Fatehi, Ahmad 
  
Therefore, the image of 1990 (non-polluted year) with the 1991 image (polluted year) were used to investigate the 
relation between NDVI and distance. Two pathways were selected. The first one was along the gradient of height 
and distance from the source of the pollution, the second one was along the coast. Figure 4 shows the relation 
between NDVI values and distance (first one), from near the source of the pollution to the mountains. 
Relation between NDVI and distance from the source of the pollution in 1990 & 1991 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
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| * NDM180 & NEM 1991 Linear (NDM 1900) — Linear (NOM 1991) 
  
Figure 4: Relationship between NDVI values and distance to the source of the pollution in 1990 and 1991. Direction 
of the sampling path is eastward starting from the coast of the Persian Gulf and ending in the Zagros Mountains 
range. As the graph shows the gradient of the best fit line is steeper in 1991 because the NDVI values near the 
source of the pollution decreased very much while far from the Persian Gulf in the mountain area these differences 
are reduced. 
7 Image differencing for investigation of AVHRR (GAC) NDVI changes 
Changes in NDVI between 1990 and 1991 were studied. For this purpose the average NDVI images of the growing 
seasons of these years were produced, then the difference of those average NDVI images was calculated. The NDVI 
Difference map (NDVI91-NDVI90) shows a maximum change of NDVI values close to the Persian Gulf north of 
Busheher, Ahwaz, Dezfool and Ilam. Figure 5 show sliced map that produced from NDVI1991-NDVI1990, 
  
430 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.