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r~ <br />u <br />presentation to CMLRD within one year following cessation of subsidence. This reporting will no <br />longer be required. <br />The following is a description of the various phases of the subsidence monitoring program. <br />(1) Ground Survev Eight control monuments were established outside the zone of subsidence <br />to provide horizontal and vertical control for the area. Before each flight, the monuments were <br />panelled and re-levelled to determine their elevations by differential levelling or by using reciprocal <br />vertical angles. Panels had three or four arms, each 3 feet by 9 inches in size. Nine other points were <br />established outside the zone of subsidence and re-levelled prior to each flight to provide additional <br />vertical control. Map 131 shows the predicted subsidence contours and the 17 control points outside <br />the zone of subsidence. <br />Five additional control points were established inside the zone of subsidence. Three were established <br />along the axis of LW-1 and two were established over RP-5. These are also shown on Map 131. The <br />five monuments within the zones of subsidence were surveyed at the same time as the 17 control <br />points. Thereafter, the three "inside" monuments were surveyed every six months until the subsidence <br />was determined to have ceased. Semi-annual surveys of the "inside" monuments allowed BME to <br />determine when subsidence was complete. However, subsidence will probably continue for many <br />• years over RP-1. The elevations determined by the aerial monitoring techniques can also be <br />compared to those generated by on-theyround surveying. <br />(2) Aerial Photoaraohv Photography was taken at a scale of 1"=275' using black and white <br />film with a precise camera of 6-inch focal length. <br />(3) Analytical Aerial Triangulation This process was required to density and check the <br />ground control, using sophisticated simultaneous least square bundle adjustment software. <br />(4) Measurement of Regular Grid Digital Terrain Model fDTM) This was done using a highly <br />precise analytical stereoplotter. A grid boundary with grids oriented to the mining panels, was defined, <br />and the plotter driven automatically to X, Y (Fasting, Northing) coordinates at exactly 100' grid intervals <br />by a computer. At each point the stereo-0perator placed the measuring mark precisely on the ground, <br />after which the elevation was automatically recorded and stored together with the X, Y coordinates of <br />the point. Approximately 2800 points per square mile were measured. <br />BME proposed to determine elevations twice for the first set of photography. A comparison of the two <br />data sets were made so any significant discrepancies could be eliminated. This improved the <br />accuracy of the baseline data. <br />• Thliiterm Keview (~S~LtICJY) ~ifl-ES <br />