Figure Z. 5chematic overview o1 tne proposeu tiens 
(Further analysis) 
  
    
bad » 5 
Figure 3a NOAA-AVHRR image (bandl, 27 April 199 
   
3) with aggregated parent material 
  
    
LS 
  
polygons as overlay. The area is located in 
south-western Germany and north-eastern France; the central light-coloured area is the Rhine valley. 
environmental impact of agriculture in that region is 
determined; both procedures do not exist so far. Besides the 
spatial units to which the method is applied need to be 
optimised. 
The spatial objects currently used are administrative units. 
Those are not related to the physical environment which puts 
constraints on agriculture. As a result environmental 
disturbance may provoke different responses within one unit, 
complicating the interpretation of observed changes. Alternative 
units show a homogenous reaction to disturbance from 
agriculture and are thus physically defined. Polygons resulting 
from aggregation of the European soil map (CEC, 1985) 
according to parent material are proposed. Parent material 
strongly determines agricultural potential. For a test area in 
Western Europe they show a much higher coincidence with land 
cover units as observed in a NOAA-AVHRR image than 
administrative units (figure 3a and 3b). To enable monitoring at 
national level the parent material polygons are intersected with 
national borders. 
To these polygons the change detection procedure will be 
applied every 5 to 10 years, depending on the monitoring 
frequency. The basic assumption of the procedure is that 
changes in environmental impact are caused by changes in land 
use, which cause changes in land cover as well. By comparing 
the old and new land variograms of remote sensing images, 
changed regions are identified. The images are available shortly 
after recording providing almost real-time information. 
To make check whether the observed changes are caused by 
agriculture a land cover classification is performed in the 
regions concerned. All regions where the (changed) area 
exceeds a certain threshold are entered in the change 
identification procedure. 
The basic assumptions of the change identification procedure 
are that higher agricultural intensity results in increased 
environmental impact and in higher yields. An indicator is 
developed relating actual yield to the range from limited to 
potential yields. This yield indicator is used to quantify the 
general environmental impact. Comparison to the old indicator 
value reveals whether the situation improved or degraded. It 
does not reveal information on specific problems like 
eutrophication or erosion, for which further research is needed. 
The potential and limited yield can be calculated at the end of 
the growing season when the actual weather data are available. 
Actual yield figures are often not readily available on short term 
and will thus delay the final outcome of the method. This can be 
improved by faster publication of yield figures or by deriving 
them from remote sensing. In the latter case they would be 
available shortly after the growing season as well and the 
method would provide real-time information on environmental 
impact by agriculture. 
4. CONCLUSION 
The proposed method is expected to provide quick insight in 
regions where the environmental impact from agriculture 
changed. It is less time-consuming than the currently used agri- 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 67