METHODS OF AZIMUTH DETERMINATION AT A MAGNETIC REPEAT STATION - A COMPARISON

The determination of geographic azimuths is an essential step in field magnetic surveys. In spite of the relatively low precision required f or declination values, it is strongly recommended that those true azim uths should be measured with an error in the order of 0.1' to avoid co ntamination of desired magnetic values. The applicability and ease of use, as well the deficiencies of the various methods of azimuth determ ination must be considered in the light of the different field work co nditions encountered during repeat station surveys. In general, four c lasses of methods could be considered: geodetic, astronomical, use of a gyro-theodolite and use of a GPS system. The strengths and weakness of each of these methods are discussed and a comparison between them i s made. Notwithstanding a possible worldwide interest of this subject, a special emphasis is given to magnetic repeat station work in develo ping countries. As a conclusion, we could say that the most suitable m ethod for azimuth determination at a magnetic repeat station strongly depends on regional conditions. For developing countries (latitude ran ge between 30 degrees N and 30 degrees S), mainly for Latin American c ountries, the gyro-theodolite method proves to be very effective at th e present time.