eSWua IONORING tool: vTEC computation

sTEC values are mapped as a two-dimensional surface by means of the classical thin shell method and the values of vTEC are obtained by projecting sTEC to the vertical at the IPP and by considering the shell height at 350 km. The IPP coordinates are calculated in the WGS84 reference frame by using the positions of the receivers (derived from RINEX files) and of the satellites. The latter are evaluated by leveraging on the navigation information broadcasted by each receiver in its NTRIP streaming or alternately, from the IGS navigational information streaming. To produce a vTEC map in which the impact of the noise on code measurements is mitigated, vTEC values estimated at every IPP from all considered satellite-receiver pairs are interpolated through a non-parametric local regression technique named LOWESS, which is an interpolation method that includes local data in the computation of the smoothing curve. The LOWESS interpolation algorithm is first applied on the whole vTEC dataset to identify and reject outliers and then it is reapplied on the clean dataset to provide the final vTEC map that is provided in therms of the smoothed vTEC curve evaluated on a regular grid.