Premium
An optical tachometer for short‐path measurement of flow speeds in shallow overland flows: improved alternative to dye timing
Author(s) -
Dunkerley David L.
Publication year - 2003
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.468
Subject(s) - tachometer , path (computing) , computer science , flow (mathematics) , environmental science , simulation , acoustics , remote sensing , geology , telecommunications , physics , mechanics , detector , programming language
Tracers, such as uorescein dye, are widely employed to measure overland ow speeds by time‐of‐travel along measured ow paths. Among several disadvantages of this method are the involvement of human reaction time when using stop‐watches, and the relatively long travel path that is consequently needed for reliable timing. Long ow paths mean that local variability along the ow path cannot be detected. This paper describes a new optical tachometer that overcomes these limitations, as well as offering other advantages. It is based on the use of a small oating reector target that is carried on the surface tension lm, and which passes between two reective sensors mounted above the ow. The new device allows virtual ‘spot’ measurements of surface ow speed over a path as short as 1 cm, and eliminates the inuence of human reaction time. The new device is battery powered and portable, and provides an improved alternative to dye timing in many eld and laboratory applications. Its use will allow the collection of more rened data than have hitherto been easily achievable. Copyright © 2003 John Wiley & Sons, Ltd.