Some measurements of attenuation by rainfall at 18.5 GHz

We discuss 18.5 GHz attenuation measurements on a 6.4 km path within the Holmdel rain gauge network. The period of measurement includes the summer of 1967 during which many very heavy showers occurred. We examine the data for individual storms separately. There is a marked variability. For example, one shower shows strong evidence of an updraft. The composite results show that
$\gama = 0.041 \Sigma_{i}d_{i}R_{i}^{1.04}$
where γ is the attenuation per unit length, R
i
is the rainfall rate in millimeters per hour measured at the ith rain gauge on the path, and d
i
is the distance in kilometers over which the rain rate R
i
applies. When examined in detail, this relationship is satisfactory for attenuations < 3 dB per kilometer; however, the higher attenuations exceed this prediction and agree with the relationship
$\gama = 0.055\langel R \rangel_{av}^{1.09}$
where
$\langel R\ rangel_{a v}$
is the path-average rain rate. Percent-of-time distributions are given for
$\langel R\ rangel_{a v},$
the attenuation, and the duration of attenuation. For this sample of data, the path attenuation exceeds thirty