The Noise Project in the Electromagnetics Division of the National Institute of Standards and Technology (NIST) has proposed the development of standards for microwave brightness temperature for use in remote-sensing applications such as satellite-based weather observations. The standards would be based on existing fundamental standards for electromagnetic noise in waveguide systems. The connection to brightness temperature, which is a radiated quantity, would be made by means of a well characterized antenna. A heated calibration target would be used to supplement the basic standard, either as a check or to reduce the uncertainty by a redundant measurement. We have performed preliminary measurements at 26 GHz that demonstrate the feasibility of the proposed standard. A parallel effort is in progress for terahertz frequencies. For terahertz noise we are building a heated target to be used as a noise standard, since we did not already have fundamental noise standards for such high frequencies. This standard will be used with a terahertz radiometer. The radiometer is based on a receiver that uses a hot-electron bolometer (HEB) mixer that is coupled to the radiation by a quasi-optical adapter. We expect to perform terahertz noise measurements with the system by the end of the year.

We report on the design of a radiometer for traceable noise-temperature measurements at terahertz frequencies, including noise measurements on cryogenic IF components, development and test of quasi-optical adapter technology, development of black body standards, and overall system design.