Pitout, Cedric 
  
This survey has also shown a translation of 29 m (cf. 3.2.1) between an initial plan and the DGPS survey. It is the 
reason why we question the initial map reliability and propose systematic geo-referencing by DGPS. 
Other Road 
Jw S ecundarv Road 
‘Rehabilitated Zone 
‘Contaminated Zone 
Confined Zone 
[33 Building 
ldaste Dump 
  
  
100 — : 200 Métres 
FA, i 
Figure 1. Overlay of a DGPS geo-referencing survey and a geo-referenced and ortho-rectified aerial view(ArcView©) 
4 AERIAL PHOTOGRAPH USE AND INTEREST 
The only accurate way to know the evolution of site occupation is to use time series of aerial photographs. 
4.1 Photographic surveys availability and characteristics 
Until now in France, the National Geographic Institute (IGN) is quite in position of monopoly for the aerial 
photographic survey and management. In general, the regular civil surveys started in the 50's, linked to the development 
of photography and aviation progress. For the Nord-Pas-de-Calais territory, the frequency of photographic surveys is 
33% greater than for the rest of the French territory. This is related to the coal field presence and the intensive past 
industrial activity. 
Except for the nineties, all the available views are in black & white / panchromatic. As the studied sites stopped their 
activities in the end of the seventies, only panchromatic photograph have thus been acquired. The photograph scales are 
between 1 / 30000" and 1 / 4000™. 
4.2 Photograph from paper to numeric 
Scanning is the more adapted method to integrate raster data in a GIS (Star & Dickinson, 1996). After scanning, an 
aerial photograph is composed by an XY array of pixels. The site dimensions are typically inscribed within a square of 
2500 mj, allowing a high scanning resolution (e.g. 1000 dpi for a 1 / 20000* photograph for 1 pixel correspond to 50 
cm). 
  
1158 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.