Earth Strain Measurements with the Transportable Laser Ranging System: Field Techniques and Planning (Final Report, NASA Contract NAS 5-25897)
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We have conducted a feasibility study to examine the potential of the Transportable Laser Ranging System (TLRS) for monitoring the ground deformation around satellite ranging stations and other geodetic control points. Emphasis has been placed on testing the usefulness of the relative lateration technique. The temporal variation of the ratio of the length of each survey line to the mean length of all survey lines in a given area is directly related to the mean shear strain rate for the area. The data from a series of experimental measurements taken over the Los Angeles basin from a TLRS station at Mt. Wilson show that such ratios can be determined to an accuracy of one part in 107 with a measurement program lasting for three days and without using any corrections for variations in atmospheric conditions. A numerical experiment using a set of hypothetical data indicates that reasonable estimates of the present shear strain rate and the direction of the principal axes in southern California can be deduced from such measurements over an interval of one to two years. Thus, the relative lateration from the TLRS appears to be a very economical way to monitor ground deformations, although there has: been no opportunity yet to measure the actual ground strain by reoccupying the Mt. Wilson site.