Solar Occultation Experiments (SOE) in the Venusian Atmosphere: effect of orbital parameters on the spatiotemporal distribution of measurements

Solar occultation is a satellite-based technique for high-resolution vertical profiling of planetary atmospheres. Owing to the distinctive observational geometry, the deduction of the spatiotemporal coverage of solar occultation measurements as a function of the spacecraft orbit is non-trivial. In this work, we have implemented python-based 3D simulations of the occultation-viewing geometry for a hypothetical Solar Occultation Experiment (SOE) to study the atmosphere of Venus. The simulations incorporate planetary motions and orbital propagation using the astropy and poliastro packages, and compute the instantaneous line-of-sight (LoS) tangent point using 3D vector algebra. SPICAV/SOIR data from Venus Express was used to validate the simulations, showing excellent agreement. Using the simulations, we conducted a first-of-its-kind theoretical study on the effect of varying different spacecraft orbital elements on the spatiotemporal distribution of solar occultation measurements in the Venusian atmosphere, confirming a highly sensitive dependence. The semimajor axis (a) and inclination (i) of the spacecraft orbit are found to influence the latitudinal extent of observations and the nature/duration of occultation seasons, while the eccentricity (e) and argument of periapsis (ω) determine the distinct regions of sparse observations. The spatiotemporal spread of individual SOE profiles is found to depend on the orbital parameters as well as the solar beta angle. Our results show that spacecraft orbits can be designed with appropriate parameters to optimize the coverage of SOE measurements in view of achieving specific science goals, providing valuable inputs for future missions to Venus that aim to implement the solar occultation technique.