Perspectives of Cost-Efficient GNSS Equipment for Wide-Spread and High-Quality Meteorological and Positioning Applications

Abstract

Whether in cars, smartphones, watches or fitness-trackers - the use of Global Navigation Satellite Systems (GNSS) has become a part of our daily life. Currently there are more than 100 GNSS satellites in orbit. They are routinely utilized for positioning and timing purposes, but their signals can also be used to monitor our environment. The basic principle GNSS measurements rely on is measuring the time difference between the transmitted signal of the satellite antenna and the receiving antenna (typically on the ground). While propagating through the atmosphere, the signal is delayed by the physical properties of the particles in its various layers. This delay is traditionally seen as undesired noise that should be eliminated from the data. This noise however also includes information about the state of the atmosphere which can be described by various parameters. One of such parameters is the delay caused by the 'wet' particles (predominantly water vapor) in the troposphere (lower 20km of the atmosphere). Weather models can use this information to correct the amount and location of atmospheric humidity which has proved to be beneficial for rainfall forecasts. To extract this information from the total signal delay, the delay caused by the ionosphere (upper part of the atmosphere, up to about 1000km) must be eliminated. A standard method is to make use of the dispersive character of the ionized particles in this layer and to eliminate the majority of this error by forming a so-called ionosphere-free linear combination. This requires signals on at least two different frequencies. Traditionally, only geodetic instruments e.g. utilized as permanent ground receivers operated by (inter-) national organizations use hardware that track GNSS signals on at least two frequencies. Such receivers are expensive (in the order of several thousand Euros) and as a result many GNSS networks outside developed areas lack the station density that is needed to capture the complex distribution of atmospheric water vapor. A densification for meteorological purposes with geodetic-grade GNSS receivers and antennas is economically not feasible. Similarly, local precision positioning equipment is not accessible for many regions, foremost situated in the Global South, due to the coarse distribution of static GNSS ground stations and expensive equipment to perform surveying tasks. Technological advances in recent years enabled the release of cost-efficient single- and dual-frequency GNSS receivers and antennas which may offer an alternative to the high-grade technology. However, the use of consumer-grade hardware is associated with challenges that need to be overcome. In this thesis, the performance of low-cost GNSS receivers in combination with antennas of a range of different type and qualities for high-precision applications was analyzed. In particular, the efficiency of using this equipment for meteorological and positioning applications was experimentally quantified and methods to enhance their performance were developed and implemented.