AATR an ionospheric activity indicator specifically based on GNSS measurements

Abstract

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.

Investigation of the Occurrence of Nighttime Topside Ionospheric Irregularities in Low-Latitude and Equatorial Regions Using CYGNSS Satellites

“…In our observational results, it should be noted that there was a more frequent occurrence in American longitudinal sector than that in Asian longitudinal sector during autumn season, which was agreement with their results shown in Juan et al [33] by using ground-based GNSS TEC data. Longitudinal dependence of seasonal distribution of ionospheric irregularity occurrence in the low-latitude and equatorial region has been a subject of intense research (see [28,[33][34][35]). Dymond [28] presented that seasonal distribution of equatorial ionospheric irregularity occurrence had a clear longitudinal dependence based on COSMIC observations.…”

“…Moreover, the equinoctial asymmetry in ionospheric vertical plasma drift speed and annual variation of plasma density also play a significant role in the generation of equinoctial asymmetry of ionospheric irregularity occurrence in the equatorial and low-latitude region [31,32]. In our observational results, it should be noted that there was a more frequent occurrence in American longitudinal sector than that in Asian longitudinal sector during autumn season, which was agreement with their results shown in Juan et al [33] by using ground-based GNSS TEC data. Longitudinal dependence of seasonal distribution of ionospheric irregularity occurrence in the low-latitude and equatorial region has been a subject of intense research (see [28,[33][34][35]).…”

Measuring phase scintillation at different frequencies with conventional GNSS receivers operating at 1 Hz

“…carrier-phase measurements, named cycle-slips (Takasu and Yasuda 2008;Liu et al 2018;Juan et al 2018b). These changes are not necessarily discontinuities, see, for instance, Fig.…”

Confirming geomagnetic Sfe by means of a solar flare detector based on GNSS

“…In our receiver selection, we excluded those receivers that could be affected by fast variations of STEC, such as scintillation, that would increase the uncertainties of the SF detections. In this sense, following Juan et al (2018), we excluded high latitude receivers and we used only the measurements from low latitude receivers gathered during the interval from 02:00LT to 18:00LT. For the computation of IPPs and the mapping function we used a single layer model for the ionosphere at 300 km of altitude.…”