### Abstract

- Top of page
- Abstract
- 1. Introduction
- 2. Fundamentals
- 3. VTEC Model Approaches
- 4. Comparisons
- 5. Conclusion and Outlook
- References
- Supporting Information

[1] Most of the geodetic ionosphere models describe the electron density of the Earth's atmosphere by global maps of the vertical total electron content (VTEC) for fixed time intervals (e.g., 2 h) assuming a single-layer model and using a spherical harmonic expansion up to a specific degree *n*. However, it is well known that spherical harmonic models are not suited for representing data of heterogeneous density and quality. As a consequence, data gaps cannot be handled appropriately. In this paper we present a different approach for modeling VTEC generally depending on space and time defining the 3-D system of base functions as tensor products of trigonometric B spline functions for the longitude and two sets of endpoint-interpolating B spline functions for latitude and time, respectively. We compare this approach to a spherical harmonic expansion with similar resolution and show how data gaps influence the accuracy of VTEC maps even in areas with good data coverage.