A. Masdea

MARSIS data inversion approach: Preliminary results

An approach to the inversion of the data available from the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on Mars Express is described. The data inversion gives an estimation of the materials composing the different detected interfaces, including the impurity (inclusion) of the first layer, if any, and its percentage, by the evaluation of the values of the permittivity that would generate the observed radio echoes. The data inversion method is based on the analysis of the surface to subsurface power ratio and the relative time delay as measured by MARSIS. The constraints, due to the known geological history of the surface, the local temperature and the thermal condition of the observed zones and the results of other instruments on Mars Express and other missions to Mars, have to be considered to improve the validity of the utilized models and the obtained results that are given in parametric way.

MARSIS Data Inversion Approach

In this paper we describe an inversion approach in order to analyze data from the MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) instrument on Mars Express. The inversion process allows the dielectric constant of the subsurface material to be estimated provided the dielectric constant of the surface is known. In addition, if impurity are present, it is possible to estimate the dielectric constant of any inclusions as well as the percentage amount of material in the inclusions relative to the host material provided knowledge of the host material up to the depth where the interface has been detected is available. The data inversion method is based on the analysis of the surface to subsurface power ratio and the relative time delay as measured by MARSIS. The data inversion has been performed at several frequencies in order to estimate the frequency dependent parameters affecting the behavior of the radar echoes. It is necessary that the surface and subsurface interfaces have the same roughness in order to estimate the Subsurface Fresnel reflectivity. As a preliminary approach, only flat surface have been selected. MOLA (Mars Orbiter Laser Altimeter) has already provided detailed data on the visible Martian surface and a simulator, with a facet model, has been utilized to use MOLA data in order to verify the correct selection of the frames that will be used for the data inversion (absence of clutter echoes).

Mars ionosphere data inversion by MARSIS surface and subsurface signals analysis

According to the Mars Express mission , the MARSIS primary scientific objectives are to map the distribution of water, both liquid and solid, in the upper portions of the crust of Mars. Moreover three secondary objectives are defined for the MARSIS experiment: subsurface geologic probing, surface characterization, and ionosphere sounding.

Ionosphere compensation and stepped frequency processing in the MARSIS experiment

This paper is addressed to the improvement of the range resolution of MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) by means of a modified version of the stepped frequency processing algorithm. MARSIS is a low frequency, pulse-limited radar sounder and altimeter selected by ESA as a payload of the Mars Express mission. The ionosphere affects MARSIS operation in terms of phase distortion, attenuation and Faraday rotation. The ionosphere fine compensation is obtained according to the uniform model, allowing, with the correctly compensated data, the production of MARSIS images at higher resolution. In this way it is possible to detect hidden interfaces never seen before due to MARSIS coarse vertical resolution.

Doppler analysis for data inversion and image processing in the MARSIS experiment

This paper is addressed to MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) signal analysis. The effect of tilted layers, detected within different Doppler filters, is taken into account in order to improve the quality and the quantity of the data set needed to perform the data inversion, that is the estimation of the dielectric constant of the materials composing the different detected interfaces.

Weighting network influence on the geometric term correction in MARSIS data inversion

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a low frequency, pulse-limited radar sounder and altimeter selected by ESA as a payload of the Mars Express mission. This work retraces the processing that leads to the extraction of parameters needed to perform the data inversion pointing out an effect caused by the weighting network application in presence of volume scattering that could jeopardize the backscattering-related geometry interpretation on a specific set of data.

Shallow Radar (SHARAD) investigations over Sinus Meridiani

Mars equatorial region Sinus Meridiani has been investigated by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor (MGS) revealing the presence of gray hematite. Laboratory measurements on magnetic minerals including gray hematite have been performed afterwards suggesting that the Shallow Radar (SHARAD) instrument onboard the Mars Reconnaissance Orbiter (MRO) should be capable to reveal the reflectivity contrast, the influence on the penetration depth and the temperature dependence effect on the received echoes. The proposed wok suggests a possible study aimed to evaluate such considerations including both theoretical models as well as experimental data analysis.

Range compression optimization for subsurface investigation in the MARSIS experiment

This work deals with the range compression applied to MARSIS (Mars Radar for Subsurface and Ionosphere Sounding) data proposing a new approach to improve the S/N after matched filtering for both surface and subsurface responses. It will be also illustrated how the geometric term correction can be performed on a particular class of data previously not correctable according to surface/subsurface theoretical models. Finally, it will be demonstrated how a better estimation of the volume scattering can be obtained.

Subsurface sounding in Northern hemisphere for Mars by MARSIS: Mars express mission

The MARSIS observations are optimized during periods when the pericenter of the orbit is near or below zero degrees sun elevation (ldquonightsiderdquo) and the nightside phase, the last of the primary MEX mission, occurs on March-July 2005, in the northern latitude of MARS regions. This paper provides a description of the modeling approach and of the expected performance of the MARSIS radar in the northern hemisphere of Mars. Few models, suitable for a preliminary analysis of the MARSIS instruments are reported. The knowledge of these performance, evaluated according to the model used for the surface and subsurface of the Martian crust, are necessary in order to decide, during the planning activity of the mission, the radar operative mode. In addition the model utilized are an effective tool for the simulator that has to perform the radar equation inversion in order to evaluate, by the radar returns, the surface and subsurface dielectric characteristics. Few simulation results of the surface characteristics are reported and a radar gram is shown, as an example, in order to state the preliminary criteria for the radar equation inversion.

Subsurface Investigations by MARSIS in Mars Express Mission

The analysis of the surface return echoes in the subsurface data extraction in North Mars Polar region has shown the possibility to utilize simplified surface models, at least, for the purpose of the evaluation of the penetration depth capability. The surface simulation, obtained starting from MOLA data, has been utilized during the planning activity in order to select the MARSIS operative sequence in order to optimize the amount of scientific data taking into account the data rate available and the scientific target to be investigated during the next part of the mission. Moreover a simulator, still in progress, utilizing the surface characteristics will perform the analysis of the real data in order to make available the required information expected, by the mission, in terms of detection and identification of dielectric constant on the surface and subsurface.