The model is based on Pioneer Venus Orbiter (PVO) data from the orbiter electron temperature probe (OETP) from the first seven Venus years (12/78 - 12/82). About 35,000 data points are used to describe the electron density and temperature in the Venus ionosphere in the altitude range from 150 km up to the ionopause (about 500 km in daytime and about 3000 km at nighttime). Whereas an earlier model (Theis et al., 1980) used spherical harmonics to describe the solar zenith variation, this model uses error functions. Thirty-two coefficients are needed for the electron temperature model and 26 coefficients for the electron density.
R. F. Theis, L. H. Brace, and H. G. Mayr, Empirical Models of the Electron Temperature of the Venus Ionosphere, J. Geophys. Res. 85, 7787, 1980.
R. F. Theis, L. H. Brace, R. C. Elphic, and H. G. Mayr, New Empirical Models of the Electron Temperature and Density in the Venus Ionosphere with Applications to Transterminator Flow, J. Geophys. Res. 89, 1477, 1984.