water90 + water92 = water 
vegetation90 + vegetation92 = vegetation 
water90 + vegetation92 =vegetation 
vegetation90 + water92 =vegetation 
Preliminary conclusions. Such a plan contains the 
floating reed islet position during the two recording 
years. Measuring the distance between two positions on 
that plan, we could establish its average shifting speed 
(about 3 m per day). As its shifting direction is not a 
linear one owing to the predominant wind directions and 
lake bed configuration, this rough value could be seen as 
minimum. 
(B) For the statistical study of the natural patrimony 
changes from the last 1981 updating, a new so-called 
NOUPLAN plan has been compiled using the linkage 
between the plan from which the dynamic phenomena 
were removed (L90SAU92) and the 1981 digitised plan 
(PLAN81). This time, no commutative rules were used to 
point out changes but only supplementary attributes. 
Rule3: L900R92 * PLAN81 =NOUPLAN 
LAC * LAC LAC, 
VEGET + VEGET = VEGET, 
LAC + VEGET = LAC, 
VEGET + LAC = VEGET,, 
  
Preliminary conclusions. m index shows a change, but 
n index shows an unchangeable result. Adding surfaces 
with the same index, the change situations are quickly 
established. The analysis points out the water surface 
variation during the two reference years (1990 and 1992) 
- is about 100 ha against 2,200 has water we have 
investigated (i.e. a 5 per cent variation). The variation 
based on the oldest investigate plan PLANSI, is 450 has 
as against 2,200 has (i.e. a 20 per cent variation). These 
variations are caused by the permanent setting up and 
destruction of the floating reed islets owing to the wind 
and water action. 
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International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B4. Vienna 1996