Sun as a broadband source for tropospheric attenuation measurements at millimetre wavelengths

The Sun can be used as a broadband extraterrestrial source of centimetre- and millimetre-wavelength radiation for long-term monitoring of tropospheric attenuation along ground-to-space paths. In interpreting these data, it is, however, necessary to take into account the variations in intensity of the source and also its changing position in the sky. Possible effects on the attenuation statistics due to the continuously changing position of the Sun, both diurnally and annually, are considered. Provided that care is taken in the interpretation of the data, the Sun provides a useful, and considerably cheaper, alternative to satellite-borne sources, and it is capable of yielding much of the information that can be obtained from the latter, with the exception of phase data. It has the additional advantage of being usable over a very wide frequency range.