Abstract
The definite investigation method of the debris volume derived from the bare mountainside has not been established. Around the Ashio desolate mountainous area, photogrammetric comparative measurement of surface height of some model zones settled on mountainside is carried out through the large airphotographs taken at intervals of about one year by helicopter. Mean deviation value of height of each model zones is applied to all mountainside classified to each type beforehand by photointerpreta-tion to tctalize the produced volume of debris. Though the measurement error is estimated as about ±3.6cm, this method is considered to be effective for this purpose at nowaday.
