Electromagnetic Wave Surface Velocimetry

Electromagnetic wave surface velocimeters (ESVs) measure the Doppler shift in electromagnetic waves reflected from the water surface. They provide nonintrusive water surface velocity measurements from bridges and river banks. Comparisons with laboratory and field tests show very good agreement over a wide range of elevation and planview angles. Laboratory testing shows comparable results between ESV and other measurement techniques when 0.4<V<1.6m∕s and 15<θ<45° . Field testing at three different locations shows that the optimal operation conditions are at an elevation angle θ≈30° , planview angle φ<13° , and 0.30<V<2.00m∕s . The ratio of cross-section-averaged velocity to mean free surface velocity is approximately CFDAV≈0.88 for high flow velocities during floods. The standard deviation of the field measurement for these three streams was less than 15% of the mean value.