The land mobile satellite radio channel between a satellite and a mobile terminal in a typical built-up environment is calculated via a constrained geometry-based model, i.e. replacing physical building facades by clusters of equivalent point scatterers. The properties of these scatterers (in terms of power density and angular spreading) are derived from the application of a physical ray-tracing tool including specular as well as dense multipaths in a canonical street canyon scenario. The proposed approach also incorporates a polarimetric model of diffuse multipath scattering.