Gradiometer based terrain estimation
First Claim
1. A terrain estimation system comprisinga gravity gradiometer providing measured values of gravity gradient;
- a memory storing terrain altitude data along a path to be traveled by said gradiometer;
location means for obtaining current location of said gradiometer during travel of said gradiometer along said path;
optimal filter means, operative in response to a statistical model of terrain and residual geology for calculating predicted values of gravity gradient to be sensed by said gradiometer at successive locations along said path, said terrain and said residual geology being based on data stored in said memory, gradiometer locations along said path being based on data obtained by said location means; and
wherein said filter means is operative further to compare measured and predicted values of gravity gradient to determine the presence of a deviation between measured and predicted values of gravity gradient, a nonzero value of the deviation being representative of an error in earth terrain data or in residual geology data or in gradiometer location data, said filter means being operative to null said deviation by correction of said earth terrain data or said residual geology data or said gradiometer location data.
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Abstract
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.
46 Citations
17 Claims
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1. A terrain estimation system comprising
a gravity gradiometer providing measured values of gravity gradient; -
a memory storing terrain altitude data along a path to be traveled by said gradiometer; location means for obtaining current location of said gradiometer during travel of said gradiometer along said path; optimal filter means, operative in response to a statistical model of terrain and residual geology for calculating predicted values of gravity gradient to be sensed by said gradiometer at successive locations along said path, said terrain and said residual geology being based on data stored in said memory, gradiometer locations along said path being based on data obtained by said location means; and wherein said filter means is operative further to compare measured and predicted values of gravity gradient to determine the presence of a deviation between measured and predicted values of gravity gradient, a nonzero value of the deviation being representative of an error in earth terrain data or in residual geology data or in gradiometer location data, said filter means being operative to null said deviation by correction of said earth terrain data or said residual geology data or said gradiometer location data. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 17)
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12. A method of estimating terrain comprising steps of:
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providing a map of known or presumed elevation data of a terrain; operating a gravity gradiometer to obtain measurements of gravity gradient; generating a statistical model of the terrain and residual geology and, via optimal filtering, obtaining a set of cross covariance terms from the statistical model; predicting values of gravity gradient from a sum of the cross covariance terms at a location of said gravity gradiometer relative to said terrain; comparing predicted and measured values of gravity gradient to obtain an innovation of gravity gradient; and adjusting a terrain estimate of the elevation data to reduce the innovation. - View Dependent Claims (13, 14, 15, 16)
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Specification