| 摘要 |
A first image of the side wall is made from the drill bit and a second image of the internal wall of the shaft is made after removal of the drill bit. This second image is indexed with respect to a second reference linked to the ground medium. The first and second images are calibrated relative to each other and the first image is indexed with respect to the first - The second reference is in X, Y and Z coordinates, where Z is defined along the axis of the shaft and X in the direction of magnetic North. The first and second images are obtained by measuring the layers, using conductivity, resistivity, magnetic sensitivity and/or acoustic reflectivity. In addition at least the radial component of the direction of magnetic remanence from the drill is determined to define paleo North and thus a first reference linked to the drill in x, y and z coordinates (z is along the axis of the drill and z is in the direction of paleo North). The angle alpha between magnetic North and paleo North is determined. The orientation of a second drill bit in a shaft where the second image cannot be taken can be calculated where the second shaft is near the first and alpha is known for the second shafts. The orientation can then be determined by finding the direction of paleo North in the first shaft and indexing the first drill by positioning its paleo North relative to magnetic North until alpha is the same as that in the second shaft. When the first shaft is surrounded by a number of second shafts, the value of alpha is obtained by interpolation between the angles alpha measured by the second drill bits. The method includes measuring a parameter defining a spatial datum for the ground medium along the axis of a shaft, for example natural gamma radiation.
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