@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}
}
@article {zappa2004,
	title = {Microbreaking and the enhancement of air-water transfer velocity},
	journal = {J. Geophys. Res.},
	volume = {109},
	year = {2004},
	pages = {C08S16},
	abstract = {The role of microscale wave breaking in controlling the air-water transfer of heat and gas is investigated in a laboratory wind-wave tank. The local heat transfer velocity, k_H , is measured using an active infrared technique and the tank-averaged gas transfer velocity, k_G , is measured using conservative mass balances. Simultaneous, colocated infrared and wave slope imagery show that wave-related areas of thermal boundary layer disruption and renewal are the turbulent wakes of microscale breaking waves, or microbreakers. The fractional area coverage of microbreakers, A _B , is found to be 0.1-0.4 in the wind speed range 4.2-9.3 m s-1 for cleaned and surfactant-influenced surfaces, and k_H and k_G are correlated with A _B . The correlation of k_H with A_B is independent of fetch and the presence of surfactants, while that for k_G with A_B depends on surfactants. Additionally, A_B is correlated with the mean square wave slope, <S 2>, which has shown promise as a correlate for k_G in previous studies. The ratio of k_H measured inside and outside the microbreaker wakes is 3.4, demonstrating that at these wind speeds, up to 75\% of the transfer is the direct result of microbreaking. These results provide quantitative evidence that microbreaking is the dominant mechanism contributing to air-water heat and gas transfer at low to moderate wind speeds.},
	doi = {10.1029/2003JC001897},
	author = {Christopher J. Zappa and William E. Asher and Jessup, A. T. and J. Klinke and S. R. Long}
}
