Rain measurements

It has been suggested that rainfall of ∼15mm/hr for 2-3 hours may be sufficient to trigger a dome collapse.
Radar provides a method for localised and frequent measurement of rainfall rate at the dome. This is not possible with conventional rain gauges which are situated remotely.
94GHz radar signals are very sensitive to rain since the drops are similar in size to the wavelength (below).
Modelling suggests that AVTIS 3 will be able to measure a 15mm/hr rainfall rate at ranges of up to ∼1km (bottom).

Illustration of effects of rain on a 94GHz radar

However, they are also heavily attenuated by rain which limits the
detection range. This presents a problem since the same reflectivity can be attributed to different rain rates for the same range (below).

Rain Reflectivity and associated rain rate

Measurement of rain rate therefore
requires an analysis of the radar returns across the entire range profile. Note this problem does not occur for conventional meteorological radar which operates at much longer wavelengths.

Radar return over range profile