A novel piecewise linear transformation to moderate regional boundary effect on Real-Time regional ionospheric map (RT-RIM)

[Display omitted] •A novel piecewise linear transformation-adjusted spherical cap harmonic (PLT-ASCH) method is proposed to alleviate the severe impacts of uneven and sparse IPPs distribution and boundary effect on the RT-RIM modeling accuracy.•PLT-ASCH method can transform the IPPs into a hemisphere with nearly uniform distribution by employing PLT to cap-longitude and −latitude.•The modeling accuracy near the boundary of the mapping zone is further improved through a compensation scheme for the southern hemisphere.•Comprehensively considering the modeling accuracy and robustness as the key factors of the RT-RIM application, the strategy of the core PLT-ASCH parameters determination is proposed to improve the ionospheric modeling applicability of PLT-ASCH method on dense and sparse IPPs distribution for low-middle-high latitude areas. RT-RIM with high accuracy and dense spatiotemporal resolution of the ionospheric total electron content is crucial to diverse real-time GNSS applications. However, the uneven ionospheric pierce points distribution and boundary effect severely restrict the RT-RIM accuracy. We dedicate to the rapid and straightforward method to address the limited accuracy issue caused by the two crucial challenges. A novel piecewise linear transformation-adjusted spherical cap harmonic (PLT-ASCH) method is proposed to moderate the localized accuracy decrease in various latitudes areas for both active and stable ionospheric conditions. Especially, in the active ionospheric condition, the RMS improvements referring to IGS products are about 38.85%, 17.04%, 16.73% in Europe and 53.12%, 4.36%, 4.35% in South America, comparing to the inverse distance weighting, ASCH, and adjusted spherical harmonics adding Kriging methods. Moreover, the RMS improvements referring to differential slant TEC are about 48.11%, 16.53%, 16.99% in Europe and 61.01%, 4.87%, 4.33% in South America.