Water vapor excess path-length (WVEP) in atmosphere, in spite of its much smaller average value than a dry air component which is stable, makes larger seasonal and diurnal variations. An estimation algorithm for WVEP is improved for less errors even in large opacity of the atmosphere and the multi-algorithm program (MAP), together with the Wu-algorithm of JPL in CalTech, is applied to make the least estimation error. A limitation of the MAP is also discussed. The differential emission measurement (DEM) is also applied to WVEP estimation is order to reduce additional errors due to measurement errors of antenna temperature, which can make them a half through one tenth of those by another algorithms. The experimental results gave proof of the effectiveness of the DEM.

Attenuation measurements of clear atmosphere were made for eight months by observing sky brightness temperature with a dual-frequency microwave radiometer in no use of extraterrestrial radio sources. High resolution measurements or data processing were realized by a differential emission measurement (DEM) method which could largely reduce an additional attenuation error due to measurement error of brightness temperature to about one tenth in comparison with a conventional emission measurement method. A simple approximate equation of atmospheric attenuation was derived as a function of brightness temperature. True brightness temperature can be retrieved from the approximate equation and the DEM method even if measured brightness temperatures include much constant errors.

Measurements of a far-field gain of a large Cassegrain antenna with shaped reflectors by defocusing method are discussed. Defocused-path-length variation of a shaped antenna does not considerably differ from that a conventional Cassegrain antenna. In a model antenna, even when the maximum spherical phase error is 180 degrees, defocusing method can give the far-field gain within 0.1 dB error, if the illumination does not change by defocusing.