Water wave measurement from stereo images of specular reflections

Kiefhaber, Daniel; Caulliez, Guillemette; Zappa, Christopher J.; Schaper, Julia; Jähne, Bernd

doi:10.1088/0957-0233/26/11/115401

Cited by 5 publications

(5 citation statements)

References 41 publications

(27 reference statements)

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“…Full ness parameter χ which is proportional to the mean square slope can be estimated (Kiefhaber et al, 2015). During M91, the instruments were installed at the bow of R/V Meteor (see Fig.…”

Section: Back Closementioning

confidence: 99%

“…Only in conditions when sun glint is visible in the RSSG images can the data not be processed. The RSSG measures the probability for slope zero, its inverse, the surface roughness parameter χ is proportional to mss (Kiefhaber et al, 2015). The proportionality constant is calibrated against the night-time measurements of the probability density functions (see Appendix B).…”

Section: Measurements During M91mentioning

confidence: 99%

“…Full ability distributions were measured under controlled conditions. From an earlier experiment, measurements of the mean square slope with a Laser slope gauge (LSG) were available (Kiefhaber et al, 2015). This reference data set is used to validate the mean square slope extraction by fitting a model function to the measured probability distribution.…”

Section: Back Closementioning

confidence: 99%

“…The Reflective Stereo Slope Gauge (RSSG) measures a surface roughness parameter (χ ) which is proportional to the mss and derived from the probability for zero slope (Kiefhaber et al, 2015). Unlike the wave probability distribution measurements, the RSSG is not impacted by daylight, unless there is sun glint in the image.…”

Section: Appendix B: Rssg Mss Calibrationmentioning

confidence: 99%

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Influence of natural surfactants on short wind waves in the coastal Peruvian waters

Kiefhaber

Zappa

Jähne

2015

Preprint

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Abstract. Results from measurements of wave slope statistics during the R/V Meteor M91 cruise in the coastal upwelling regions off the coast of Peru are reported. Wave slope probability distributions were measured with an instrument based on the reflection of light at the water surface and a method very similar to the Cox and Munk (1954b) sun glitter technique. During the cruise, the mean square slope (mss) of the waves was found to be very variable, despite the limited range of encountered wind speeds. The Cox and Munk (1954b) parameterization for clean water is found to overestimate mss, but most measurements fall in the range spanned by their clean water and slick parameterizations. The observed variability of mss is attributed to the wave damping effect of surface films, generated by increased biological production in the upwelling zones. The small footprint and high temporal resolution of the measurement allows for tracking abrupt changes in conditions caused by the often patchy structure of the surface films.

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Section: Back Closementioning

confidence: 99%

Section: Measurements During M91mentioning

confidence: 99%

Section: Back Closementioning

confidence: 99%

Section: Appendix B: Rssg Mss Calibrationmentioning

confidence: 99%

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Influence of natural surfactants on short wind waves in the coastal Peruvian waters

Kiefhaber

Zappa

Jähne

2015

Preprint

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“…Methods have been developed based on specular reflection of an image projected on the water surface. 13,25 Kiefhaber et al 25 used specular reflection to their advantage in a novel stereo imaging approach where two cameras were mounted within infrared light-emitting diode (LED) arrays and focused on the same region. Their system uses an inverted light path with two cameras and two ultraviolet (UV) LED arrays, where each camera is mounted in an LED array.…”

Section: Introductionmentioning

confidence: 99%

Application of photogrammetry for spatial free surface elevation and velocity measurement in wave flumes

Fleming

Winship

Macfarlane

2018

Proceedings of the IMechE

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This article presents a method for obtaining the spatial free surface elevation and velocity field for the water surface in a wave flume over a relatively large measurement area for this type of application (approximately 1.5 m × 1.5 m). The technique employs proprietary videogrammetry software to post-process stereo images captured by multiple synchronised machine vision cameras. Dimensional resolution and other limitations are similar to that experienced for particle imaging velocimetry systems ( x, y resolution of 2 mm). Imaging of the free surface was enabled by the use of millions of bespoke slightly positively buoyant fluorescent flakes. Ultraviolet light was used as the primary light source to excite the fluorescent flakes. Reflected ultraviolet light was attenuated by a high-pass filter fitted to the cameras so that only the emitted light from the fluorescent flakes was visible. The software was validated using a simple linear translation experiment. An application is demonstrated for the radiated wave field generated from a submerged sinusoidal heaving sphere for two cases: one single and five consecutive oscillations. Results agree with linear wave theory which indicates that the floating flakes had minimal impact on the water surface particle motion at the scale tested. It is, therefore, concluded that spatial measurement of the free surface elevation and velocity using the method presented has good resolution over a large measurement field. The flakes were found to follow the free surface well, but the measurement area is constrained to where the pattern of flakes exists in the image. Hence, application of floating markers is not suitable for experiments with significant outflow/upwelling which would wash away the floating markers from the intended measurement area.

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