Surface image velocity measurement system for wide rivers using smartphones

Kwonkyu Yu, Byungman Yoon, Seokmin Lee

Thursday 2 july 2015

16:30 - 16:45h at Africa (level 0)

Themes: (T) Special session, (ST) Acoustic monitoring of flow, turbulence and river discharge

Parallel session: 13F. Special session: Acoustic monitoring of flow, turbulence and river discharge

The objective of the present study is to develop a real-time surface image velocity measurement system for wide rivers using several smartphones. Each smartphone works as an independent measuring unit, e.g. an image current meter. Since the camera of a smartphone has a limited viewing angle, one smartphone can only measure a limited width of the river at a time. To measure the entire width of a wide river, several smartphones are linked together. Each phone takes images of a portion of the river and analyzes the surface velocities from the images taken. Then the analyzed velocity data is transferred to a tablet PC which acts as a server computer. In the server, the velocity of the river width is reconstructed as a whole. Each smartphone runs on an Android operating system. It also measures its location and angles (pitch and roll) using its built-in sensors and calculates the distance to the measurement area on the water surface. The only parameter to that needs to be entered in is the height of the phone from the water surface. After being set up, the camera of the phone starts to take images. For the normal NTSC type video camera, it captures 30 frames per second. With the help of OpenCV library, we split the frames of the video and analyzed the images to work out the water surface velocity field. The image processing algorithm was based on a correlation analysis of spatio-temporal images, similar to the traditional STIV (Spatio-Temporal Image Velocimetry). Since all the image processing is performed in the smartphone itself, the SIV system can measure the water surface velocity literally in real-time. The preliminary test showed that the developed system was highly effective and convenient. The measured results showed that the system was useful for river flow measurement work.