International audienceThe martian subsurface has been probed to kilometer depths by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument aboard the Mars Express orbiter. Signals penetrate the polar layered deposits, probably imaging the base of the deposits. Data from the northern lowlands of Chryse Planitia have revealed a shallowly buried quasi-circular structure about 250 kilometers in diameter that is interpreted to be an impact basin. In addition, a planar reflector associated with the basin structure may indicate the presence of a low-loss deposit that is more than 1 kilometer thick
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
Spaceborne X-band synthetic aperture radars (SARs) represent a well-established tool for Earth remote sensing at very high spatial resolution (order of meters). Until now, SAR has not been exploited for hydrological cycle modelling and numerical weather forecast, however, there are scientific evidences that at X band and beyond: i) atmospheric precipitation in liquid and ice phase affect SAR imagery and its intensity can be retrieved, ii) snow areal extent and mass (water-equivalent) can be detected and estimated. KydroSAT mission concept foresees a miniaturised fully-digital SAR at Ku and Ka band (KydroSAR), specifically devoted to detecting and estimating atmospheric precipitation and surface snow; its baseline includes dual-polarization capability, high orbit duty cycle (>75%), flexible ground resolution (5-150 m), and a large variable swath (50-150 km), doubled with formation of two minisatellites both carrying a KydroSAR. Moreover, the mission concept foresees the along-track convoy with the COSMO-SkyMed and SAOCOM SAR platforms, allowing the observation of the same scene at L, X, Ku and Ka bands. The challenging requirements of this architecture require the development of new technologies such as Digital Beam Forming and Direct Digital to RF Conversion. In order to exploit the synergic approach of the KydroSAT convoy for precipitation, in this work we will simulate and discuss the SAR response at X, Ku and Ka bands of the same scene, using the SAR forward model described in Mori et al. (2017). Subsequently, an example retrieval of Snow Equivalent Water (SWE) by Ku-SAR will be given
The MARSIS observations are optimized during periods when the pericenter of the orbit is near or below zero degrees sun elevation ("nightside") 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.
AThe NIARSIS primary scientific objectives are to map the distribution ofwater, both liquid and solid, in the upper portions of the crust of Mars. Detection of such reservoirs of water will address key issues in the hydrologic, geologic, climatic and possible biologic evolution of Mars, including the current and past global inventory of water, mechanisms of transport and storage of water.Three secondary objectives are defined for the MARSIS experiment: subsurface geologic probing, surface characterization, and ionosphere sounding. According to the previous scientific objectives, this paper provides a description of the design approach, expected performances and first science results of the MARSIS. In order to assess the performances, taking into account of Mars Orbital Laser Altimeter (MOLA) data, some models, either dielectric and geometric, of the Martian crust have been worked out, being the related structure the result of many different processes and validate by the preliminary results. Moreover the two most likely scenarios representing the relevant interfaces MARSIS are: Icelwater(IIW) interface -in this scenario the pores are filled with ice from the surface down to a depth below which liquid water is stable and becomes the pore-filling material. Drylice(DII) interface -here the pore-filling material is considered to be gas or some other vacuum-equivalent material up to a depth, below which ice fills the pores. Hence the interface to detect is between dry regolith and ice-filled regolith. Taking into account the previous models, the MARSIS instrument was designed as a lowfrequency nadir-looking pulse limited radar sounder and altimeter with ground penetration capabilities of the order of some kilometers; this radar can be effectively operated at any altitude lower than 800 km. Moreover several factors that can strongly reduce the subsurface detection dynamic mainly the noise and the surface clutter. Three techniques are used to increase the detection performance against surface clutter: Doppler beam sharpening: the Doppler azimuth processing significantly reduces the surface echoes coming from along track off nadir reflections. A secondary monopole antenna, oriented along the nadir axis will receive the off-nadir surface returns, that could be thus subtracted by the primary antenna composite signal, further reducing the surface clutter level . Finally, the Marsis frequency-agile design will allow to tune the sounding parameters in response to changes in sun illumination condition, latitude etc.. The best penetration capabilities will be obtained during night side observation, when also the longest wavelengths can be operated. The multi frequency observation will allow the estimation of the material attenuation in the crust and will give significant indications on the dielectric properties of the detected interfaces. Finally echo profiles collected at two different frequencies can be processed to separate the subsurface reflections, which are strongly dependent on the frequency, from the surface reflections...
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