the image is georeferentiated. The “image georefentiation" process consists in: 
• identifying on the images the Ground Control Points (GCP's); these pixels or “ reference points", of known 
geographic coordinates, reproduces some characteristic ground features easily identifiable, 
• handling the original image by means of specialized software to project its pixels onto a new’ plane, conform to 
a selected map projection system, and assigning map coordinates to them. Here the GCP’s. enough for the kind 
of the adopted transformation, are forced to take the the known cooordinate positions, while the other pixels 
are rearranged extrapolating their positions. 
3. THE ANTARCTIC GCP’s ACQUISITION PROCEDURE 
A comprehensive library of GCP’s will be produced in order to georeferentiate satellite images to cover the 
whole area involved in the PNRA research activities. Presently, unluckily, only a small area around the Italian base 
(at Terra Nova Bay) is covered: during three of the past expeditions a certain number of GCP's has been collected 
and a well defined procedure for their acquisition has been developed with the purpose of having proper, correct 
and uniform information for each point. The GCP’s acquisition procedure is composed of two phases: 
• the first takes place in Italy and concerns the selection of the areas on satellite images where GCP's can be 
found satisfying the need of the uniform distribution despite the wide white zones (snow or ice); a defined 
priority is assigned to these areas (“1” is the maximum”) and again to several smaller zones for each different 
area selected (“a” is the maximum) - see Fig. 1-a; 
• the second one takes place in Antarctica where the operator reaches, via helicopter, the selected areas (and 
zones) - see Fig. 1-b - and measures, by a Global Positioning System equipment, the three coordinates (latitude, 
longitude, height) of a GCP according, if possible, to the priorities indicated - see Fig. 1-c. 
The procedure has its practical limits on two aspects: 
• only an aerial approach to the selected area permits the proper recognition of the site where a GCP can be 
found, 
• the operator can make mistakes in the recognition of the site: a snow storm, a season time different from that of 
the satellite image acquisition.and so on, may produce some similar ground features in the same selected area. 
Moreover, technical problems rise in the GCP’s acquisition, each one linked to the other. They are listed below: 
• only a low number of satellites are visible over the horizon at each time. 
• all the visible satellites have very low azimuth angles of viewing. 
• the rate of the ionispheric noise is very high. 
• only double-band differential GPS stations permit the needed accuracy (few meters) in the acquisition 
procedure and the distance (tens to hundreds kilometers) between the wanted GCP’s, 
• the acquisition time range is very wide (1 hour or more) for the required accuracy. 
The GCP’s would be visible on images taken at different weather conditions and times: consequently a high rate of 
GCP’s has to be collected for each different area. The library, presently, has been converted in a thematic layer, to 
be used in an antarctic G.I.S. and each GCP is correlated to a small image sourronding the point. 
4. ORTHORECTIFICATION OF ANTARCTIC IMAGERY 
To produce orthoimages of antarctic areas, two different software products have been used: Ortho-Module 
and OrthoMAX, both delivered by ERDAS Inc. In order to obtain good results from the processing both the 
softwares recommend the uniform distribution of the GCP’s over the image, a reasonable degree of contrast within 
the images and their radiometric similarity: this is not true for the Antarctica. We have, therefore, tested the 
performances of the two softwares in extreme parameters characteristics conditions. The imagery used in both the 
works is a stereoscopic pair of SPOT level 1A (raw sensor data - only radiometric correction have been applied)