Abstract: The present invention relates to terrain navigation wherein an earth-reflected satellite signal is received from at least one reference signal source whose position is known (120), for example a navigation satellite. Based on information contained in the received signal a measured estimate of a shortest reflection distance (d1(tb)) to the satellite (120) is derived. A relative spatial movement (?x, ?y, ?h) of a relevant craft (110) since a previous positioning instance (ta) is registered onboard the craft (110). Moreover, stored surface information is retrieved pertaining to an elevation (h1b) of the earth surface (130) in relation to the mean sea level (z0) at at least one geographical position (X1b, Y1b). Based on the relative spatial movement (?x, ?y, ?h) and the retrieved surface information at least one calculated estimate of the shortest reflection distance (d1(tb)) to the satellite (120) is derived.