In this study, we developed a unique topographic measuring method for landform in a small area where outlook is not good. The method was applied to an uninvestigated keyhole-shaped tumulus covered with woody vegetation in a study area of Itoshima City. We also examined the technique for creating DEM indicating realistic landform.
At the beginning of the measuring, multiple control points were installed in the study area. Each one is installed where other two ones can be seen. We measured two horizontal distances from two of them to a target point and a vertical distance from eitherit to the target one by using two simple laser rangefinders. The measuring was carried out in cooperation with two persons holding the laser rangefinders and one person standing a staff on the target one.
The coordinates of the target one can be calculated using these measured values by trigonometric functions, three-square theorem and addition in Excel. Finally, we introduced a concept of traverse surveying in the calculation for the coordinates, reduced coordinate error and increased the measuring reliability. We applied the measuring method including the calculation process on the control points to all measuring points.
Kriging in GIS is appropriate as a method to create DEM from the obtained coordinate data of the control points and the measuring ones. In a relief map and a contour map made from the DEM, we could measure the length, width, height and direction of the tumulus accurately and identify small scale landforms of it such as the stepped structure, remains of grave robbing and traces of landslides.
Three characteristics of the measuring method can be mentioned. The first one is to measure the landform by using only two simple laser rangefinders. The second one is to reduce blind spots in the measuring by changing the reference control points according to the situation. The third one is that obtained DEM has better accuracy than existing large scale map information.
Consequently, the topographic measuring method is considered to be a simple, inexpensive and useful for landform in a small area where outlook is not good.

View full abstract