Multidimensional free interpolation framework for high-precision modeling of slant total electron contents in mid-latitude and equatorial regions

Standard models of ionospheric delays have errors of order 1–8 TECU (standard total electron content units). On the basis of the free interpolation framework we propose a new simple model of the slant TEC distributions approximating slant TEC distributions obtained from the three-dimensional ionospheric models NeQuick2 and IRI-2016 with RMS error $<$ 0.05 TECU. The proposed model was tested for varios positions of receivers in mid-latitude and equatorial regions. Stability of the coefficients of the model with respect to the position of the receiver and time is substantiated.