fig. 1: MIRA2's adjustable load

A new balancing technique has been developed. It is based on an innovative calibration load, which provides any necessary brightness temperature within the range from cryogenic to ambient temperatures with high precision by mechanical adjustment. In contrast to the well established external beam switching technique, where a second path from the atmosphere with artificial losses is used for reference, a distinctly higher signal to noise ratio of the measured spectral line can be achieved. This considerably improves the measurement of weak lines and extents the usable range of tropospheric conditions. (see Krupa et al. [KRU96b])