CALIBRA WP200: Geophysics and modelling

WP200 activity covers the assessment of the ionosphere over Brazil and the development of an empirical forecasting ionospheric model taking advantage of the Total Electron Content (TEC) and scintillation data collected not only during CALIBRA but also with the fundamental contribution of the network established in the frame of the CIGALA project (hereafter CIGALA/CALIBRA network). INGV team, with the support of the other partners, carried out different activities to obtain a deep knowledge of the mechanism that rules the morphology and dynamics of the ionosphere over Brazil. First of all, an evaluation of the ionospheric phenomena impacting the high accuracy GNSS based applications by means of the tool for ionospheric climatology developed by INGV researchers was performed. Figure 4 gives an example of such analysis showing the climatological behaviour of the amplitude scintillation index S4 . This parameter is an indicator of the rapid variability of the satellite signal amplitude over a short time scale (typically 1 minute). In particular, Figure 4 reports the percentage of occurrence of S4 > 0.25 during the entire 2012. This analysis revealed a high degree of perturbation of the ionosphere over the region of São Paulo state highlighting the needs to investigate the relationship between different ionospheric parameters over this region. In particular, by applying a calibration method on the GNSS data from URTKN (UNESP Real Time Kinematic Network), INGV team investigated the correlation between TEC gradients in the ionosphere and scintillations (random fluctuations on the amplitude and phase of the signal received at ground) by means of the CIGALA/CALIBRA network receivers. In Figure 5 is shown an example of maps that describe the TEC (top panel) and its spatial gradients along North-South (middle panel) and East-West direction (bottom panel) during the period 04:20 to 04:30 UT (Local Time=UT-3 Hours) of the July 18th, 2012. White circles superimposed on the gradients maps indicate the locations where the scintillation index S4 0.25 was measured.

Starting from such climatological considerations, identification of the best location for the establishment of a Micro Test Area (MTA) was carried out in order to support the deployment of the new receivers for the improvements of the CIGALA/CALIBRA network coverage. A short-term forecasting model for TEC and scintillation parameters was developed with the support of SRC-PAS (Space Research Center, Warsaw). The preliminary version of the model forecasts the TEC. The refined version of the model extends the forecasting also to the scintillation parameters and increases significantly the accuracy in the forecasting. A test on the precision and accuracy of the model forecasting capability carried out using a large dataset, gives a statistical reasonability at the model output (Figure 6).

The near plans will focus mainly on the CIGALA/URTKN/MTA data analysis to support the refinement of the forecasting model. A closer interaction with WP300 is ongoing to tune the refined version of the model to the needs of the mitigation algorithms development.

Figure 4: Map of S4 percentage of occurrence above 0.25 in geographic coordinates (GPS + GLONASS, L1 frequency) in the UT range 22-04 UT.

Figure 5: 16 Jul 2012 between 4:20 UT and 4:30 UT (LT=UT-3): TEC (TEC units ,top), East-West TEC gradient (TECU/km, middle) and North-South TEC gradient (TEC/km, bottom). White circles represent the S4 index measured by PRU2 receiver. The diameter of the circles is proportional to the S4 value.

Figure 6: Time profiles (left plots) and corresponding distributions in logarithmic scale (right plots) of the differences between actual and forecasted values of S4 (a), σφ (b), TEC (c), p (d) and T (e) for the day 269/2013. Here σφ is the phase scintillation index, p is the slope of the phase PSD (power spectrum density), T spectral strength of the phase PSD at 1 Hz.