High resolution 2-D fluorescence imaging of the mass boundary layer thickness at free water surfaces

Kräuter, Christine; Trofimova, Darya; Kiefhaber, Daniel; Krah, Nils; Jähne, Bernd

doi:10.2971/jeos.2014.14016

Cited by 8 publications

(4 citation statements)

References 23 publications

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“…A very promising technique for fast measurements of gas transfer is the recently developed mass boundary layer imaging technique (Kräuter et al, 2014;Kräuter, 2015). Using this technique will enable the measurement of the gas transfer velocity simultaneously and in the same footprint as the heat transfer velocity.…”

Section: Discussionmentioning

confidence: 99%

Measurements of air–sea gas transfer velocities in the Baltic Sea

2019

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Abstract. Heat transfer velocities measured during three different campaigns in the Baltic Sea using the active controlled flux technique (ACFT) with wind speeds ranging from 5.3 to 14.8 m s−1 are presented. Careful scaling of the heat transfer velocities to gas transfer velocities using Schmidt number exponents measured in a laboratory study allows us to compare the measured transfer velocities to existing gas transfer velocity parameterizations, which use wind speed as the controlling parameter. The measured data and other field data clearly show that some gas transfer velocities are much lower than those based on the empirical wind speed parameterizations. This indicates that the dependencies of the transfer velocity on the fetch, i. e., the history of the wind and the age of the wind-wave field, and the effects of surface-active material need to be taken into account.

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Section: Discussionmentioning

confidence: 99%

Measurements of air–sea gas transfer velocities in the Baltic Sea

2019

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“…At the same footprint on the water surface, we can also visualize the horizontal structure of the mass boundary layer, allowing us to investigate interactions between waves, near-surface turbulence and gas exchange [27].…”

Section: Discussionmentioning

confidence: 99%

High-speed imaging of short wind waves by shape from refraction

Kiefhaber

Reith

Rocholz

et al. 2014

J. Eur. Opt. Soc.-Rapid Publ.

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This paper introduces the first high-speed system for slope imaging of wind-induced short water waves. The imaging slope gauge method is used, which is based on the shape from refraction principle. The downward looking camera with a telecentric lens observes the refraction of light rays coming from a high power custom telecentric LED light source that is placed underneath the wind wave facility. The light source can be programmed to arbitrary intensity gradients in the x-and y-direction, so that the origin of a light ray is coded in intensity. Four gradient images (acquired at 6000 fps) are combined for one 2D slope image. By only using intensity ratios, the measurements become independent of lens effects from the curved water surface and inhomogeneities in the light source. Independence of wave height is guaranteed by using telecentric illumination and telecentric imaging. The system is capable to measure the slopes of a wind-driven water surface in the Heidelberg Aeolotron wind-wave facility on a footprint of 200 × 160 mm with a spatial resolution of 0.22 mm and a temporal resolution of more than 1500 fps. For the first time, it is now possible to investigate the structure of short wind-induced waves with sufficient spatial and temporal resolution to study their dynamic characteristics without aliasing effects. Example images and a video of a 3D reconstructed water surface are shown to illustrate the principle.

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“…In this way it is for example possible to derive surface drift velocities [5]. If the gas exchange process is also made visible and detectable for cameras by a fluorescent dye and suitable light sources, then thermography together with cameras that operate in the visible wavelength regime, can be used to get a visual comparison of gas and heat exchange processes at the air-water interface [6,7].…”

Section: Introductionmentioning

confidence: 99%

Active thermography as a tool to investigate heat and gas transfer across the airwater interface

Kunz

Jähne

2016

Proceedings of the 2016 International Conference on Quantitative InfraRed Thermography

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Gas and heat exchange between the ocean and the atmosphere are a key process in the earth system. Active thermography is a tool that can be used to estimate heat and gas transfer rates with unprecedented temporal and spatial resolution compared to other measurement techniques. In this paper recent technical progress of this method is described: a) a spatially more homogeneous heating of the water by a carbon dioxide laser for measurements with a significant lower systematic error and statistical uncertainty, and b) a new modulation scheme for faster measurements. While the latter is essential for field measurements, the first enables the distinction of different models for air-water gas exchange in the laboratory.

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High resolution 2-D fluorescence imaging of the mass boundary layer thickness at free water surfaces

Cited by 8 publications

References 23 publications

Measurements of air–sea gas transfer velocities in the Baltic Sea

Measurements of air–sea gas transfer velocities in the Baltic Sea

High-speed imaging of short wind waves by shape from refraction

Active thermography as a tool to investigate heat and gas transfer across the airwater interface

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