Abstract
In order to diagnose physiological activities of individual trees growing in urban area, a remote sensing using a thermographic system from a helicopter was examined at the temple of“Heirin-ji”and adjascent area in Saitama Prefecture. Under cloudy and steady-state thermal conditions the information about activities of physiological functions such as stomatal movement, transpiration, photosynthesis, and air pollutant absorption was obtained from the thermal image of trees. The slight injury, which was found in the field survey of individual trees, was diagnosed by the thermal image, although it was not detected from aerial photographs in color. The difference in species of trees was also detected by the thermal image.
The stomatal conductance of several tree species measured by a porometer, which is an indicator of stomatal opening, decreased with a lowering of PPFD. The decrease rate was large at PPFD below 200μmol photons m-2 sec-1 but it was small and constant at PPFD above 300μmol photons m-2 sec-1. This result means that it is possible to diagnose stably the slight injury of trees from the thermal image measured under a cloudy sky with PPFD above 300μmol photons m-2 sec-1.
The resolution and error in temperature image measured by the thermographic system depended on spatial distributions of temperature. When the difference (5°C) between high and low temperatures in the image was given by slits with zigzag patterns, the resolution and error were ca. 300 lines and ca. 5% (0.25°C) at 50 slits. This result shows that it is necessary to measure at a height below 300 to 500 m in order to obtain the exact temperature of individual trees within 5% in error.
