Adaptive modelling of background noise for distance measurement

摘要

The invention relates to an improved method and an apparatus for navigating a craft (500) by means of remote distance measurement, for instance, via a radar altimeter. This measurement of a distance between the craft (500) and a surface (B) over which the craft (500) moves involves a measurement noise model (Ngnd(B)), which for particular geographical positions (Axy, Bxy; Cxy) designates an estimation of the surface's (A, B; C) inclination to cause measurement noise at remote distance measurement against the surface at the geographical position in question (Axy?, Bxy; Cxy). The measurement noise model (Ngnd(A), Ngnd(B); Ngnd(C)) thereby models surfaces of varying types and kown objects being located on the surface. Relevant measurement noise models (Ngnd(A), Ngnd(B); Ngnd(C)) are taken into account based on the georaphical area within which the craft (500) is estimated to be located. The size of this area is then limited iteratively by performing multiple consecutive remote distance measurements.