GRADIOMETER BASED TERRAIN ESTIMATION

A terrain estimation system and procedure in which prior knowledge of terrain configuration is taken as a starting point in the estimation procedure. The gravity field of the earth is sensed by a gradiometer which measures the gravity gradient as the gradiometer is transported by a moving platform past the earth's surface to obtain data of the topology of the earth's surface and of the geology of the terrain including subterranean oil and iron deposits. Optimal filter means, operative in response to a statistical model of terrain and residual geology predict values of gravity gradient to be sensed by said gradiometer at successive locations along a path of travel. Comparison is made between measured and predicted values of gravity gradient to update terrain altitude data by nulling a difference between measured values and predicted values of gravity gradient. Terrain surface is represented by the sum of a finite series of shells developed as cross covariance terms in a statistical mathematical model of terrain and residual geology. Each shell has a three-dimensional surface. A point on the surface of a shell is described by three parameters, namely the height of the point above a reference surface, north slope and east slope. A summation of shells of differing spatial frequency, such as a series of approximately one half dozen shells, provides for a smooth surface which represents the terrain at each of many points on the earth's surface.