4 research outputs found
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