@article {kiefhaber2015a, title = {Influence of natural surfactants on short wind waves in the coastal Peruvian waters}, volume = {12}, year = {2015}, pages = {1291{\textendash}1325}, doi = {10.5194/osd-12-1291-2015}, author = {Daniel Kiefhaber and Christopher J Zappa and Bernd J{\"a}hne} } @article {kiefhaber2015b, title = {Water wave measurement from stereo images of specular reflections}, volume = {26}, year = {2015}, pages = {115401}, abstract = {A new optical instrument for the study of ocean waves, the Reflective Stereo Slope Gauge, has been developed. Its purpose is to measure ocean wave field parameters that are crucial to the air-sea exchange of momentum, heat and gases. The instrument combines a statistical wave slope measurement method similar to Cox and Munk{\textquoteright}s sun glitter technique with a dedicated stereo camera and associated illumination setup for direct wave height measurements. The instrument output was validated under controlled conditions in a wind-wave facility.}, doi = {10.1088/0957-0233/26/11/115401}, author = {Daniel Kiefhaber and Guillemette Caulliez and Christopher J Zappa and Julia Schaper and Bernd J{\"a}hne} } @conference {krall2014a, title = {Air-sea gas exchange under nature-like surfactant influence in the lab}, booktitle = {7th SOPRAN Annual Meeting, Bremen, Germany, 25-26 March 2014}, year = {2014}, doi = {10.5281/zenodo.10900}, author = {Kerstin Ellen Krall and Klaus Schneider-Zapf and Svenja Reith and Daniel Kiefhaber and Bernd J{\"a}hne} } @article {kraeuter2014, title = {High resolution 2-D fluorescence imaging of the mass boundary layer thickness at free water surfaces}, journal = {J. Europ. Opt. Soc. Rap. Public.}, volume = {9}, year = {2014}, pages = {14016}, doi = {10.2971/jeos.2014.14016}, author = {Christine Kr{\"a}uter and Darya Trofimova and Daniel Kiefhaber and Nils Krah and Bernd J{\"a}hne} } @article {kiefhaber2014a, title = {High-speed imaging of short wind waves by shape from refraction}, journal = {J. Europ. Opt. Soc. Rap. Public.}, volume = {9}, year = {2014}, pages = {14015}, doi = {10.2971/jeos.2014.14015}, author = {Daniel Kiefhaber and Svenja Reith and Roland Rocholz and Bernd J{\"a}hne} } @conference {kiefhaber2014b, title = {Measurement of wind waves statistics from specular reflections}, booktitle = {Ocean Science Meeting, 23--28. 02. 2014, Honolulu Hawaii}, year = {2014}, abstract = {The Reflective Stereo Slope Gauge (RSSG) [1] was deployed to two cruises in the tropical Pacific Ocean in Dec. 2011 and Dec. 2012 to measure statistics of small-scale wind waves. During the cruises, both open ocean (Samoa - Hawaii, OSSPRE 2011 on R/V Kilo Moana) and coastal upwelling (off Peru, M91 on German FS Meteor) areas were studied. Surface displacement (wave height time series with 50 Hz sampling rate) was measured by a stereo system with two light sources (Helmholtz stereopsis), while statistics of surface slope were obtained using a method related to Cox \& Munk{\textquoteright}s sun glitter technique [2]. Furthermore, information on the scale of the smallest waves was gained from the brightness of specular reflections (which is related to surface curvature). This parameter is useful for determining the presence of surface slicks. The results underline the importance of monitoring parameters other than wind speed during gas exchange measurements. The presented methods allow for robust estimates of surface slope statistics under a wide range of conditions. [1] Kiefhaber, D., Rocholz, R., Balschbach, G. and J{\"a}hne, B., Improved optical instrument for the measurement of water wave statistics in the field, in: Gas Transfer at Water Surfaces, Kyoto University Press, 2011. [2] Cox, C. and W. Munk (1954), Measurements of the roughness of the sea surface from photographs of the sun{\textquoteright}s glitter, J. Opt. Soc. Amer., 44 (11), 838-850.}, doi = {10.5281/zenodo.12335}, author = {Daniel Kiefhaber and Christopher J. Zappa and Bernd J{\"a}hne} } @phdthesis {kiefhaber2014, title = {Optical Measurement of Short Wind Waves --- from the Laboratory to the Field}, volume = {Dissertation}, year = {2014}, publisher = {Institut f{\"u}r Umweltphysik, Fakult{\"a}t f{\"u}r Physik und Astronomie, Univ.\ Heidelberg}, url = {http://www.ub.uni-heidelberg.de/archiv/16304}, author = {Daniel Kiefhaber} } @conference {kiefhaber2013, title = {Optical measurement of surface ocean waves}, booktitle = {3rd EOS Topical Meeting on Blue Photonics --- Optics in the Sea}, year = {2013}, note = {best student poster award}, doi = {10.5281/zenodo.12334}, author = {Daniel Kiefhaber and Roland Rocholz and Paulus Salomon Bauer and Bernd J{\"a}hne} } @conference {kiefhaber2012, title = {Water Surface Topography Measurements with the Reflective Stereo Slope Gauge}, booktitle = {AGU Ocean Science Meeting 2012, Salt Lake City}, year = {2012}, doi = {10.5281/zenodo.12333}, author = {Daniel Kiefhaber and Julia Schaper and Roland Rocholz and Christopher J. Zappa and William E. Asher and Jessup, A.T. and Bernd J{\"a}hne} } @conference {kiefhaber2011b, title = {Improved optical instrument for the measurement of water wave statistics in the field}, booktitle = {Gas Transfer at Water Surfaces 2010}, year = {2011}, pages = {524--534}, doi = {10.5281/zenodo.14958}, url = {http://hdl.handle.net/2433/156156}, author = {Daniel Kiefhaber and Roland Rocholz and Bernd J{\"a}hne}, editor = {S. Komori and W. R. McGilles and R. Kurose} } @conference {kiefhaber2011a, title = {Mean square slope measurements in the field with the reflective stereo slope gauge}, booktitle = {EGU General Assembly, Vienna}, year = {2011}, abstract = {An optical instrument for the measurement of surface ocean small-scale wave statistics has been developed. This reflective stereo slope gauge (RSSG) is capable of simultaneous measurements of height and slope statistics of the water surface in the field. The instrument is a significant technical improvement of the early work by Waas and J{\"a}hne (1992) and comprises a stereo camera setup, artificial light sources and a wind following system. The measurement principle is similar to Cox \& Munk{\textquoteright}s derivation of slope statistics from photographs of Sun glitter (Cox and Munk, 1954). However, the RSSG uses artificial light sources instead of relying on natural illumination and can thus be used independent of daytime or cloud cover. The probability distribution of the occurrence of specular reflections at given image coordinates can be related to the probability distribution of the surface slope, if the position of the instrument relative to the water surface is known. The slope probability distribution is measured for small slopes up to 0.15. From this partial probability distribution, estimates of the mean square slope (mss) and other statistical parameters can be extracted. The distance from of the instrument to the water surface is obtained from stereo triangulation, while an inclination sensor measures its tilt. Stereo triangulation at the specular reflecting water surface requires the use of two light sources in complementary positions to ensure that both cameras detect reflections coming from the same surface patches. Furthermore, to guarantee that each camera can only sees the corresponding light source, the stereo images are acquired sequentially and the LED light sources are pulsed. The water surface does not change significantly in between the image acquisitions, since the exposure time (and thus the minimum delay of the second image acquisition) is limited to 0.2 ms. The instrument can measure the along-wind and cross-wind mean square slope components, even under varying wind conditions. A wind following system was implemented that is able to rotate the stereo base to keep it aligned in an along-wind or cross-wind direction. Even though the instrument cannot record slope time series and only makes statistic measurements, it has significant advantages over other techniques that are commonly used. Measurements are non-invasive (no instrument parts suspended into or submersed in water) and mostly independent of natural illumination (light source peak wavelength is 940 nm, IR filters suppress skylight, only direct sun glitter may cause complications), not influenced by upwelling light (strong absorption of light at 940 nm by water) and have a spatial resolution that allows the measurement of slope statistics also for capillary waves. At the same time, the (gravity) wave amplitudes can be inferred from the stereo information. The RSSG was characterized and tested in the laboratory and deployed to the Baltic Sea in July and September 2010 to perform local wave statistics measurements at the footprint of heat exchange experiments with the active controlled flux technique (Schimpf et al., 2010). First results from these experiments that demonstrate the capability of the RSSG to measure wave slope statistics in a variety of conditions are presented.}, doi = {10.5281/zenodo.12331}, author = {Daniel Kiefhaber and Roland Rocholz and Julia Schaper and G{\"u}nther Balschbach and Bernd J{\"a}hne} } @conference {kiefhaber2011, title = {Measurement of ocean wave statistics with the reflective stereo slope gauge}, booktitle = {DPG Fr{\"u}hjahrstagung Dresden, Fachverband Umweltphysik}, year = {2011}, abstract = {An optical instrument for the measurement of surface ocean small-scale wave statistics has been developed. This reflective stereo slope gauge (RSSG) is a significant technical improvement of the early work by Waas and J{\"a}hne (1992) and capable of simultaneous measurements of height and slope statistics of the water surface in the field. It comprises a stereo camera setup to measure wave heights by stereo triangulation. The slope measurement is based on Cox \& Munk{\textquoteright}s derivation of slope statistics from photographs of sun glitter (1954) but uses artificial light sources to be independent of natural illumination. The probability distribution of the occurrence of specular reflections in the images can be related to the probability distribution of the surface slope. Although the instrument only makes statistical measurements, it has significant advantages over other common techniques. Measurements are non-invasive (no instrument parts suspended into or submersed in water) and mostly independent of natural illumination (IR light source with}, url = {http://www.dpg-verhandlungen.de/year/2011/conference/dresden/part/up/session/1/contribution/30}, author = {Daniel Kiefhaber and Roland Rocholz and G{\"u}nther Balschbach and Julia Schaper and Bernd J{\"a}hne} } @mastersthesis {kiefhaber2010a, title = {Development of a Reflective Stereo Slope Gauge for the Measurement of Ocean Surface Wave Slope Statistics}, year = {2010}, school = {Institut f{\"u}r Umweltphysik, Fakult{\"a}t f{\"u}r Physik und Astronomie, Univ.\ Heidelberg}, url = {http://www.ub.uni-heidelberg.de/archiv/12673/}, author = {Daniel Kiefhaber} } @conference {kiefhaber2009, title = {Instrument development for combined height/slope/curvature statistics measurements of wind water waves in the field}, booktitle = {Poster abstracts SOLAS Open Science Conference, Barcelona, 16--19 Sep. 2009}, year = {2009}, abstract = {An optical method for the measurement of slope statistics of capillary and short gravity wind waves on the ocean is currently under development. Specular reflections from infrared LED light sources are observed on the water surface with a stereo camera setup. The principle is similar to Cox \& Munk{\textquoteright}s derivation of slope statistics from photographs of the Sun{\textquoteright}s glitter. Fractional area of the speckles in the image is related to the local slope probability distribution, speckle size and brightness is correlated with surface curvature, and the local water height can be inferred from parallax in the stereo images. The instrument measures slope statistics locally, making it a beneficial appendix to air-sea interaction measurements. It is scheduled to accompany heat transfer experiments in the Baltic Sea in phase II of the SOPRAN project.}, author = {Daniel Kiefhaber and Roland Rocholz and Bernd J{\"a}hne} }