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Oblique Reflections of Mars Express MARSIS Radar Signals From Ionospheric Density Structures: Raytracing Analysis
Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.ORCID iD: 0000-0002-7933-0322
Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
Univ Iowa, Dept Phys & Astron, Iowa City, IA 52242 USA.
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2019 (English)In: Journal of Geophysical Research - Planets, ISSN 2169-9097, E-ISSN 2169-9100, Vol. 124, no 5, p. 1177-1187Article in journal (Refereed) Published
Abstract [en]

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar sounder on board the Mars Express spacecraft revealed oblique reflections coming systematically from apparently stable density structures in the Martian ionosphere. Although these were typically interpreted by assuming a straight line propagation of the sounding signal at the speed of light, the ionospheric plasma is clearly a dispersive medium. Consequently, the ray propagation paths may be significantly bent, and, moreover, the observed time delays need to be interpreted in terms of realistic group velocities of the signal propagation. We select a single particularly well-pronounced event with oblique reflections observable over a large range of signal frequencies, and we employ raytracing calculations to perform its detailed analysis. An isolated density structure responsible for the reflection of the sounding signal back to the spacecraft is assumed, and the relevant ionospheric signal propagation is properly evaluated. We show that initially oblique sounding signals get progressively more oblique during their propagation, imposing an upper threshold on the angular propagation distance between the spacecraft and the reflecting density structure, in line with the observations. Considering realistic propagation paths further allows us to explain the frequency dependence of the observed time delays and to accurately model the entire event. The obtained results are consistent with the spacecraft passing very close to a spatially limited density structure. We also show that the results obtained using realistic raytracing calculations are significantly different from the results obtained using additional simplifying assumptions.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION , 2019. Vol. 124, no 5, p. 1177-1187
Keywords [en]
MARSIS, Mars Express, Martian ionosphere
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:uu:diva-390047DOI: 10.1029/2018JE005891ISI: 000471600600003OAI: oai:DiVA.org:uu-390047DiVA, id: diva2:1340342
Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2019-08-05Bibliographically approved

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Andrews, David J.

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