Rolando L. Jordan

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS): concept and performance

Describes the key features and expected performance of a new radar sounder instrument currently under development by a team of Italian and US researchers and industrial partners, selected to fly with the ESA Mars Express orbiter scheduled for launch to Mars late in 2003. Very low transmitted frequency (1-5 MHz), large instantaneous bandwidth and coherent on-board processing techniques will make it possible to acquire a large amount of science-relevant data about the Mars interior, surface and atmosphere ensuring global coverage at all latitudes while respecting the Mars Express mission constraints.

Shuttle radar topography mapper (SRTM)

The use of interferometric SAR (IFSAR) to measure elevation is one of the most powerful and promising capabilities of radar. A properly equipped spaceborne IFSAR system can produce a highly accurate global digital elevation map, including cloud-covered areas, in significantly less time and at significantly lower cost than with other systems. For accurate topography, the interferometric measurements must be performed simultaneously in physically sperate receive system, since measurements made at different times with the same system suffer significant decorrelation. The US/German/Italian spaceborne imaging radar C/X-band SAR (SIR-C/X-SAR), successfully flown twice in 1994 aboard the Space Shuttle Endeavor, offers a unique opportunity for global multifrequency elevation mapping by the year 2000. With appropriate augmentation, SIR-C/X-SAR is capable of producing an accurate elevation map covering 80 percent of the Earths land surface in a single 10-day Shuttle flight. The existing US SIR-C SCANSAR mode provides a 225-km swath at C-band, which makes this coverage possible. Addition of a C-band receive antenna, extended from the Shuttle bay on a mast and operating in concert with the existing SIR-C antenna, produces an interferometric pair. Accuracy is enhanced by utilizing the SIR-C dual polarizations simultaneously to form separate SCANSAR beams. Due to the practical limitation of approximately 60 meters for the mast length, the longer SIR-C L-band wavelength does not produce useful elevation measurement accuracy. IFSAR measurements can also be obtained by the German/Italian X-SAR, simultaneously with SIR-C, by utilizing an added outboard antenna at X-band to produce a swath coverage of about 50 km. Accuracy can be enhanced at both frequencies by processing both ascending and descending data takes. It is estimated that the 90 percent linear absolute elevation error achievable is less that 16 meters for elevation postings of 30 meters. This will be the first use of spaceborne IFSAR to acquire accurate topographic data on a global scale.

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS): subsurface performances evaluation

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 pot-lions of the crust of Mars. Three secondary objectives are also defined subsurface geologic probing, surface characterization, and ionosphere sounding. In order to obtain the primary objectives the Radar Sounder design was based on the Ice/water interface and Dry/ice interface scenario: defining the material composition of the first layers and porosity and the pore filling materials. Concerning the surface, we have characterized the geometric structure in terms of a large-scale morphology, on which a small-scale geometric structure, due to rocks, is superimposed, taking into account also that recently the structure of the planets surface was described by means of fractals and in particular the new MARS surface models obtained by processing of the MOLA data. According to these models, this paper provides a description of the operational planning approach and expected performances of MARSIS.

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.

Future NASA spaceborne SAR missions

Two Earth-orbiting radar missions are planned by NASA-Shuttle Radar Topography Mission (SRTM) and LightSAR. The SRTM will fly aboard the Shuttle using interferometric synthetic aperture radar (IFSAR) to provide a global digital elevation map. SRTM is jointly sponsored by NASA and the National Imagery and Mapping Agency (NIMA). The LightSAR will utilize emerging technology to reduce mass and life-cycle costs for a mission to acquire SAR data for Earth science and civilian applications and to establish commercial utility. LightSAR is sponsored by NASA and industry partners. The use of IFSAR to measure elevation is one of the most powerful and practical applications of radar. A properly equipped spaceborne IFSAR system can produce a highly accurate global digital elevation map, including cloud-covered areas, in significantly less time and at significantly lower cost than other systems. For accurate topography over a large area, the interferometric measurements can be performed simultaneously in physically separate receive systems. The Spaceborne Imaging Radar C (SIR-C), successfully flown twice in 1994 aboard the Space Shuttle Endeavour, offers a unique opportunity for global multifrequency elevation mapping by the year 2000. The addition of a C-band receive antenna of approximately 60 m length, extended from the Shuttle bay on a mast, and operating in concert with the existing SIR-C antenna, produces an interferometric pair. It is estimated that the 90 percent linear absolute elevation error achievable is less that 16 meters for elevation postings of 30 meters. The SRTM will be the first single-pass spaceborne IFSAR instrument and will produce a near-global high-resolution digital topography data set.

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.

Coherent cancellation of surface clutter for radar sounding

Considers the cancellation of surface clutter returns from the composite surface/subsurface signal received by a low frequency nadir looking pulsed radar sounder. The two considered techniques are Doppler filtering for along track clutter cancellation and dual-antenna processing for cross track clutter cancellation. The improvement factor due to the application of the cancellation techniques is derived as a function of various operative parameters.

MARSIS experiment: design and operations overview

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a radio frequency subsurface radar sounder designed to operate on the international Mars Express mission, an ESA program for the orbital and in-situ study of the subsurface, surface, ionosphere and atmosphere of the planet Mars. The Mars Express Orbiter spacecraft is developed operated and fully funded by ESA with the exception of the seven payload scientific instruments which will be used for remote observation of the red planet. According to the current ASI/NASA agreement the MARSIS instrument has an Italian PI, an U.S. Co-PI, and Co-Is from the Italy, the U.S. and other countries. There is also an U.S. Experiment Manager and an Italian Deputy Experiment Manager.

Design of shuttle radar topography mapper (SRTM)

A radar interferometric topography mapper designed to acquire digital elevation maps of the earths surface from the Space Shuttle is described and its performance estimated. The system described is capable of acquiring a topographic map of all of the earth between 54 degree(s)S and 60 degree(s)N latitude to a height accuracy of 16 meters absolute. This planned mission will be the first use of radar interferometry to acquire topographic data on a global scale, the data of which will have significant impact of many applications. The system uses the previously flown SIR- C C-Band synthetic aperture radar system augmented by a second interferometric antenna deployed 60 meters from the Shuttle. The operation of the system, which requires the simultaneous use of dual polarization radars operating with horizontal and vertical polarizations with electronic beam scanning, is described. Performance parameters which drive the vertical height accuracy of this system and the implementation of solutions necessary to meet the performance objectives are described.

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.