Dem Measurements of A Gravel-Bed Surface Using Two Scales of Images

Determining the geometry of an exposed gravel-bed surface is important in understanding river flow characteristics. This study presents a method of generating a digital elevation model (DEM) of exposed gravel-bed surfaces using two different scales of images of a riverine environment. The small scale DEM covers an area of 4·5 m × 4·5 m and serves as the reference base, whereas several large scale DEMs provide highly detailed elevation information along the site diagonals. The equipment includes a consumer-grade camera and is light and easy to set up in the field. Highly automated procedures using several off-the-shelf packages ease the burden of generating DEMs of the gravel-bed surface, reducing the technological obstacles for other disciplines. This study evaluates the accuracy of the proposed method at three study sites with different grain sizes along the Hou-Jue River in southern Taiwan. The elevation accuracy obtained by the proposed method was validated by a total station and achieved a root mean square error of 2·9 to 4·3 mm.