Water at the ice point: a useful quasi-blackbody infrared calibration source

Water at the ice point makes a good calibration source in the 4- to 13-microm spectral region because of its high emissivity, small skin depth, and the ease with which an ice-point bath may be prepared and used. In a simple ice bath the emissivity is slightly less than unity, and we have calculated corrections that allow one to predict the apparent radiation temperature of the equivalent blackbody. We propose an alternate configuration that uses an auxiliary mirror. This configuration should provide an emissivity extremely close to unity.