11. Bioengineering and Bio-thermal Fluid Dynamics

Gaseous water vapor in the atmosphere affects physiological and chemical processes, and its concentration, humidity, is an important factor in various fields including living environment design, hygiene control, and high-precision processing technology. Water vapor concentration is measured by a hygrometer or a dew point meter. They are based on a system in which the change of the electrical or optical characteristics of the sensor caused by water adsorption is used for humidity calculation. Although these sensors can perform local monitoring at a fixed point, a detailed evaluation of the spatial distribution or the flow of vapor is difficult. In this study, the water vapor in the atmosphere was visualized utilizing the near-infrared (NIR) absorption band of water molecules. Imaging by the optical absorption of the target molecules did not require any probe. The laser beam of the wavelength of 1870 nm, included in one of the absorption bands of water, was made incoherent and collimated to irradiate to the observation area. The transmitted light was captured by an NIR camera equipped with a telecentric lens. Since the light absorption of dilute water vapor caused only a slight decrease in the intensity in the image, the absorbance difference was calculated as the logarithm of the ratio between the intensity of without and with the vapor to emphasize the change. Also, baseline correction and filtering were carried out to remove noise derived from flickering and speckles in the optical system. The color map of the resulting absorbance difference successfully provided the visualization of the flow of moist air in an open atmosphere. The vapor emission from various sources was then visualized by the presented system.

Prof.

Naoto Kakuta

Corresponding author