Amalia Meza

A New Ionosphere Monitoring Technology Based on GPS

Although global positioning system (GPS) was originally planned as a satellite-based radio-navigation system for military purposes, civilian users have significantly increased their access to the system for both, commercial and scientific applications. Almost 400 permanent GPS tracking stations have been stablished around the globe with the main purpose of supporting scientific research. In addition, several GPS receivers on board of low Earth orbit satellites fitted with special antennas that focus on Earths horizon, are tracking the radio signals broadcasted by the high-orbiting GPS satellites, as they rise and set on Earth horizon. The data of these ground and space-born GPS receivers, readily accessible through Internet in a ‘virtual observatory’ managed by the International GPS Service, are extensively used for many researches and might possibly ignite a revolution in Earth remote sensing.By measuring the changes in the time it takes for the GPS signals to arrive at the receiver as they travel through Earths atmosphere, scientists can derive a surprising amount of information about the Earths ionosphere, a turbulent shroud of charged particles that, when stimulated by solar flares, can disrupt communications around the world. This contribution presents a methodology to obtain high temporal resolution images of the ionospheric electron content that lead to two-dimensional vertical total electron content maps and three-dimensional electron density distribution. Some exemplifying results are shown at the end of the paper.

Comparing vertical total electron content from GPS, Bent and IRI models with TOPEX-Poseidon

Abstract The Global Positioning System (GPS) has become a powerful and mature geodetic tool widely used for a broad range of technological and scientific applications. The observations of permanent GPS tracking stations, under the management of the International GPS Service (IGS), seem suitable for ionospheric research, providing continuous and quite good world-wide coverage at low cost for the users. TOPEX-Poseidon surveys sea-level heights by measuring the time required for pulses generated by the onboard radar altimeters to bounce back to the satellite from the sea surface. Free electrons in Earths ionosphere can delay the return of the radar pulses to the satellite, interfering with the accuracy of sea-level measurements. To correct this delay, the satellites altimeter makes measurements in two channels. The difference between the two measurements provides a measure of the integrated total electron content, between satellite and sea surface. To analyse the quality of different vertical total electron content (VTEC) maps, we compare our empirical model of the VTEC obtained using GPS data (hereafter called La Plata model) with the VTEC measurements of TOPEX-Poseidon and with the VTEC obtained using the Bent and IRI models. The Bent and IRI models provide monthly averages in the non—auroral ionosphere for magnetically quiet conditions and they are ones of the classical global ionospheric models used as referent in many ionospheric researches. On other hand we have that La Plata model provides a numerical ionospheric model at “any time” using GPS measurements; in disturbed magnetic activity it provides also a mean representation of ionosphere that are very different that in quiet conditions. We make comparison between the different models in quiet geomagnetic conditions because Bent and IRI models were developed to work in these conditions. So in this study we chose some selected quiet geomagnetic days during the year 1997. In our analysis we can see that the GPS model has the best global VTEC representation at any latitude and longitude even without modelling the ionospheric anomaly.