Mars Reconnaissance Orbiter Mission Research Articles

Range resolution enhancement of SHAllow RADar (SHARAD) data via bandwidth extrapolation technique: Enabling new features detection and improving geophysical investigation

The SHAllow RADar (SHARAD) is a subsurface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument for NASA's Mars Reconnaissance Orbiter (MRO) mission, the second longest-lived mission to orbit Mars after Mars Odyssey. Developed by an Italian-US Team, SHARAD was designed to investigate to depth of up to one kilometer in the Martian subsurface and to map dielectric discontinuities associated with compositional and/or structural changes. The radar mapping began in November 2006 and, after 16 years of operations, SHARAD has mapped most of the planet's surface (∼55%), contributing a data volume for the entire MRO mission that exceeds that of all the past Mars missions combined.Designed to complement the lower-frequency, relatively narrower bandwidth capability of the MARSIS sounding radar, SHARAD emits an 85μs, frequency-modulated (10 MHz) chirp at a central frequency of 20 MHz to increase the signal-to-noise ratio (SNR) and achieve a finer resolution compared to MARSIS. On the ground, echoes recorded by the radar are range compressed using conventional pulse compression techniques yielding a nominal range resolution of 15 m (vacuum, 5–8 m in typical Martian materials). Additionally, synthetic aperture processing is performed in along-track to increase the resolution up to 300–500 m.Throughout the entire mission duration, SHARAD provided a diverse and extensive range of imaging data. It was able to observe the internal structures of Planum Boreum and Planum Australe, two icy deposits that contain the North and South Polar Layered Deposits (NPLD-SPLD), thought to contain valuable information about the planet's past climate. The radar unveiled the massive deposits of buried CO2 ice below the southern residual ice cap (SRIC), which confirmed the influence of the planet obliquity and insolation in the accumulation of dry ice. Furthermore, it revealed the intricate lava flows structures in the Tharsis Volcanic region, suggesting that the planet experienced deposition by multiple volcanic episodes.However, radar resolution often poses a limitation for subsurface investigations in many regions. Only recently, processing techniques have focused on enhancing SHARAD radargrams vertical resolution by implementing the Bandwidth Extrapolation (BWE) technique. This approach has demonstrated an improvement of the vertical resolution while preserving the time-of-arrival (TOA) and amplitude of the detected echoes. The resulting super-resolved data products exhibit better separation between radar returns, thus improving the overall understanding of the investigated terrains. The obtained results demonstrate the value of implementing the BWE techniques in the data processing pipeline whenever radar sounders are involved.

PSUP: A Planetary SUrface Portal

The large size and complexity of planetary data acquired by spacecraft during the last two decades create a demand within the planetary community for access to the archives of raw and high level data and for the tools necessary to analyze these data. Among the different targets of the Solar System, Mars is unique as the combined datasets from the Viking, Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter missions provide a tremendous wealth of information that can be used to study the surface of Mars. The number and the size of the datasets require an information system to process, manage and distribute data. The Observatories of Paris Sud (OSUPS) and Lyon (OSUL) have developed a portal, called PSUP (Planetary SUrface Portal), for providing users with efficient and easy access to data products dedicated to the Martian surface. The objectives of the portal are: 1) to allow processing and downloading of data via a specific application called MarsSI (Martian surface data processing Information System); 2) to provide the visualization and merging of high level (image, spectral, and topographic) products and catalogs via a web-based user interface (MarsVisu), and 3) to distribute some of these specific high level data with an emphasis on products issued by the science teams of OSUPS and OSUL. As the MarsSI service is extensively described in a companion paper (Quantin-Nataf et al., companion paper, submitted to this special issue), the present paper focus on the general architecture and the functionalities of the web-based user interface MarsVisu. This service provides access to many data products for Mars: albedo, mineral and thermal inertia global maps from spectrometers; mosaics from imagers; image footprints and rasters from the MarsSI tool; high level specific products (defined as catalogs or vectors). MarsVisu can be used to quickly assess the visualized processed data and maps as well as identify areas that have not been mapped yet. It also allows overlapping of these data products on a virtual Martian globe, which can be difficult to use collectively. The architecture of PSUP data management layer and visualization is based on SITools2 (Malapert and Marseille, 2012) and MIZAR (Module for Interactive visualiZation from Astronomical Repositories) respectively, two CNES generic tools developed by a joint effort between the French space agency (CNES) and French scientific laboratories. Future developments include the addition of high level products of Mars (regional geological maps, new global compositional maps…) and tools (spectra extraction from hyperspectral cubes). Ultimately, PSUP will be adapted to other planetary surfaces and space missions in which the French research institutes are involved.

IDENTIFYING SURFACE CHANGES ON HRSC IMAGES OF THE MARS SOUTH POLAR RESIDUAL CAP (SPRC)

Abstract. The surface of Mars has been an object of interest for planetary research since the launch of Mariner 4 in 1964. Since then different cameras such as the Viking Visual Imaging Subsystem (VIS), Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), and Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) have been imaging its surface at ever higher resolution. The High Resolution Stereo Camera (HRSC) on board of the European Space Agency (ESA) Mars Express, has been imaging the Martian surface, since 25th December 2003 until the present-day. HRSC has covered 100 % of the surface of Mars, about 70 % of the surface with panchromatic images at 10-20 m/pixel, and about 98 % at better than 100 m/pixel (Neukum et. al., 2004), including the polar regions of Mars. The Mars polar regions have been studied intensively recently by analysing images taken by the Mars Express and MRO missions (Plaut et al., 2007). The South Polar Residual Cap (SPRC) does not change very much in volume overall but there are numerous examples of dynamic phenomena associated with seasonal changes in the atmosphere. In particular, we can examine the time variation of layers of solid carbon dioxide and water ice with dust deposition (Bibring, 2004), spider-like channels (Piqueux et al., 2003) and so-called Swiss Cheese Terrain (Titus et al., 2004). Because of seasonal changes each Martian year, due to the sublimation and deposition of water and CO2 ice on the Martian south polar region, clearly identifiable surface changes occur in otherwise permanently icy region. In this research, good quality HRSC images of the Mars South Polar region are processed based on previous identification as the optimal coverage of clear surfaces (Campbell et al., 2015). HRSC images of the Martian South Pole are categorized in terms of quality, time, and location to find overlapping areas, processed into high quality Digital Terrain Models (DTMs) and Orthorectified Images (ORIs) and projected into polar stereographic projection using DLR (Deutsches Zentrum für Luft- und Raumfahrt; German Aerospace Center)’s VICAR and GIS software with modifications developed by Kim & Muller (2009). Surface changes are identified in the Mars SPRC region and analysed based on their appearance in the HRSC images.

Mars to Earth communications through orbiters: Delay‐Tolerant/Disruption‐Tolerant Networking performance analysis

SUMMARYDelay‐Tolerant/Disruption‐Tolerant Networking (DTN) architecture will be used in future deep space missions, to enable autonomous networking operations and disruption‐tolerant data communications. Therefore, it is worth analyzing the performance of the DTN Bundle Protocol (BP) in a realistic deep space environment, reproducing the characteristics of Mars missions. After a comprehensive introduction on data communications between Mars and Earth, the paper presents the essential features of both the BP DTN architecture and the Licklider Transmission Protocol (LTP), adopted here as BP convergence layer on deep space links, thanks to its ability to cope with the very long delays typical of this environment. The focus of our experiments is on analysis of the bundle flow from a Mars lander to an Earth control center through an intermediate relay node, for which two configurations are considered, inspired to Odyssey and Mars Reconnaissance Orbiter missions, respectively. Results are obtained by means of a test bed consisting of some GNU/Linux personal computers running either Interplanetary Overlay Network (ION) or DTN2 BP implementations. The analysis of results aims to highlight the role played by BP and LTP in tackling the challenges of Mars to Earth communications. Copyright © 2013 John Wiley & Sons, Ltd.

The SHAllow RADar (SHARAD) Onboard the NASA MRO Mission

This paper describes the mission concepts, design, and achievements of the Italian Space Agency (ASI)-provided Mars SHAllow RADar (SHARAD) sounder high-frequency (HF) sounding radar, used onboard the National Aeronautics and Space Administration (NASA) Mars Reconnaissance Orbiter (MRO) Spacecraft. Its goals are the detection of liquid or solid water below the surface, and the mapping of subsurface geologic structures. Following a brief overview of the MRO mission and of its main science objectives, the paper introduces the basic principles of operation of the radar sounder, and addresses the major design issues faced by such a system. The greatest challenges faced in the design are the control of the interference from off-nadir echoes and the need for a high signal fidelity over a very large fractional bandwidth. The core of the paper is devoted to describing how the above problems have been tackled in the design of the SHARAD instrument, and the main characteristics of its architecture. The two key features of the instrument system design are 1) generation of the transmitted signal directly at the transmitted frequency; and 2) sampling performed directly at the radio frequency (by means of a subsampling technique). The careful design of these features, intended to keep the analog signal path very simple, minimizes distortions and stability problems. An overview of the calibration approach of both the system impulse response and the antenna gain at nadir versus solar array position, an assessment of the in-flight performance of the instrument, and a short summary of the achieved science results are also provided.

Stratigraphy, mineralogy, and origin of layered deposits inside Terby crater, Mars

The 174 km diameter Terby impact crater (28.0°S–74.1°E) located on the northern rim of the Hellas basin displays anomalous inner morphology, including a flat floor and light-toned layered deposits. An analysis of these deposits was performed using multiple datasets from Mars Global Surveyor, Mars Odyssey, Mars Express and Mars Reconnaissance Orbiter missions, with visible images for interpretation, near-infrared data for mineralogical mapping, and topography for geometry. The geometry of layered deposits was consistent with that of sediments that settled mainly in a sub-aqueous environment, during the Noachian period as determined by crater counts. To the north, the thickest sediments displayed sequences for fan deltas, as identified by 100 m to 1 km long clinoforms, as defined by horizontal beds passing to foreset beds dipping by 6–10° toward the center of the Terby crater. The identification of distinct sub-aqueous fan sequences, separated by unconformities and local wedges, showed the accumulation of sediments from prograding/onlapping depositional sequences, due to lake level and sediment supply variations. The mineralogy of several layers with hydrated minerals, including Fe/Mg phyllosilicates, supports this type of sedimentary environment. The volume of fan sediments was estimated as >5000 km 3 (a large amount considering classical martian fan deltas such as Eberswalde (6 km 3)) and requires sustained liquid water activity. Such a large sedimentary deposition in Terby crater is characteristic of the Noachian/Phyllosian period during which the environment favored the formation of phyllosilicates. The latter were detected by spectral data in the layered deposits of Terby crater in three distinct layer sequences. During the Hesperian period, the sediments experienced strong erosion, possibly enhanced by more acidic conditions, forming the current morphology with three mesas and closed depressions. Small fluvial valleys and alluvial fans formed subsequently, attesting to late fluvial processes dated as late Early to early Late Hesperian. After this late fluvial episode, the Terby impact crater was submitted to aeolian processes and permanent cold conditions with viscous flow features. Therefore, the Terby crater displays, in a single location, geologic features that characterize the three main periods of time on Mars, with the presence of one of the thickest sub-aqueous fan deposits reported on Mars. The filling of Terby impact crater is thus one potential “reference geologic cross-section” for Mars stratigraphy.

Atmospheric Modeling Using Accelerometer Data DuringMars Reconnaissance Orbiter Aerobraking Operations

Aerobraking as an enabling technology for the Mars Reconnaissance Orbiter mission was used in numerous analyses based on various data types to maintain the aerobraking time line. Among these data types were measurements from spacecraft accelerometers. This paper reports on the use of accelerometer data for determining atmospheric density during Mars Reconnaissance Orbiter aerobraking operations. Acceleration was measured alongthreeorthogonalaxes,althoughonlydatafromthecomponentalongtheaxisnominallyintothe flowwereused during operations. For a 1-s count time, the root-mean-square noise level was 0:004 mm=s 2 , permitting density recovery to 0:008 kg=km 3 , or about 0.023% of the mean density at periapsis, during aerobraking. Accelerometer data were analyzed in near real time to provide estimates of density, density scale height, orbit-to-orbit variability, latitudinal-seasonalvariations,longitudinalwaves,andotherphenomenainthethermosphere.Summariesaregiven of the aerobraking phase of the mission, the accelerometer data analysis methods and operational procedures, some applications to determining thermospheric properties, correlation with the Mars Global Surveyor and Odyssey missions, and some remaining issues on interpretation of the data.

Aeroheating Analysis for the Mars Reconnaissance Orbiter with Comparison to Flight Data

The aeroheating environment of the Mars Reconnaissance Orbiter (MRO) has been analyzed using the direct simulation Monte Carlo and free-molecular techniques. The results of these analyses were used to develop an aeroheating database to be used for the preflight planning and the in-flight operations support for the aerobraking phase of the MRO mission. The aeroheating predictions calculated for the MRO include the heat transfer coefficient (CH) over a range of angles-of-attack, sideslip angles, and number densities. The effects of flow chemistry, surface temperature, and surface grid resolution were also investigated to determine the aeroheating database uncertainties. Flight heat flux data has been calculated from surface temperature sensor data returned to Earth from the MRO in orbit around Mars during the aerobraking phase of its mission. The heat flux data have been compared to the aeroheating database and agree favorably.

Water, Water, Not Everywhere?

![Figure][1] CREDIT: ZUBER ET AL. The story of water on Mars has a checkered past. Historically thought to be criss-crossed by alien canals, the arrival of the first spacecraft showed that the red planet is bone dry. A flotilla of satellites has since traveled to Mars. Water ice has been seen dusting the ground, in hydrous minerals, in glaciers draped on volcano walls, and, the vast majority, locked up in the polar caps. Such a frosting gives a clue that water was once abundant on Mars and the planet's early climate was wet. Since then, water has been lost from the surface and atmosphere. It is possible that some may have survived underground, occasionally seeping to the surface, and so signs of flowing water have been sought extensively. Such places would be top destinations for future landers to search for signs of extant or past life. The primary mission of the latest spacecraft to reach the red planet, the Mars Reconnaissance Orbiter (MRO), is to study its hydrologic history. It is opening up new vistas with its exceptionally keen eyesight. Regional landforms were mapped before, but MRO can now spot boulders less than a few meters in size, allowing Martian global geology to be surveyed on a human scale over vast areas. Among several other instruments, it also contains a radar sounder for exploring subsurface ice deposits and is accurately measuring Mars' gravity. This special issue presents scientific results from MRO detailed images of the ice-capped poles and regions thought to have been shaped by liquid water, both recently and in the past. The papers in this issue show that evidence for liquid water is rare and difficult to discern (see also the News story by Kerr, p. [1673][2]). Images of supposed ancient ocean floors and riverbeds show no obvious signs that liquid water was ever present. Reexamination of some landforms implies that they have been formed by flowing lava, not water. The only locations where features seem to indicate the presence of liquid water today or in the recent past are on the rims of craters and some gullies, suggesting that heat from impacts may have been the trigger for trickles rather than a revealed water table. Radar and gravity data show that the cap on Mars' south pole now holds the largest reservoir of relatively pure water ice on the planet, and layers there and in the north polar cap reveal seasonal oscillations in climate. These papers thus provide a tour around the martian world of water in the first 100 days or so of the main MRO mission. More will be revealed as it continues to probe the surface, including Mars' mineralogy, and focuses several instruments on its atmosphere, dust, and clouds. But there is a lot to drink already. [1]: pending:yes [2]: /lookup/doi/10.1126/science.317.5845.1673

SHARAD sounding radar on the Mars Reconnaissance Orbiter

SHARAD (SHAllow RADar) is a sounding radar provided by Agenzia Spaziale Italiana (ASI) as a Facility Instrument on the Mars Reconnaissance Orbiter mission. Its 20‐MHz center frequency and 10‐MHz bandwidth complement the lower‐frequency, relatively narrower bandwidth capability of the MARSIS sounding radar. A joint Italian‐U.S. team has guided the experiment development and is responsible for data analysis and interpretation. The radar transmits signals at a 700 Hz pulse repetition frequency (PRF) and collects reflections from both the surface and near subsurface of Mars. Vertical and horizontal resolutions are, respectively, 15 m (free‐space) and 3–6 km (cross‐track) by 0.3–1 km (along‐track). The scientific objective of SHARAD is to map, in selected locales, dielectric interfaces to at least several hundred meters depth in the Martian subsurface and to interpret these results in terms of the occurrence and distribution of expected materials, including competent rock, soil, water, and ice. A signal‐to‐noise ratio of ∼50 dB (for a specular surface return) is achieved with 10 W of radiated power by using range and azimuth focusing in ground data processing. Preprocessed data as well as range‐ and azimuth‐focused data will be formatted according to Planetary Data System (PDS) standards and be made available from the ASI Science Data Center (ASDC) and from the Geosciences Node of the Planetary Data System (PDS). Important targets for SHARAD include the polar layered deposits, sedimentary stacks (especially in Terra Meridiani), buried channel systems, buried impact craters, volcanic complexes, and shallow ice deposits in equilibrium with the atmosphere.