Evaluation of passive radio sounding of icy moons based on a radar equation
Year: 2026
Type: preprint
Abstract: Passive radar sounding is one of the ways to observe surfaces and subsurfaces of planetary objects through reflection of natural radio emissions. Using observations of Radio and Plasma Investigations (RPWI) aboard Jupiter Icy Moons Explorer (JUICE), we have a plan to apply this technique to observe Jovian auroral radiation reflected on icy moons. For feasibility studies, we derived an expanded radar equation for planetary radio waves reflected on the moon’s surface, including the loss due to the moon’s spherical shape and scattering by surface roughness. Using this equation, we estimated the power and polarization characteristics of reflected radio emissions in two cases; terrestrial auroral kilometric radiation (AKR) reflected on the lunar surface and Jovian Hectometric radiation (HOM) reflected on the Ganymede surface. We showed the quantitative feasibility of the observation capability and potential of polarization measurements for detecting the permittivity of a surface. Additionally, we compared the estimation of the lunar case with a real case of AKR reflection observed using Lunar Radar Sounder (LRS) aboard Kaguya. The observed power ratio of reflected AKR to incident one was 2–5%, estimated from the interference fringe in the observed frequency-time diagram. This observed value agreed with the estimation from our radar equation.
Source: Research Square
Institution: Tohoku University
Language: English
Topic: Astro and Planetary Science
Subfield: Space and Planetary Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7225631357