz umożliwiają Systemy Informacji Geograficznej (GIS). Celem pracy jest omówienie problemów kalibracji dawnych map lodowych Arktyki z I połowy XX wieku, pochodzących z Duńskiego Instytutu Meteorologicznego. Świadomość błędów, które powstają już w momencie określania pozycji statku czy szacowania odległości do obszarów pokrytych lodem rzuca światło na ogólną dokładność danych, jaka jest niezbędna przy wyborze metod rejestracji.

Archival maps of the region form the base material for the research of changes of the Arctic ice range in time. Correct and accurate analyses are possible thanks to using Geographic Information Systems (GIS). This study is about problems with georeferencing old maps of Arctic ice from the first half of the twentieth century, acquired from the Danish Meteorological Institute (DMI). Awareness of errors in determining the ship’s position or estimating the distance to ice-covered areas sheds light on the overall accuracy of the data, which is essential for the selection of a method of registration – in this case ArcGIS, version 10.0 using the georeferencing toolbar. The reason for using the affine method and problems with map registration have been discussed. The methods of registration taken into account for the purpose of this work have been divided, according to the type of layer to which the scan was knotted, into the following: – Method of point coordinates, – AOI method (linking the area of interest to the corners), – A method of linking the known content of the map (using linear or polygon shapefile). The most precise fit of the coastline has been achieved by using the method of linking the known contents of the map. The use of advanced calibration methods is not always necessary or possible due to the accuracy of the contents of the map. The information which helps recreate the process of creation of old maps and the degree of knowledge of various geographical regions at the time is of special significance. The tools used in the first half of the twentieth century made it possible to determine vessel positions with an accuracy of approximately 15 nautical miles. For calibrating the maps from DMI, the most reliable points to connect will be headlands and any kind of sharp edges of the land, giving the opportunity for clear multiple links in the process of georeferencing (calibration). Using methods based on linking multiple points is not valid if the amount of reliable link points is too small. In the early twentieth century, the only well known areas were the south coast of Greenland, Spitsbergen, Novaya Zemlya, the coast of Norway and Russia. When analyzing old maps of sea ice, we have consider numerous errors resulting from such imperfections as averaging errors, timing errors, location errors, time varying errors of measuring devices used in the first half of the 20th century, and others.