Ruprecht-Karls-Universität Heidelberg Heidelberg Graduate School of Mathematical and Computational Methods for the Science Graduiertenkolleg 1114 Heidelberg Collaboratory for Image Processing Institute of Environmental Physics Novel Technique for 3D-Space Visualization of Concentration Fields of Air-Water Gas Transfer Darya Trofimova, Christine Kräuter und Bernd Jähne Heidelberg Collaboratory for Image Processing, Institute of Environmental Physics, University of Heidelberg, Germany Measuring Technique NH4+ NH3 Z C Water Phase Air Phase H+ NH4+ Z C H+ NH3 NH3 OH- ﬂuorescence z* z* znl NH3(aq) + H3O+ <-> NH4 ++H2O 1D Measurements: Experimental Set-up wind Basler acA2500 - 14gm Basler acA2500 - 14gm diode laser beam expander laser beam ﬂuorescent light from Pyranine air-sided camera water-sided camera glass window of the facility Wind-wave facility: Lenght = 1.75 m Width = 25 cm Depth = 20 cm Water volume ≈ 22 L Air volume ≈ 220 L Optical Set-up: ·Diode laser: wavelength - 445 nm ·Galileo expander ·Basler cameras: 2592×16 AOI 2.2×2.2 µm pixel size 350Hz frame rate ·Scheimpﬂug optics magniﬁcation: 0.43 air-side 0.32 water-side Fig.2. Sketch of the LIF experimental set-up for 1D measurements 1D Measurements: Results Fig.5. Experimental proﬁles for diﬀerent ammonia concentration with ﬁtted functions that comply with small-eddy model Fig.4. Experimental proﬁles for diﬀerent Pyranine concentration 3D Measurements: Experimental Set-up sCOM pco.edge sCOM pco.edge sCOM pco.edge 1.4 m 1.0 m LED ﬂuorescent water surface left camera middle camera right camera 3D Measurements: Results Conclusion: free stream velocity 1.8 m/s, friction velocity in water 3.7 cm/s free stream velocity 2.2 m/s, friction velocity in water 5.5 cm/s free stream velocity 2.6 m/s, friction velocity in water 6.4 cm/s Fig.3. Time-depth images of the temporal ﬂuctuations of ammonia in the water. The size of the vertical coordinte is 9.25 mm and horizontal coordinate - 13.75 sec. ammonia ﬂux ammonia ﬂux Fig.1. Sketch of NH3 invasion into the acid water for low and high concentrations of NH3. The main objective of modiﬁed LIF technique is to gain simpliﬁed shape of concentration ﬁelds of observed molecules. This can be achived by demanding the vertical concentra- tion proﬁles to have a steep decay at the certain depth resulting in binary ﬁelds. Fig.6. Sketch of the LIF experi- mental set-up for 3D measurements Fig.7. Example of estimated disparity maps. Lower disparity values correspond to higher distances. The images are 0.6s apart. The wave breaking event is visible. Large Annual Aeolotron Facility: Height = 2.41 m Width = 60 cm Water volume ≈ 18000 L Air volume ≈ 25000 L Optical Set-up: ·blue high power LEDs (wavelength - 455 nm) ·sCMOS cameras pco.edge 2160×2560 resolution 6.5×6.5 µm pixel size 100Hz frame rate Full Camera Calibration: estimation of intrinsic and extrinsic parameters for each camera Dense Reconstruction: every image was rectiﬁed to compute the disparity map using images from left and right camera. Block matching algorithm is used to ﬁnd correspondence between the images. - The experimental technique for mass boundary layer visualization was veriﬁed with the measurements of concentration proﬁles at the linear wind-wave facility with high spatial and temporal resolution. - The binary representation of concentration ﬁelds can be achieved with Pyranine concen- tration of 10-5 mol/L and initial pH value of 4. Varying ammonia concentrations in the air, the fraction of mass boundary layer can be investigated. - The technique allows observation of binary concentration ﬁelds at larger spatial scales. The invasion of ammonia was viewed with multiple camera set-up from underneath the fa- cility. The third dimension was reconstructed using stereo algorithm, beneﬁting the picture of a gas exchange through the air-water interface in four dimensions. NH4+ NH3 OH OH 7th International Symposium on Gas Transfer at Water Surfaces doi: 10.5281/zenodo.17672 7th Internati