The data of slope failures is important to make Sabo plan and watershed management. The data is generally acquired by interpreting aerial photographs, but there are several difficulties to acquire accurate data due to the interpreters' ability and transcription error. Remote sensing technology is available to cover them. In consideration of the performance limitation of remote sensing, the auto]detect system for slope failures area has been studied with aerial digital orthophotographs. The system is composed of five processes of (1) gradating the digital orthophotograph into two tones,(2) polygonizing the gradated objects,(3) removing the image noise caused by reflection of broad leaves etc. (4) extracting liner]shaped objects such as river beds and roads and (5) checking these incline. Applying this system to a drainage area produced an adequate result.

Key wordsFauto]detect system, slope failure, digital orthophotograph, remote sensing