STUDYING THE ACCURACY OF ELEVATION MEASUREMENTS IN THE POSITIONING SYSTEM GNSS IN COMPARISON OF CONVENTIONAL LEVELING METHODS

The paper includes the study of the accuracy of the measurement of heights and levels of points on the surface of the earth using the Global Navigation Satellite System (GNSS) to study the possibility of replacing the Conventional Method (CM) which is one of the most cost-effective and requires a lot of time, effort and cost. GNSS monitoring made a qualitative development in the implementation of cadastral work. The three dimensional coordinates of Y, Z and X is obtained for points on the surface of the earth directly and with acceptable accuracy. These coordinates are calculated on the surface of the reference Ellipsoid (WGS-84). However, the heights used in all surface and mapping work are calculated from the mean sea level (MSL) and this surface is not compatible with GNSS measurements. To convert the measurement of altitude between the reference surfaces mentioned above, it is necessary to know the difference between the height of the geoid (h) and the height of the ellipsoid (H) at the point of measurement required. This difference is called Geoid Undulation and is denoted by (N). Geoid elevations are taken from the Global Geoid Models (GGM) available on the Internet. Such as the Global Geoid Model (EGM2008) currently used to improve the accuracy of the height measurement results by (GNSS). However, the accuracy of these models does not suit the precision work of engineering projects. The possibility of raising the accuracy of the numerical separation calculus (N) was carried out by creating additional field observations in the limited area of work and calculating the Local Geoid Model (LGM) and thus raising the accuracy of the measurement results of the height of the satellite system