Wavenumber-frequency analysis of river surface texture to improve accuracy of image-based velocimetry

¹ Graduate School of Engineering, Kobe University, 657-8501 1-1 Rokkodai, Nada, Kobe, Japan
² Department of Civil Engineering, Kobe University, 657-8501 1-1 Rokkodai, Nada, Kobe, Japan

^* Corresponding author: kojiro0531@gmail.com

Abstract

In the unseeded image-based techniques for river surface flow measurements, advection speed of surface textures composed of surface ripples or floating objects is measured by image analysis. However, the methods would yield erroneous information when the surface texture is affected by gravity waves propagating in all directions. In order to improve the measurement accuracy, such wave effects have to be subtracted in the image analysis. For that purpose, a wavenumber-frequency analysis was applied to a space-time image (STI) generated in the space-time image velocimetry (STIV) analysis and succeeded in eliminating the wavegenerated pattern contained in the texture in STI. It was made clear that turbulence-generated texture propagates at the speed of surface flow.