A novel technique for plasma asymmetry correction in radio occultation profiling

Radio Occultation (RO) experiments often employ the geometrical optics (GO) approximation and the Abel transformation, assuming spherical symmetry of the planetary atmosphere or ionosphere to retrieve electron density profiles. This assumption is also extended to derive temperature, pressure, and neutral density profiles of the lower atmosphere. However, the assumption of spherical symmetry is not always valid and can introduce significant uncertainties in the retrieved electron density profiles. This study proposes a simple retrieval algorithm that accounts for ionospheric asymmetry and demonstrates the effect of solar zenith angle (SZA) variation along the ray path. Unlike traditional methods, it does not rely on the Abel transformation and avoids the assumption of spherical symmetry, making it applicable under diverse geophysical conditions. The method is applied to RO observations around Venus, obtained from the Akatsuki and Venus Express (VEX) radio science experiments. It assumes that plasma is primarily produced by solar radiation and follows the distribution: $N\left(sza\right)=N_0\times {\left(\frac{cos\left(sza\right)}{cos\left(sz{a}_0\right)}\right)}^k$, where $N_0$ is plasma density at $sz{a}_0$, and k = 0.454. Results indicate that using the spherical symmetry assumption overestimates the main peak electron density by 2%–5% and the electron density at lower altitudes by 400%–800%. The proposed method offers a more accurate framework for retrieving electron density profiles, particularly in regions where the spherical symmetry assumption breaks down.