GNSS in Practical Determination of Regional Heights

Abstract

Describing the position of a point in space, basically relies on determining three coordinate components: the Cartesian coordinates (X, Y, Z) in rectangular coordinate system or latitude, longitude and ellipsoidal height (φ, λ and h) in ellipsoidal coordinate system, referred to any given reference ellipsoid. Today, of course, global navigation satellite systems (GNSS) is the best and most popular method for determining φ, λ and h, directly. The instantaneous determination of position and velocity on a continuous base, and the precise coordination of time are included in the objectives of GNSS, and positioning with GNSS base on ranging from known positions of satellites in space to the unknown positions on the earth or in space. Besides the geometrically described coordinates however, the natural coordinates, the astrogeodetic latitude, longitude and orthometric height (, Λ, H), which directly refer to the gravity field of the earth, are preferable to take for many special purposes. In particular the orthometric heights above the geoid are required in many applications, not only in all earth sciences, but also in other disciplines such as; cartography, oceanography, civil engineering, hydraulics, high-precision surveys, and last but not least geographical information systems. Traditionally, these heights are determined by combining geometric levelling and gravity observations with millimetre precision in smaller regions. This technique, however, is very time consuming, expensive and makes providing vertical control difficult, especially in mountainous areas which are hard to access. Another disadvantage is the loss of precision over longer distances since each height system (regional vertical datum) usually refers to a benchmark point close to the sea level, which is connected to a tide gauge station representing the mean sea level (Hofmann-Wellenhof & Moritz, 2006).