A method of transferring G.T.S. benchmark value to survey area using electronic total station

Abstract

A G.T.S. (Great Trigonometrical Survey) benchmark is a permanently fixed reference survey station (or point), having known elevation with respect to a standard datum (mean sea level). These are established all over India by Survey of India department with greater precision. A benchmark value is quite essential at any survey area, especially for reduction of observed sea level with respect to mean sea level or chart datum (CD). While carrying out bathymetric survey of a survey area, the datum referenced values thus obtained are used to compute the final depth contours of the survey area (with respect to CD). So, a benchmark, having known elevation is quite essential at the survey area, without which, preparation of a bathymetric chart is impossible. In some places, GTS benchmarks are available within a kilometer distance and can be easily transferred to the survey area by fly leveling using an automatic Level instrument and a graduated leveling staff. But in most of the cases, GTS benchmarks may be at far away distance from the area to be surveyed. In these cases, the most common traditional method of transferring the benchmark value using an automatic level instrument is a difficult task, consuming enormous amount of time and labour. To eliminate this process, a method is suggested in this technical report to transfer GTS benchmark from any far distance to the survey area. A latest Electronic Total Station (ETS) is the instrument that can be used for this purpose. The main advantage in applying this method is that considerable amount of time can be saved while maintaining the required accuracy