surveying iii (topographic and geodetic surveys) - Modern Prepper

observation, contains a light source which can be activated electronically for photographic purposes.Large satellites with no independent source of illumination can be photographed at dusk or dawn whenreflected sunlight illuminates the vehicle. The smaller angular distances between the images of thesatellite and the star background are measured, and these measurements are used to determine thedirection of the satellite from the observation point.(b) The SECOR system employs a series of transmitting and receiving stations on the groundwhich contact a specially equipped satellite as it passes within range. Command signals are transmittedfrom the ground to the satellite. When it receives the command signal, the satellite transmits a rangingsignal back to the ground station. The distance to the satellite can thus be assured by comparing theoutgoing signal with the incoming signals at the ground station. Various corrections must be made foratmospheric effects. Four practice stations are used on the ground. Three of these stations are locatedon a known datum, and the fourth at an unknown position (Figure 1-12). A series of simultaneousmeasurements are made from each ground station during each pass of the satellite. These measurements,when converted, establish the position of the satellite and the position of the unknown station. Theunknown station can be located from 100 to 1,500 miles from the known stations. Although the SECORsystem is still in the improvement stage, results of reduced data already indicate that it will be a firstordergeodetic tool.Figure 1-12. SECOR Ranging of SatelliteEN0593 1-16