There are many methods, e. g. the Norwegian one documented in Gjertsen and Dahl (2002), for the blockage correction. In this method the number of beam traces are determined using altitude vertical angle, refractivity, atmospheric pressure, temperature data and data of water vapour partial pressure. This computed beam trace is used in a distributed model, where each point is taken in cylindrecal coordinate system if a point on the topografic map is higher than a computed one. The pre-calculated beam closest to the topografic data is used as minimum measurement height in that point.
