In field conditions, direct measurement of plant interception is still a difficult task, especially because of methodological limitations and also that of technical and organizational nature. [Olszewski, 1984, Kossowska-Cezak et al., 2000].The way to deepen the knowledge about the determinants of interception in forest areas is research in controlled conditions [Anzhini et al,. 2007], which could provide the data for the identification of the mathematical models. Pei et al.  performed a laboratory simulation of precipitation on a set tree surface by changing the intensity of the rain ten times in the range of 47.4 to 147.6 mm/h. Similarly, Keim et al.  applied a rate of 20 to 420 mm/h by changing the droplet size of the simulated precipitation from 1.0 to 2.8 mm. These amounts of precipitation are not likely to occur in the Polish climate.
The essence of the research was to spray trees with simulated rain with certain characteristics, according to the methodology previously developed and tested on mockups.To carry out the research on trees interception of simulated rain in the range of 2 to 11 mm/h autors had to design and build a sprinkler device [Klamerus - Iwan et al., 2013] taking into account the difficulty with getting low intensities. The aim of this paper are methods of modification and testing of that device. The adopted general research assumptions, as well as the developed original technique for measuring trees interception in the laboratory conditions can be assessed positively. That is because the obtained measurement results can be logically interpreted, and can prove useful for identifying mathematical models built on sound science.
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