Abstract

Sun Observation for Azimuth: An Error Analysis Framework
Track: Education
Authors: Jerry Nave, Tarig Ali

Sun observations provide a robust way for determining the geodetic or true azimuth at an area through the accurate estimation of the astronomic azimuth. True azimuth is the horizontal angle between the geodetic or true north and the survey line of interest. Geodetic or true north is a direction determined from a mathematical approximation of the earth's shape while astronomic north is based on the direction of gravity and the axis of rotation of the earth, and is normally determined using the sun or north star "Polaris" location. There are two methods for determining an azimuth by observing the sun; the first is known as the altitude method and the second is called the hour angle method. The basic difference between the two is that, the altitude method requires the determination of an accurate vertical angle, whereas the hour angle method re¬quires the determination of very accurate time. The hour angle method is more popular due to the fact that it is more accurate, has fewer restrictions on time of day and geographic location, more flexible, and is appli¬cable to the Sun, Polaris and other stars. In this article, an analysis of the errors involved in the process of determining the true azimuth of a line by observing the sun using the hour angle method is presented. A Gauss-Markov model is used to represent the error in the true azimuth estimation process. Six sets of sun observation for azimuth data (three with telescope direct and three reverse) horizontal Circle's readings were used in order to estimate the true azimuth of a line at the location mentioned above.