JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, E05S05, doi:10.1029/2006JE002745, 2007 Click Here tor Full Article SHARAD sounding radar on the Mars Reconnaissance Orbiter Roberto Seu,' Roger J. Phillips,^ Daniela Biccari/ Roberto Orosei,^ Arturo Masdea/ Giovanni Picardi/ Ali Safaeinili,"* Bruce A. Campbell,^ Jeffrey J. Plaut,"* Lucia Marinangeli,^ Suzanne E. Smrekar,"* and Daniel C. Nunes^ Received 7 May 2006; revised 22 September 2006; accepted 19 October 2006; published 18 May 2007. [i] 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. Citation: Seu, R., et al. (2007), SHARAD sounding radar on the Mars Reconnaissance Orbiter, J. Geophys. Res., 112, E05S05, doi: 10.1029/2006JE002745. 1. Introduction ciated with water-deposited sedimentary rocks, volcanic 1.1. Experiment Overview sequences, and the seasonal and long-term obliquity-driven r n c 1 •• ji- uv J u u *i, tA/r movement ofvolatiles. Orbital remote Sensing that orobes to m Exploration from orbit and by rovers shows that Mars , ^, ^, . , ^ ^ ,,-, rr ^ , , , , ^- . ö • -i 1-4. J 1 • depths oí hundreds ot meters to kilometers oiiers the only has undergone dramatic shifts in its climate and geologic ^ . , ^ , . , , • , .• rx,, ,• ^ . {• iu • Ti. practical means tor studying such layenng over large areas, regime over time. The most important oi these is the ^. _ _, . •' ° .-' • ,, , . •.• f 1, Í u J * Í t a Í3l Electromagnetic remote sensing typically probes to transition irom an epoch oi abundant suriace water after '- ^ , , • ,•,•..•• ,, A fu u u A *t uj • * greater depths in a target medium as the illuminating the end oi heavy bombardment to a cold, dry environment. ° , / . ,^° , , _, ° In this transition, much of the surface water was trapped as ^^^elength mercases (frequency decreases). To penetrate , • 1 1 J J i J V • typical near-suriace crustal materials and characterize layers polar caps, circum-polar layered deposits, and extensive ••£-,,,,• ,• -, , A • TU A e I. • 1 • i A 1 • at sigmiicant depth, the active signal must have a wave- ground ice. The record ot changing climate and geologic , , ^ . , T^ ,• , / , x J • ., ? jr 1 • length 01 several meters or more. Radio echo (radar) processes is preserved m the subsuriace as layering asso- ° ,. ^ , . • , , , , , sounding is a technique that has been shown to reveal •¡ subsurface layers when used at the surface of the Earth INFOCOM, Università di Roma "La Sapienza," Rome, Italy. ^^ An *».• rt A \ £^ • a. A i- uv 2•Department ^ I 01tTj barth ^u and J PlanetaryTil . Sciences,O • 117Washmgton u- . TTUmversity, ^ (Ground^ i i Penetrating n, r?. Radar), r fromr i i^-imaircraft, r> andi irom orbit St. Louis, Missouri, USA. around the Moon [Feeples et al., 1978]. Radar sounding at ^istituto di Astrofísica Spaziale e Fisica Cósmica, Rome, Italy frequencies of tens to a few hundred MHz has been used to ''Jet Propulsion Laboratory, California Institute of Technology, study the Subsurface characteristics of the Earth's ice sheets, Pasadena, California, USA which can be many kilometers in thickness [e.g.,/fo/í eí a/.. Center tor barth and Planetary Studies, Smithsonian Institution, oriri/r -i Washington, D. C, USA. iUUoaJ. ''IRSPS, Università G. d'Annunzio, Pescara, Italy [4] The SHARAD (SHAllow RADar) radar sounder 'Lunar and Planetary Institute, Houston, Texas, USA. provided by Agenzia Spaziale Italiana (ASI), now in orbit aboard the Mars Reconnaissance Orbiter (MRO) [Zurek and nZ^';!^'î'.i°i!Ln^..în.'î^!Î'.T.'ifn n^'^P*"^''^^^ ""'•- Smrckar, 2007], is designed to detect dielectric contrasts Ü148-ü227/u7/2üu6jiiuü2745íbü9.üu E05S05 lof 18 E05S05 SEU ET AL.: SHARAD ON MRO E05S05 Table 1. SHARAD Team Members Team Member Role/Responsibility Institution Roberto Seu Team Leader/Radar Performance and Université di Roma "La Sapienza" Data Processing Roger Phillips Deputy Team Leader/Mission Science Washington University in St. Louis Strategy and Interpretation Daniela Biccari Mission Operations Universita di Roma "La Sapienza" Roberto Orosei Data Products lASF, Istituto Nazionale di Astrofísica Ali Safaeinili Instrument Scientist Jet Propulsion Laboratory Arturo Masdea Calibration and Commissioning Universita di Roma "La Sapienza" Costanzo Federico Data fusion and GIS University of Perugia Vittorio Formisano Science Interpretation Istituto di Fisica dello Spazio Interplanetario Pierfrancesco Lombardo Science Interpretation Universita di Roma "La Sapienza" Lucia Marinangeli Mission Science Targeting; E/PO Universita d'Annunzio Giovanni Picardi Surface Cutter Models; MARSIS Universita di Roma "La Sapienza" Sebastiano B. Serpico Science Interpretation Universita di Genova Bruce Campbell Clutter Detection and Mitigation Center for Earth and Planetary Studies, Smithsonian Inst. Jeffrey Plaut MARSIS Correlation Jet Propulsion Laboratory Suzanne Smrekar Science Interpretation Jet Propulsion Laboratory associated with geologic layering on vertical scales of 15 m tributed to the community at large from the ASI Science or better and to probe to typically subkilometer depths. Data Center (ASDC) in Frascati, Italy, and from the Geo- SHARAD will complement the spatially coarse, but deep sciences Node of the Planetary Data System at Washington sounding of the MARSIS instrument on Mars Express University in St. Louis, USA (WUSTL-PDS). [Picardi et al, 2005] (see section 2.2). The SHARAD radar [7] The Italian portion of the SHARAD team was orig- emits electromagnetic (EM) waves from its 10-m dipole inally appointed by ASI, with Roberto Seu of Université di antenna, and measures the reflections from both the Martian Roma "La Sapienza" as the Team leader. Subsequently, surface and subsurface. Waves that are transmitted into the three American scientists were selected by NASA in subsurface may reflect from dielectric interfaces and return response to an AO, with Roger Phillips of Washington to the instrument at greater time delay than the surface echo. University appointed Deputy Team Leader. US Participating A two-dimensional picture (a "radargram") of the surface Scientists likely will be added to the team. The frill list of and subsurface is built up in one direction by time delay and team members is given in Table 1, and includes Ali in an orthogonal direction by motion of the MRO spacecraft Safaeinili, the Instrument Scientist at JPL. The SHARAD (S/C) along its orbit (see Figures 3, 4, and 8). The primary team provided the instrument requirements to the prime obstacle to the identification of subsurface echoes is the contractor, AAS, and closely monitored the development of interference from off-nadir surface echoes (known as "sur- the hardware to ensure that the requirements were met. face clutter") that arrive at the radar receiver with the same [s] A review of the SHARAD radar experiment with an time delay as subsurface echoes. This can be mitigated by emphasis on its design is given by Seu et al. [2004]. various methods discussed in section 8. [5] SHARAD operates with a 20-MHz center frequency 1.2. Scientific Objectives and a 10-MHz bandwidth, which translates to a vertical [9] The primary objective of the SHARAD experiment is resolution of 15 m in free-space and 151 ^Je m in a medium to map, in selected locales, dielectric interfaces to several of relative permittivity e. The transmitted signal is a 10 W, hundred meters depth in the Martian subsurface and to 85-^sec chirped (linear FM) pulse emitted from a 10-m- interpret these results in terms of the occurrence and long dipole antenna that is used for both transmitting and distribution of expected materials, including competent receiving. Horizontal surface resolution depends on surface rock, soil, water and ice [Seu et al, 2004]. This is a roughness characteristics, but for most Mars surfaces the seemingly cautious set of objectives, making no particular cross-track footprint is 3-6 km and the along-track foot- promises about the unique detection of any specific material print, narrowed by synthetic aperture processing on the (e.g., water). Nevertheless, the subsurface of Mars presents ground, is 0.3-1 km. The returned signal is recorded as a ample possibilities for dielectric contrasts. The dielectric time series of complex-valued voltages. The pulse repetition constant depends on both rock porosity and rock composi- frequency (PRF) over-samples the Doppler spectrum, tion, so boundaries between materials with differences in allowing for coherent integration of pulses on board the these properties are dielectric reflectors. This dielectric spacecraft, while still allowing for Doppler focusing in contrast could arise, for example, from sedimentary materi- ground data processing.