空中写真を使った沖積平野の乾湿区分法

抄録

In Japan, the surface moisture condition of a cultivated field has conventionally been divided into three ranks: dry, semi-dry and wet. These ranks correspond to depths of the water table, as determined by digging a pit or by hand augering, of more than 70 cm, 70 cm to 30 cm, and less than 30 cm respectively.
In this study, however, we attempted to determine surface moisture by photo interpretation using panchromatic photographs taken in before the riceplanting, in May 1973 Yokote Basin, in Akita prefecture.
Landforms of the alluvial plain, defined according to their constituent materials which to a large extent, control the surface moisture condition. Surface moisture condition at each landform unit was closely related to the average photographic density.
In this study, the moisture condition of the cultivated field was divided into four ranks: (1) dry, (2) semi-wet, (3) wet and (4) extremely wet, based on the result of geomorphologic classification and tone grade.
According to the check hand-drilling in the field, the results were recognized to have a 70 % accuracy. Moreover, in most cases where there was a discrepancy, both the photointerpretation rating and the actual soil condition were wetter than the rating based on water table depth. Consequently, classification of ground water level by the photointerpretation is judged to be sufficient accurate for practical use.