LANDSAT-MISS画像からエッジとして検出できる五葉山周辺地域の尾根線及び谷線の条件

抄録

This paper investigates the conditions for ridge lines and valley lines to be detected as edges in the LANDSAT-MSS imagery with respect to their directions, their side slope angles, the sun azimuth and evelation. The test site is specified around Mt. Goyo in Iwate Prefecture, Japan which has a typical ups and downs topography. First, by using the LANDSAT data of three seasons and 159 standard samples of ridge lines and valley lines, the detection rates by five kinds of edge detection operators were evaluated. The results via the average-difference operator (AV-DIF) applied to the band-7 images demonstrated the highest marks. Then by introducing a model of illuminated side slopes by the sunlight, an index of BD is defined as the difference of cosy values of the side slopes where γ means the angle between the normal vector of a slope and the vector to the sun. The critical values for the ridge lines to be detected by AV-DIF from the band-7 images were found to be around 0.3. The same approach was also applied to the pure cosy images, which were synthesized from the digital elevation model and the sun position at the image collection. Then almost equal results to these of the real imageries were observed. As BD depends on the sun position, the detection efficiency for each sample varies temporally. In the test area, the BD values of the ridge lines and the valley lines of which directions are near to the southeast stay in low levels for all seasons even though they have rather steep side slopes.