Non-intrusive underwater measurement of mobile bottom surface

This paper reports a novel approach for underwater measurement of mobile bottom surface by using an inexpensive 3-D depth sensor - Kinect. The sensor is tested in controlled conditions for surface profiling of rigid objects of different colors placed under varying water depths, turbidity, illuminosity and sensor height. Measurements indicate random errors are present when the object is in air only and these errors can be eliminated by smoothing. However, systematic errors were observed in the presence of water and are attributed to refraction. A refractive correction equation is developed to remove those systematic errors. Validation of the sensor's performance, quantification of its limitations and a systematic procedure for its use in underwater profiling is presented. Finally, capabilities of the sensor as an underwater measurement device for laboratory applications are demonstrated by measuring erosion of cross-stream sand bar due to overtopping and evolution of mining-pit.