Ground-based WVRs measure water vapor radiative
brightness temperatures which are converted into PWV using
retrieval coefficients [Hogg et al., 1983]. Retrieval coefficients
are calculated by regression analysis of radiosonde data, and
depend on climate and weather. Ground based WVRs provide
high temporal and poor spatial resolution because only a few
of these instruments are in use today. On the other hand, spacebased
down-looking WVRs perform well over oceans, poorly
over land, and provide high spatial and poor temporal resolution.