Assessing the potential of EnVision's Subsurface Radar Sounder for detecting Venusian lightning

The European Space Agency's EnVision mission, slated for launch in the next decade, will provide unprecedented insights into the geological and atmospheric dynamics of Venus. EnVision's primary objectives include high-resolution subsurface mapping with the Subsurface Radar Sounder (SRS), operating with 9 MHz as the central frequency. This study investigates the potential of SRS to detect electromagnetic waves generated by lightning in the Venusian atmosphere, a phenomenon whose existence remains debated. While optical observations of lightning are hampered by Venus's dense cloud cover, previous missions like the Pioneer Venus Orbiter and the Venus Express have detected whistler mode waves, which may be indicative of lightning activity. This research employs the Stanford Full-Wave Method to model the propagation of lightning-induced waves in the SRS frequency range. This procedure allows us to establish if a radio signal generated at the cloud level at about 50 km altitude could propagate in the ionosphere and reach the radar with detectable power. The model has been previously applied to signals with frequencies up to 100 Hz in the Venusian atmosphere. Now, it is being adapted for the propagation of radio waves up to the MHz frequency band. By simulating various scenarios involving different ionospheric conditions - including the presence of ionospheric “holes” - magnetic field strengths and discharge intensities and rates, we assess the detectability of these signals by the SRS. Our findings confirm the sensitivity of wave propagation to variations in the Venusian ionosphere's electron and ion density profiles, identifying critical magnetic field thresholds required for successful detection. The model is also being extended to lightning phenomena on Earth to study their detectability from space in the MHz frequency range under known background conditions. This study contributes to our understanding of Venus's atmospheric processes and provides valuable context for interpreting potential lightning signatures in EnVision's SRS data.