Ground-based single-frequency microwave radiometric measurement of water vapour

The integrated water vapour content of the atmosphere is measured by a ground-based radiometer at 22.234 GHz at the Instituto Nacional de Pesquisas Espaciais (INPE), Brazil. The data set has been partitioned into two sets: one for no cloud and the other for cloudy conditions. The attenuation (dB) under the no cloud condition was always found to vary within 1.0–1.5 dB, except at around 1400 hrs (local time) through 1800 hrs (local time), and it reached a value of more than 1.5 dB with a maximum at 1700. This is in conformity with the theoretically calculated values of water vapour density over the same location. An effort has been made to get the regression relation between the measured and calculated water vapour content, for which the RMS error was found to be 0.49 kg m⁻².