Effeciency and Limitation of Interpretations of Ponds (Blanken) from Aerial Photographs : based in a sample area of the Tateyama-Midagahara Lava Plateau

Abstract

The writers tried to distinguish the ponds (Blanken) (most of them are 2-3 meters in diameter) on the Midagahara lava plateau from aerial photographs (color positive films on a scale of I to 15,000 published by the Geographical Survey Institute and a black-and-white positive film on a scale of I to 20,000 published by the Forestry Agency) with special reference to their image processing. The results are shown below. (1) In three small investigation areas settled on grass land on the Midagahara lava plateau, most of the ponds could be distinguished on the monitor pictures by raising the magnification of the camera unit to the size of 70-120 and adjusting the slice level of the apparatus. In this case, most of the ponds were shown as group O (darkest tone =black color) on the monitor pictures. The smallest ponds found by this method were about 1 meter in their minor axis. On the other hand, about the distinction of the vegetation around the ponds, it could be interpreted on that particular occasion that the difference of light intensity among the vegetation groups was clear like, for example, the difference found between Narthecium asiaticum Maxim. and its surrounding vegetation groups in autumu. (2) Then the writers tried to distinguish the ponds in the extended large investigation areas by the same method. As a result, about 900/0 of the black indications found to be the same as group O on the monitor pictures, proved to be real ponds and the remaining 100/0 were trees, bare rocks or others. However, the latters could be mostly distinguished from the ponds by means of their scales and characteristic features. In addition, we could not find any big difference between color and black-and-white positive films as to the interpretation of the ponds and the vegetations by this method.