@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}
}
@techreport {gbalsch2004,
	title = {HD-WHOI Measurements October 2004 CISG},
	year = {2004},
	institution = {Institute for Environmental Physics, University of Heidelberg},
	author = {G{\"u}nther Balschbach}
}
@incollection {jaehne2002f,
	title = {Wellenbewegte Wasseroberfl{\"a}che},
	year = {2002},
	pages = {259--262},
	publisher = {Wichmann},
	url = {http://d-nb.info/96618503X},
	author = {Bernd J{\"a}hne and G{\"u}nther Balschbach and D. Fu{\ss}},
	editor = {Thomas Luhmann}
}
@phdthesis {balschbach2000,
	title = {Untersuchungen statistischer und geometrischer Eigenschaften von Windwellen und ihrer Wechselwirkung mit der wasserseitigen Grenzschicht},
	year = {2000},
	publisher = {Institut f{\"u}r Umweltphysik, Fakult{\"a}t f{\"u}r Physik und Astronomie, Univ.\ Heidelberg},
	abstract = {Using color image processing a refraction based technique for retrieving the slope of a water surface covered with waves has been substantially improved. This multichannel technique is similar to photometric stereo analysis for opaque surfaces. The three independend channels of a color camera allow simultaneous detection of both surface gradient components. The third information is used for normalization to the total illumination intensity for every individual pixel, leading to an increased linearity and enhanced robustness. Errors due to inhomogeneous illumination or disturbance by small particles in the water can be corrected almost completely. For combined measurements the technique can be reduced to two colors. Measuring only one slope component normalization is still possible. At two wind/wave facilities statistical and geometrical information for small scale waves were obtained and compared to results from authors using other techniques. Two combined experiments were conducted. At different scales the wave field and the underlying flow field were observed simultaneously. Hering [1996] computed kinetic energy density and vorticity of the flow field in a 10cm x 10cm frame. In the second combined experiment M{\"u}nsterer [1996] measured concentration profiles of a tracer gas in a 4cm x 4cm section in the viscous boundery layer. Both experiments provided new insights in the interaction between capillary waves, turbulence in the flow field and in the boundary layer respectively.},
	url = {http://www.ub.uni-heidelberg.de/archiv/2473/},
	author = {G{\"u}nther Balschbach}
}
@conference {jaehne1999r,
	title = {The Heidelberg Aelotron --- a new facility for laboratory investigations of small-scale air-sea interaction},
	booktitle = {The Wind-Driven Air-Sea Interface: Electromagnetic and Acoustic Sensing, Wave Dynamics and Turbulent Fluxes},
	year = {1999},
	note = {Poster},
	doi = {10.5281/zenodo.14857},
	author = {Bernd J{\"a}hne and Horst Hau{\ss}ecker and Uwe Schimpf and G{\"u}nther Balschbach},
	editor = {M. L. Banner}
}
@conference {jaehne1999m,
	title = {The Heidelberg Aeolotron - a new facility for laboratory investigations of small scale air-sea interaction},
	booktitle = {Poster presented at: The Wind-Driven Air-Sea Interface: Electromagnetic and Acoustic Sensing, Wave Dynamics and Turbulent Fluxes},
	year = {1999},
	abstract = {The study of small-scale air sea interaction still lacks suitable facilities. No facilities are available with large fetches and correspondingly high wave ages. Furthermore almost no large facility is suitable for measurements with sea water, is clean enough for controllable experiments with surface films or sufficiently gas tight for gas exchange measurements. Currently a new large annular wind/wave facility with quasi unlimited fetch is under construction at the Institute for Environmental Physics of Heidelberg University. An annular facility is not a new idea. A 40 m diameter facility ({\textquoteleft}{\textquoteleft}storm basin{\textquoteright}{\textquoteright}) was already built shortly after World War II in Sevastopol for wind/wave interaction studies. Various small circular facilities for air-sea gas exchange studies have been used since the late seventies at Heidelberg University and later at Woods Hole Oceanographic Institution for air-sea gas exchange studies. The new facility builds on the experience with these facilities but now reaches a critical size. It has an outer diameter of 10 m, the channel is 0.65 m wide and 2.4 m high and can be filled with water up to a height of 1.2 m. It is thus a rather deep facility. Only the wind/wave flume of the Hydraulic facility at Scripps Institution of Oceanography is deeper with a depth of 1.5 m. Since the maximum phase speed of the waves is 3.4 m/s, high wave age conditions can be reached at least for low and medium wind speeds. The facility is designed for a maximum wind speed of 15 m/s. Water currents can be generated separately by a set of thrusters. The air space is gas tight and the materials that come into contact with the water and air make experiments possible with de-ionized water, artificial seawater, surfactants, and reactive gases. Water temperatures and heat fluxes across the interface range from 5o to 35oC and from -0.5 to 1 kW/m2, respectively. We plan to focus in the next decade on measurements revealing the mechanism of air-sea gas transfer including the effects of surfactants and waves. The new facility will be open for guest scientists. The experimental possibilities of the facility are detailed to show the opportunities for international cooperation.},
	author = {Bernd J{\"a}hne and Horst Hau{\ss}ecker and Uwe Schimpf and G{\"u}nther Balschbach}
}
@conference {balschbach1998,
	title = {Multichannel shape from shading techniques for moving specular surfaces},
	booktitle = {ECCV 1998},
	volume = {1407},
	year = {1998},
	pages = {170--184},
	publisher = {Springer, Berlin},
	organization = {Springer, Berlin},
	doi = {10.1007/BFb0054740},
	author = {G{\"u}nther Balschbach and J. Klinke and Bernd J{\"a}hne},
	editor = {Burkhardt, H. and Neumann, B.}
}
@conference {balschbach1997,
	title = {Multichannel shape from shading techniques for reconstruction of specular surfaces},
	booktitle = {Tagungsband Herbsttagung des Graduiertenkollegs "3D Bildanalyse und -synthese"},
	year = {1997},
	publisher = {H.-P. Seidel, B. Girod, H. Niemann (Hrsg.)},
	organization = {H.-P. Seidel, B. Girod, H. Niemann (Hrsg.)},
	author = {G{\"u}nther Balschbach and J. Klinke and Bernd J{\"a}hne}
}
@conference {hering1996a,
	title = {A novel system for the combined measurement of wave- and flow-fields beneath wind induced water waves},
	booktitle = {Proc. 18th Int. Congr. for Photogrammetry and Remote Sensing},
	volume = {31},
	number = {B5},
	year = {1996},
	pages = {231--236},
	doi = {10.5281/zenodo.14894},
	url = {http://www.isprs.org/proceedings/XXXI/congress/part5/},
	author = {Frank Hering and G{\"u}nther Balschbach and Bernd J{\"a}hne and P. Waldh{\"a}usl},
	editor = {K. Kraus}
}
@conference {jaehne1996a,
	title = {The role of active vision in exploring growth, transport, and exchange processes},
	booktitle = {Aktives Sehen in technischen und biologischen Systemen, Workshop der GI-Fachgruppe 1.0.4. Bildverstehen Hamburg, 3--4. December 1996},
	volume = {4},
	year = {1996},
	pages = {194--202},
	publisher = {infix},
	organization = {infix},
	author = {Bernd J{\"a}hne and Horst Hau{\ss}ecker and Frank Hering and G{\"u}nther Balschbach and J. Klinke and Martin Lell and Dominik Schmund and Michael Schultz and Ulrich Schurr and Mark Stitt and Ulrich Platt},
	editor = {B Mertsching}
}
@conference {hering1995c,
	title = {Flow- and wave-fields associated with micro-scale wave breaking as measured simultaneously by particle tracking and wave slope visualization},
	booktitle = {IAPSO Proceedings, XXI General Assembly, Honolulu, Hawai, August 1995, PS-10 Spatial Structure of Short Ocean Waves},
	number = {19},
	year = {1995},
	pages = {385},
	abstract = {Longuet-Higgins predicted the development of a capillary roller at the crest of a short gravity wave, being the consequence of the existence of parasitic capillaries, (Capillary rollers and bores, J. Fluid Mech, Jan. 1992). According to the theory any free surface, at which the tangential stress vanishes, a surface vorticity is produced. The mean vorticity at the edge of the Stokes layer is of the order of 2(ak) f, ak being the slope and f the radian frequency of the wave. Hence capillary waves, with a high value of a are accompanied by particular large vorticity feeding the vortex roler at the crest of a short gravity wave. This phenomenon has been investigated at the circular facility of the Institute for Environmental Physics. At the same location, simultaneous time series of wave slope images and the Lagrangian flow field were obtained using an integrated optical set-up, including particle-tracking and wave-slope instruments. The particle tracking measurement yields drift- and bulk-velocities, Reynold stresses and the vorticity distribution beneath the wave, while the imaging wave slope gauges gives the 2D-slope and the height of the waves. First results from the measurement campaign of early 1995 will be presented.},
	author = {Frank Hering and G{\"u}nther Balschbach and M. Menzel and Dietmar Wierzimok and Bernd J{\"a}hne}
}
@conference {balschbach1995,
	title = {A new instrument to measure steep wind-waves},
	booktitle = {IAPSO Proceedings, XXI General Assembly, Honolulu, Hawai, August 1995, PS-10 Spatial Structure of Short Ocean Waves},
	number = {19},
	year = {1995},
	pages = {387},
	abstract = {Current instruments to measure the spatial structure of short waves are limited to quite low slopes. Capillary waves, however, may show slopes well above one (45 degrees inclination). A new instrument has been designed to measure the spatial structure of steep capillary waves. It was designed to specifically address a number of basic questions: Is the limiting form for Crapper capillary waves ever reached? Can a bubble be trapped by such a wave? Do solitary capillary/gravity waves - as recently postulated by Longuet-Higgins - exist in wind/wave fields? The instrument uses the basic design as used in previous instruments of our research group but includes two important enhancements. By the use of a telecentric illumination and camera lens, the influence of wave height on the slope measurement is eliminated. Colored light is used to encode both slope components simultaneously and to correct for uneven intensity distribution in the light source and intensity losses by reflection at the water surface. This contribution describes the setup of the instrument and its calibration in detail. First results from the circular wind/wave facility at Heidelberg University are reported in a separate paper.},
	author = {G{\"u}nther Balschbach and M. Menzel and Bernd J{\"a}hne}
}
@mastersthesis {balschbach1994,
	title = {Verschiedene Verfahren zur Visualisierung und Gr{\"o}{\ss}enbestimmung von Gasblasen in Wasser},
	year = {1994},
	school = {Institut f{\"u}r Umweltphysik, Fakult{\"a}t f{\"u}r Physik und Astronomie, Univ.\ Heidelberg},
	doi = {10.5281/zenodo.14562},
	author = {G{\"u}nther Balschbach}
}
