A first demonstration of Mars crosslink occultation measurements

Abstract

A series of three crosslink occultation experiments have been acquired between the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft to probe the Martian atmosphere in 2007. While crosslink occultations between Earth‐orbiting satellites have been used to profile the Earth's atmosphere and ionosphere since 1995, this represents the first demonstration of crosslink occultation measurements at another planet. These measurements leverage the proximity link telecommunication payloads on each orbiter, which are nominally used to provide relay communication and navigation services to Mars landers and rovers. Analysis of the observed Doppler shift on each crosslink measurement reveals a clear signature of the Martian atmosphere, primarily the ionosphere. Inversion of the observed Doppler data yields vertical profiles of the Martian refractivity and electron density. The electron density profiles show the presence of two layers with peak densities and peak heights that are consistent with empirical model results. Our study demonstrates the feasibility and future potential of the crosslink radio occultation technique in the exploration of planetary atmospheres.

Solar cycle variations in the ionosphere of Mars as seen by multiple Mars Express data sets

“…Therefore, any comparison should be treated like profiles with transition characteristics between both periods. As observed in Ao et al [], the secondary layer totally disappeared in one of the profiles (the one which has a more reduced topside).…”

“…Despite the limited observations, the analysis of the TEC daily evolution in Figure and the pressure relationship between dynamic solar wind pressure and maximum thermal pressure (calculated from AIS data set) in Figure show that this scenario is totally realistic and consistent with MaRS, as the predicted TEC by the model and the MARSIS subsurface observations agree with this hypothesis. Additionally, this is somehow confirmed by the recent work carried out by Ao et al [], which has provided the first demonstration of cross‐link occultation density profiles between two different spacecraft, the first time that this happens at a planet other than Earth. The series of three cross‐link occultation experiments were acquired between the Mars Odyssey and Mars Reconnaissance Orbiter spacecraft in September 2007 with solar zenith angles between 40 and 53°, much lower than the ones that we show in this study.…”

Mars' Ionospheric Interaction With Comet C/2013 A1 Siding Spring's Coma at Their Closest Approach as Seen by Mars Express

“…Similar to the local plasma density, the topside ionosphere also has a variable behavior. NeMars is ideal for comparisons with these electron density profile observations, as previously demonstrated by other studies such as in support of in situ Mars crosslink radio-occultations (Ao et al, 2015), solar cycle variations in the Martian ionosphere , annual and solar cycle TEC behavior (Cartacci et al, 2018;, and ionospheric removal for radar surface studies (Ilyushin et al, 2017). NeMars is an empirical model that describes the electron density distribution with altitude in Mars' ionosphere with respect to SZA, solar activity, and heliocentric distance.…”

Reply to comment by Pätzold et al. on “Mars Express radio‐occultation data: A novel analysis approach”

“…The motivation for developing a new approach was the fact that many soundings of the Martian environment using the radio-occultation technique correspond to regions located near the twilight terminator of the planet. In these regions, the ionosphere does not exhibit spherical symmetry, and applying the radio science inversion method is therefore questionable [see, e.g., Ao et al, 2015]. The method we present in Grandin et al [2014] precisely avoids making the assumption of spherical symmetry for the ionosphere, which is why our final aim will be to reach a version of the model allowing to analyze a great number of profiles.…”

“…The reproach regarding the use of the expression "Doppler shift," in the beginning of the section titled "The 'novel approach' and where it fails, step by step," is unfounded. We simply invite the authors of the Comment to read more carefully the second paragraph of section 1 in Grandin et al [2014]; they will see that our definition of the frequency residuals is essentially the same as in Ao et al [2015].…”