do not agree with those obtained from GPS on the mm-accuracy
level. Thus, if such ray-traced corrections are applied, one has to
model the bias of the numerical weather model, similar to the
mapping function approach. Since it can be anticipated that
numerical weather models are representing the azimuthal
asymmetry of the troposphere around the station well, one has
to concentrate only on the determination of these biases. Moreover,
as it can be assumed that such a time-varying bias grows with decreasing elevation angle e, it is possible to estimate these model deficits similar to the mapping function approach.