DETERMINATION OF CHANGES IN PHENOLOGICAL CYCLE 
OF OAK-WOOD BY MULTISPECTRAL NOAA/AVHRR IMAGES 
Mladen Viher, Remote Sensing Laboratory, Croatia 
viher@zvonimir.morh.tel.hr 
M.Sc. Visnja Vucetió, Meteorological and Hydrological Service of Croatia 
vucetic@cirus.dhz.hr 
ISPRS Commission VII, Working Group 4 
KEY WORDS: PHENOLOGICAL PHASE, AVHRR, NDVI, DYNAMIC CLUSTERING 
ABSTRACT 
Using NOAA/AVHRR satellite images during one year period and monitoring changes of Normalized Difference 
Vegetation Index (NDVI) and variations in multispectral feature space, occurrences of phenological phases for the oak- 
woods (Quercus robur) in five lowland locations in the Republic of Croatia was noticed. Average annual variation of NDVI 
was computed along with criteria for detection of the most distinct phenological phases. Changes in the multispectral 
feature space were noticed and using of dynamic clustering was suggested for determination of time-dependent features. 
This method could be used for monitoring oak-woods, which are not included in agrometeorological network in Croatia 
and even in neighbouring countries. 
1. Ground data 
Phenology is the science, which studies the 
regularity of  periodical appearances in plant 
development from the beginning to the end of the 
vegetation period. Regular phenological observations 
comprise the recording of the phenological data such 
as the beginning of springing, leafing, blooming and 
ripening of special cultures, fruit-trees, forest trees and 
any other plants. These observations have been 
performed in the agrometeorological stations. 
In this paper three phenological stations: 
Bjelovar, Kutina and Zupanja, which are the nearest to 
observed oak-woods, have been analysed. Four 
development stages for the oak-trees are observed 
(commencement of leafing and blooming, appearance 
of acom and yellowing of leaves). The dates of these 
phenophases during 1992 are presented in the table 1. 
It is shown that the dates of individual development 
stages are same or similar for all three stations except 
for Bjelovar for the yellowing of leaves. 
Quercus robur is second of the most spread 
wood types in lowlands of Croatia (only beech is widely 
spread). Huge woods between Sava and Drava rivers 
(See fig. 1) are the most preservative woods in the 
Central Europe. In the middle part of Sava valley alone, 
lowlands oak-woods covers, in broken continuity, over 
900 km”. Lonjsko polie (Lonja field) belongs to this area 
in which three of chosen oak-woods are located (llovski 
dol, Opeke and Srnolov). Cesma oak-wood lies north of 
them and it is a protected park of nature too. Wood 
basen with the largest area in lowlands of Croatia is 
Spatva covering around 400 km?. 
Table 1 The dates of oak-trees phenophases for Bjelovar, Kutina and Zupanja during 1992. 
  
  
  
  
  
  
  
  
  
  
Stations First leafing First blooming Appearance of Yellowing of 
Bjelovar 16 April 22 April 17 September 6 November 
Kutina 18 April 23 April 17 September 26 October 
Zupanja 14 April 23 April 16 September 26 October 
  
  
750 International Archives of Photogrammetry and Remote Sensing. Vol. XXXII, Part 7, Budapest, 1998 
  
  
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