Abstract: An apparatus and method for temperature and concentration measurement at liquid surfaces using reflectance. The apparatus includes a light source which produces a measurement light beam, and also includes a detector. The measurement light beam has a measurement light beam intensity and impinges on the surface of the liquid specimen. It reflects back as a reflected light beam with a reflected light beam intensity which is related to the reflectivity R of the liquid surface and to the measurement light beam intensity. The detector receives the reflected light beam and determines the reflected light beam intensity. Either the temperature or concentration of the liquid specimen can then be determined based on the reflected light beam intensity. The light source can be a coherent light source, such as a laser. A beam splitter can be provided to split the light beam from the light source into a reference light beam and the measurement light beam.