For the detection of Travelling Ionospheric disturbances, eight complementary methodologies are applied in the TechTIDE project with real-time and historical data from Digisonde DPS4D ionospheric sounders, from the Continuous Doppler Sounding System and from GNSS receivers.
- HF-TID method
- CDSS-MSTID detection method
- GNSS TEC gradient algorithms
- Spatial and Temporal GNSS analysis
- The AATR indicator
- HF Interferometry method
- HTI technique to monitor wave activity
- TaD 3D mapping of the electron density
4. Spatial and Temporal GNSS analysis
(Hernández-Pajares et al., 2006)
The procedure to detect and to characterise TIDs, including velocity and period will be based on the Spatial and Temporal analysis of GNSS measurements (Hernández-Pajares et al., 2006). This procedure allows the study of any ionospheric perturbation (including MSTID or LSTID) and can be used for detecting the TID (with a single receiver) or estimating the propagation parameters (from a network of receivers). The basic GNSS measurement used is the geometry-free combination of carrier phases, with measurement noise at the level of few millimetres. The first step for the TID detection is to detrend the data in order to remove the well-known dependences, such as diurnal and elevation angle variations, having larger time scales than the TID. This detrending can be applied in real-time and for a single receiver. Therefore, information about the TID occurrence can be obtained for the monitored region (around the receiver).
Figure 4 shows for three different receivers the original measurements, top plot, and the detrended data, bottom plot. The baselines are less than 40 km, clearly under the MSTID wavelength.
After detrending the measurements, it is possible to detect, in any of the receivers, the fluctuations associated with the TIDs. Moreover, correlating these fluctuations on the different receivers in the network, it is possible to estimate the propagation parameters (propagation direction, velocity and amplitude). The same procedure can be applied for LSTIDs and MSTIDs, but, for the detrending, one has to take into account the characteristic periods of these two TIDs.
Hernández-Pajares, M., J. Miguel Juan Zornoza, Jaume Sanz, “Medium Scale Traveling Disturbances Affecting GPS Measurements: Spatial and Temporal Analysis”, JGR, Vol.111, A07-S11, 2006, (doi:10.1029/2005JA011471).