A New Method for Determining the Emissivity of the Human Skin in Vivo

To determine the radiation emmitted by the human skin, the emissivity of its surface must be known. In this work is presented a new procedure to measure the emissivity of the human skin in vivo. The proposed method is based in the calculation of the difference of two images: one acquired before projecting a laser beam on the surface of the skin, and the other alter such projection. The resulting "difference image" contains only the reflected radiation, which is used to calculate the emissivity of the skin making use of the Kirchhoff\´s law and the Helmoholtz reciprocity relation. With this method non-contact measurements are made, and the temperature of the skin is not required. Additionally, with the proposed method it is possible to determine the emissivity of the skin at specific wavelengths. The method is presented using a CO₂ laser whose wavelength is in the range of maximum radiation of heat by the human skin.