デジタル航空写真を用いた渡良瀬遊水地における植生高の推定

抄録

Information on the ground surface can now be acquired easily and with high accuracy by using digital aerial photographs. A digital canopy model (DCM), which is calculated by subtracting a digital terrain model (DTM) from a digital surface model (DSM) of the vegetation, provides useful information for studies of wild animal habitats and plant species distributions. However, DCMs have been used mainly for forests, and their validity for herbaceous plants requires further verification. In this study, we used the ADS40 airborne digital sensor to clarify the relationship between a DCM and the height of herbaceous species. Our study area was the Watarase wetland in the northern Kanto Plain, central Japan. Suitable habitat conditions for the many rare plants found in this wetland are maintained by controlled burning in early spring. We acquired three DSMs: just after the controlled burn in April 2006; in August 2006, when the vegetation height was maximal; and in April 2007, also just after the controlled burn. We calculated the DCM from the difference between the August DSM and a DTM developed by using the minimum height values from the two April DSMs. We also performed a field survey at the time of the August DSM acquisition, during which we measured the height of the uppermost leaves with a measuring pole at 16 measurement points and estimated the vegetation structure from photosynthetic photon flux density (PPFD) profiles measured with quantum sensors at each point. The calculated DCM height was highly correlated with the height of the uppermost leaves (r² = 0.96), but was about 100 cm lower. In contrast, the DCM and the height of maximum intercepted PPFD were highly correlated (r² = 0.97) and showed a 1:1 relationship.