ATP-3-09-02 Field Artillery Survey Download
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Survey Methods 16 February 2016 ATP 3-09.02 7-13 Determine the difference between 1900 and the time of observation. (Each hour is equal to 15°, and each 4 minutes is equal to 10.) Add if the observation time is after 1900, and subtract if the observation time is before 1900 (see figure 7-8 for an example). Figure 7-8. Determine the difference between 1900 and the time of observation Selection of Stars for Observation 7-35. The apparent motion of a celestial body has two components—a horizontal motion, representing change in azimuth, and a vertical motion, representing change in altitude. An error in measuring the altitude of a celestial body will result in a final azimuth error related to the ratio between the two components of the apparent motion of the body (see figure 7-9 on page 7-14). When a star is moving at a small angle to the horizon, an error in measuring the altitude will result in a greater error in final azimuth than it would if the star were moving at a large angle to the horizon (see figure 7-10 on page 7-14). This relationship is called the star rate, which is the ratio of resulting azimuth error to error in vertical measurement. A star that changes in altitude but not in azimuth will have a star rate of 0, since an error in altitude measurement will result in no error in azimuth. A star that changes so rapidly in azimuth and so slowly in altitude that a one mil error in attitude measurement will result in a 3 mil azimuth error.