Tomography of the lower troposhere using a small, dense network of GPS receivers

The application of tomographic techniques to the troposphere with GPS signals was demonstrated in previous work using data from the Kilauea permanent network, Hawaii. Local orography of the network considered there, however, played a key role in the resolution capabilities of the technique. The authors explore the possibilities of tomographic reconstruction of the four-dimensional (4D) structure of water vapor using a very small network of global positioning satellite (GPS) receivers with virtually no height differences between the stations. The analyzed campaign consisted of seven GPS receivers located at the Onsala Space Observatory, Onsala, Sweden, and was carried out in August 1998. Traditional meteorological data sources and tools such as the numerical weather model NCAR Mesoscale Model (MM5), satellite data from the National Oceanic and Atmospheric Administration (NOAA), Washington, DC, and data and analysis from the European Center for Medium-Range Weather Forecasting (ECMWF), Reading, UK, have been used to evaluate the results. A good agreement is found between GPS tomography and classical methods, even in meteorological situations with complex vertical structure of water vapo

Spatio-temporal tomography of the lower troposhere using GPS signals

The obtaining of the spatio-temporal representation of the wet refractivity distribution in the lower troposphere using GPS has been a line of research that has recently achieved very promising results. We here present a review of the work done and discuss some aspects as well as trace some future lines of development to increase the impact of GPS data in meteorological studies. Starting from the refinement of the tomographic technique, we assessed its capabilities using simulations based on the ground network of GPS receivers at mount Kilauea, Hawaii, and finally applied the whole procedure to the GPS data campaign conducted at the Onsala Space Observatory, verifying the results there obtained using traditional meteorological tools and analysis

Atmospheric signal propagation

GNSS satellites emit signals which propagate as electromagnetic waves through space to the receivers which are located on or near the Earth’s surface or on other satellites. Thereby, electromagnetic waves travel through the ionosphere and the neutral atmosphere (troposphere) which causes signals to be delayed, damped and refracted as the refractivity index of the propagation media is not equal to one. In this chapter, the nature and effects of GNSS signal propagation in both the troposphere and the ionosphere, is examined. After a brief review of the fundamentals of electromagnetic waves their propagation in refractive media, the effects of the neutral atmosphere are discussed. In addition empirical correction models as well as state-of- the-art atmosphere delay estimation approaches are presented. Effects related to signal propagtion through the ionosphere are dealt in a dedicated section by describing the error contribution of first up to third order terms in the refractive index and ray path bending. After discussing diffraction and scattering phenomena due to ionospheric irregularities, mitigation techniques for different types of applications are presented