River Surface Water Topography Mapping at Sub-Millimeter Resolution and Precision With Close Range Photogrammetry: Laboratory Scale Application

Abstract

High precision and high density measurements of surface water topography in laboratory rivers are useful in hydro-morphodynamic studies to analyze energy, momentum, and mass balances in the river system. A close range photogrammetry (CRP) method is developed to provide instantaneous sub-mm vertical and horizontal resolutions of surface water topography along a flowing laboratory river reach, which is infeasible with typical mechanical and point-based river stage measurements. The CRP method uses wax powder seeding of the river surface and two synchronized nonmetric digital cameras to capture stereo-pair images and derive digital elevation models (DEMs) of the river surface water topography. The river water surface DEM accuracy was limited by extent and density of wax coverage, control point accuracy, lighting conditions, as well as camera and lens specifications. Two Nikon D5100 16.2 MP CMOS digital SLR cameras with 20 mm prime lenses were mounted 1.3 m above the river water surface, generating DEM horizontal resolution of 0.3 mm. Control point elevation was surveyed using ultrasonic sensors with 0.3 mm vertical accuracy. The sub-mm overall DEM accuracy was based on ultrasonic sensor measurements at check points and overall DEM precision was based on differences between repeated images. We demonstrate how the CRP method can generate river surface water topography and bathymetry in a laboratory meandering river and suggest methods for successfully applying CRP in natural river surface water topography mapping.