Institute of Environmental Physics Im Neuenheimer Feld 229, D-69120 Heidelberg www.iup.uni-heidelberg.de Heidelberg Collaboratory for Image Processing Speyerer Straße 4, D-69115 Heidelberg hci.iwr.uni-heidelberg.de [1] Cox, C. and Munk, W. (1954). Measurements of the Roughness of the Sea Surface from Photographs of the Sun‘s Glitter, J. Opt. Soc. Am. 44(11), pp. 838-850. [2] Kiefhaber, D. (2011). Improved optical instrument for the measurement of water wave statistics in the field, In Komori et al. (eds.): Gas Transfer at Water Surfaces, Kyoto Univ. Press, pp. 358-367 [3] Kiefhaber, D. (2014). Optical measurement of short wind waves – from the laboratory to the field, Dissertation, Universität Heidelberg, Germany [4] Caulliez, G. (2011). Unpublished data from laser slope gauge measurements in the large Marseille Pytheas wind-wave facility, kindly provided by personal communication References:Correspondingauthor: Daniel Kiefhaberdaniel.kiefhaber@iup.uni-heidelberg.deWind wave statistics from specular reflectionsWind wave statistics from specular reflections D. Kiefhaber1), C.J. Zappa2), and B. Jähne1) 1) Institute of Environmental Physics and Heidelberg Collaboratory for Image Processing, Univ. Heidelberg, Germany 2) Lamont-Doherty Earth Observatory, Columbia University, Palisades, NYReflection-based wave measurementsSlope measurementcameras(stereo)FOV:4.2°x3.4°cameraFOV:20°x15°LEDlightsources •brightness of individual reflections is linked to small scale surface curvature •Curvature is very sensitive to changes in environmental conditions •Left: Ship is entering area with surface slick at t = 150 s, curvature decreases, reflection brightness increases •Below: Reflection brightness also has a strong dependence on wind speedCurvature measurement clean rough surface slick smooth surfaceStereo image pair with reflections of the instrument‘s light sources (see right)Heightstereo disparitySlopereflection distributionCurvaturereflection brightnessConclusion and Outlook •New reflection-based instrument capable of measuring slope probability distribution and slick sensitive curvature parameters •Easy to deploy and operate •Robust measurements, day and night •Provides important information on wave field in air-sea interaction experiments •Slope measurement: Like Cox & Munk (CM) sun glitter measurements [1], but with artificial light source! •Area of water surface is illuminated, but reflections are only visible when surface normal points to camera/light source •Surface slope at points of reflection can be computed from position in image uand focal length of lens f: tan α= u/f •Average distribution of reflections = slopeprobabilitydensityfunction! [2]Mean square slope in the field •Fit Gram-Charliermodel to data; similar to CM (left) extract mean square slope σ² •Lab comparison to laser slope gauge [4]: works fine at lower wind speeds •high wind speeds and very limited fetch: Gram-Charliermodel not adequate, leading to an overestimation of mss OSM 2012 / [3]Reflection brightness decreases strongly with wind speed, large variability due to surfactants.Data from Meteor M91, SOLAS-Peru cruise to the upwelling regions off the Peruvian coast. Example reflection images, grayscale inverted for visibility Mean square slope measurements from Peru experiment. Large variability of conditions due to changing presence of surfactants. Data points mostly lie between the CM parameterizations for clean water (solid) and slick (dashed).PDF? •4 week experiment off the coast of Peru •Ship motion correction applied to wave data •Moderate wind speeds, changing presence of surfactants •Changes in surface roughness possible on small spatial scales, < 100 m •Surfactants will likely have big impact on air-sea gas exchange ratesGram-Charliermodel not adequate for high wind speed, very limited fetchvery good agreement for lower wind speedsMeasured 2D slope probability distributionCrosswind profile of 2D slope pdf (along white line)Laboratory validationPDF measu