Global Navigation Satellite Systems

Different Global Navigation Satellite System (GNSS) constellations are available these days. This has led to an increase in the number of satellites available for the user, and that presents different performance levels for the user requirements like accuracy and convergence time. However, these benefits come from different constellations that have different reference times and for some, different frequencies.

Precise Point Positioning (PPP) has been presented as being a position solution within a certain level of accuracy and precision.

The estimation of tropospheric zenith total delay (ZTD) and tropospheric integrated water vapour (IWV) from GPS observations, denominated as GPS meteorology, was initially proposed by Bevis et al. (1992). For troposphere studies, the tropospheric zenith wet delay (ZWD) can be obtained by simple subtraction from an estimated tropospheric ZTD of the tropospheric zenith hydrostatic delay (ZHD) computed by using pressure data, and a station’s latitude and height above mean sea level (Saastamoinen, 1972). Tropospheric IWV can then be computed by converting the tropospheric ZWD using temperature data.