CHAPTER I, SECTION TA the intersection of observed angles from existing primary control stations. Periodic inspection trips were made prior to tests to determine that these stations were in place and a number of replacement stations were located. intervals totalling approximately 9,000 adjustment points. The relation between working points at the extremities of the lines was determined by first order traverse methoc:. Precise differential levels were run over the |: : with bench marks established at .pproximately 450-foot intervals. A horizontal line of sight was established by precise methods operating at night to minimize the effects of refraction. These line points were fet on observing towers at intervals along the ine. Vertical adjustments were accomplished by transferring elevations from the bench marks ge Figure 2-15. a aee 6. Measuring Chaining Bucks LOCATION OF STRUCTURES, The local controls in the various areas were satisfactory for layout of the majority of the Scientific Stations following the procedure outlined above. Figure 2-15 shows a precise measurement party at work and the equipment they used to measure between two chaining bucks. PIPE ARRAYS. The alignment of Stations 1203, 2220 and 2230 was an unusual survey assignment requiring the design of special equipment and establishing precise survey procedures to assure alignment within specified tolerances. Station 1203 consisted of 12 pipe lines 7,500 feet in length at varying grades and offsets. The linear relation between the working points at the extremities of the array was required to be within a tolerance of 1:25,000. The alignment of the centerline of each pipe was specified to be within a tolerance of plus or minus one inch from a true line of sight between working points. The pipes were supported on hangers providing for homzontal anc vertical adjustments at approximately 20-foot Page 2-44 So acne a ee ye ee en ha Figure 2-16. Vertical Alignment of Pipe Arrays