Author(s): Ryota Tsubaki; Ichiro Fujita; Kwonkyu Yu; Marian Muste
Linked Author(s): Marian Muste, Ryota Tsubaki, Ichiro FUJITA
Keywords: LSPIV; Smartphone; Ortho-rectification; Floods; Image velocimetry
Abstract: LSPIV (large-scale particle image velocimetry) is an image-based method for measuring velocity distribution on the water surface. Applications of LSPIV have been increasing for both field and laboratory experiments as unique and powerful tools for non-intrusive velocimetry using conventional imaging devices and specialized image processing software. Conventional LSPIV requires explicit ortho-rectification using a set of well-distributed ground control points (GCPs) to connect through geometric transformation image with physical coordinates. The accuracy of the ortho-rectification is a critical factor of the result accuracy. GPSs surveying is, however, a challenging task for large and often difficult to access areas around water bodies in natural environment. This precludes the application of LSPIV in situations where rapid and distributed velocity measurements are needed as it is the case in flood situations. This paper presents an alternative LSPIV configuration using smartphones as imaging device instead of stand-alone video-recorders. In addition to vast processing and communication functions, modern smartphones contain a bundle of sophisticated sensors. By innovatively combining the sensors embedded in smartphones, the images captured with them can be intrinsically and instantly ortho-rectified without making recourse to GCPs. The paper describes the performance of the newly assembled smartphone-based LSPIV system and tests conducted for assessing its accuracy. While a relatively small (for practical purposes) systematic error is observed, the usefulness of the obtained measurements is fully demonstrated. Finally, means to attain future improvements are outlined.
Year: 2015