Ionosphere/Plasmasphere sounding with ground and space-based GNSS observations

Applying a methodology developed and tested in previous studies, the contribution from the ionospheric and plasmaspheric regions to the total electron content (measured by ground receivers) is analyzed. The method is based in the electron density profiles retrieved from radio occultations observed with low Earth orbit satellites, combined with an accurate empirical modeling of the topside-ionosphere electron density. The results of a climatological study of the fractional electron content from the ionospheric region are presented for a year of low solar activity. It is shown that a simple parametric model can be used to reproduce the electron content variations in the ionosphere and the plasmasphere between sunrise and midday, the period of the day showing the largest electron content variability.Peer ReviewedPostprint (author's final draft

Real time Ionospheric determination at global scale

The global ionospheric determination has been possible in the last 15 years thanks to the availability of a new type of ionospheric sensor with a very high spatial and temporal sampling: the dual-frequency GPS receivers. Indeed, several hundreds of them, worldwide distributed, are freely available, tracking typically 6+ GPS satellites in view, providing at every epoch several thousands of line-of-sight integrated free electron densities (Slant Total Electron Content, STEC). This has allowed in particular to compute and freely distribute global Vertical Total Electron Content (VTEC) maps, in the context of the open- product organization called International GNSS Service (IGS), which applications run from single frequency receivers (accurate mitigation of ionospheric delay), calibration of new altimeters (such as the SMOS mission) up to the potential use for increasing the performance of positioning based on carrier phase measurements. One of the next challenges, in particular in IGS, is computing the global VTEC maps, in real-time, which involves much less permanent receivers, increasing much more the di cult task of interpolating in a realistic way the electron content over large regions with few receivers (south hemisphere, oceans...). In this paper the actual status of the problem will be presented, from the perspective of gAGE/UPC, one of the four IGS Ionospheric Analysis Centers, participating in the Real-Time IGS Pilot Project.Peer ReviewedPostprint (published version

Navegando con satélites : (o cómo posicionarse con GPS y Galileo con errores de pocos centímetros, en tiempo-real y a escala continental)

Peer Reviewe

Synthetic events description, generation and characterization report

Preprin

Fast-PPP assessment in European and equatorial region near the solar cycle maximum

Oustanding Student Poster Award, European Geosciences Union General Assembly, 2014Award-winningPostprint (published version

ESTB performance against lossing satellites (first results)

The EGNOS System Test Bed (ESTB) is the EGNOS prototype which has been broadcasting a Signal in Space since February 2000. Accuracy, integrity, continuity and availability are the main concepts in this European component of the Satellite Based Augmentation System which is designed to support en route through precision approach aircraft navigation. In this work, for the first half of the year of 2002, we study the ESTB performance in fixed sites in Barcelona, and we analyze how this performance is affected when losing a single ESTB monitored satellite. The data set involves a 24 hours weekly measurements collected in two fixed sites (UPC1 and UPC2), from January to August 2002. In particular, the number of Loss of Integrity events (LOI) and the degradation of the Vertical Position Error percentile and the APV-II availability are analyzed. As the main results, two satellites have been identified which loss could have produced a large number of LOIs (up to hundreds) in two particular days before the ESTB update of April 16th 2002. The improvement in the ESTB performance after such update is also reported.Peer Reviewe

GPS differential code biases determination: methodology and analysis

The final publication is available at Springer via http://dx.doi.org/10.1007/s10291-017-0634-5We address two main problems related to the receiver and satellite differential code biases (DCBs) determination. The first issue concerns the drifts and jumps experienced by the DCB determinations of the International GNSS Service (IGS) due to satellite constellation changes. A new alignment algorithm is introduced to remove these nonphysical effects, which is applicable in real time. The full-time series of 18 years of Global Positioning System (GPS) satellite DCBs, computed by IGS, are realigned using the proposed algorithm. The second problem concerns the assessment of the DCBs accuracy. The short- and long-term receiver and satellite DCB performances for the different Ionospheric Associate Analysis Centers (IAACs) are discussed. The results are compared with the determinations computed with the two-layer Fast Precise Point Positioning (Fast-PPP) ionospheric model, to assess how the geometric description of the ionosphere affects the DCB determination and to illustrate how the errors in the ionospheric model are transferred to the DCB estimates. Two different determinations of DCBs are considered: the values provided by the different IAACs and the values estimated using their pre-computed Global Ionospheric Maps (GIMs). The second determination provides a better characterization of DCBs accuracy, as it is confirmed when analyzing the DCB variations associated with the GPS Block-IIA satellites under eclipse conditions, observed mainly in the Fast-PPP DCB determinations. This study concludes that the accuracy of the IGS IAACs receiver DCBs is approximately 0.3–0.5 and 0.2 ns for the Fast-PPP. In the case of the satellite DCBs, these values are about 0.12–0.20 ns for IAACs and 0.07 ns for Fast-PPP.Peer ReviewedPostprint (author's final draft

SBAS ionospheric performance evaluation tests

Satellite Based Augmentation systems (SBAS) provide to Global Navigation Satellite Systems (GNSS) users with an extra set of information, in order to enhance accuracy and integrity levels of GNSS stand alone positioning. In this context, different test methods to analyze the ionospheric corrections performance are presented. The first set of tests involves two of the ionospheric calculations that are applied daily to the Global Ionospheric Maps (GIM), computed by the IGS Associate Analysis Centers: a TEC TOPEX comparison test and the STEC variations test. The second family of tests provides two very accurate analyses based on large-baselines ambiguity resolution techniques giving comparisons for absolute STEC and double differenced STEC determinations. Those four analyses have been applied using EGNOS System Test Bed (ESTB) data showing some satellite dependent biases.Peer Reviewe

AATR an ionospheric activity indicator specifically based on GNSS measurements

This work reviews an ionospheric activity indicator useful for identifying disturbed periods affecting the performance of Global Navigation Satellite System (GNSS). This index is based in the Along Arc TEC Rate (AATR) and can be easily computed from dual-frequency GNSS measurements. The AATR indicator has been assessed over more than one Solar Cycle (2002–2017) involving about 140 receivers distributed world-wide. Results show that it is well correlated with the ionospheric activity and, unlike other global indicators linked to the geomagnetic activity (i.e. DST or Ap), it is sensitive to the regional behaviour of the ionosphere and identifies specific effects on GNSS users. Moreover, from a devoted analysis of different Satellite Based Augmentation System (SBAS) performances in different ionospheric conditions, it follows that the AATR indicator is a very suitable mean to reveal whether SBAS service availability anomalies are linked to the ionosphere. On this account, the AATR indicator has been selected as the metric to characterise the ionosphere operational conditions in the frame of the European Space Agency activities on the European Geostationary Navigation Overlay System (EGNOS). The AATR index has been adopted as a standard tool by the International Civil Aviation Organization (ICAO) for joint ionospheric studies in SBAS. In this work we explain how the AATR is computed, paying special attention to the cycle-slip detection, which is one of the key issues in the AATR computation, not fully addressed in other indicators such as the Rate Of change of the TEC Index (ROTI). After this explanation we present some of the main conclusions about the ionospheric activity that can extracted from the AATR values during the above mentioned long-term study. These conclusions are: (a) the different spatial correlation related with the MOdified DIP (MODIP) which allows to clearly separate high, mid and low latitude regions, (b) the large spatial correlation in mid latitude regions which allows to define a planetary index, similar to the geomagnetic ones, (c) the seasonal dependency which is related with the longitude and (d) the variation of the AATR value at different time scales (hourly, daily, seasonal, among others) which confirms most of the well-known time dependences of the ionospheric events, and finally, (e) the relationship with the space weather events.Postprint (published version