Angle Effects of LIDAR Measurements on a Flat Surface and in High-Velocity Spillway Flows

Measurements in aerated high-velocity spillway flows have been traditionally conducted with point-source instruments. LIDAR is a promising remote sensing technology that may be able to provide more detailed insights into the free-surface properties. So far only one laboratory study has investigated the use of LIDAR technology in air-water flows on a spillway model showing that free-surface data in the aerated part of the flow can be recorded with high spatial and temporal resolution. However, the spillway model, as well as the aerated flow region, were quite short and further research is needed to test the performance of LIDAR technology on a longer spillway. Herein, the present study tested a LIDAR in an 8.6 m long laboratory spillway with strip roughness. To ensure consistency of results along the spillway, the performance of the LIDAR was first assessed without flowing water along a straight wall as well as in the spillway model without water. The results showed that the LIDAR was affected by viewing angle that can be corrected using a scaling factor. The LIDAR was subsequently used to measure the free-surface properties of skimming flows. Comparative results for three different LIDAR measurement positions showed effects on the free-surface elevations and standard deviations linked with the different grazing angle of the LIDAR relative to the free-surface and with the waviness of the free-surface. A potential correction scheme for this is discussed