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SHARAD

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Schematic view of SHARAD operation onMars Reconnaissance Orbiter

SHARAD(MarsSHAllow RADar sounder) is a subsurface soundingradarembarked on theMars Reconnaissance Orbiter(MRO) probe. It complements theMARSISradar onMars Expressorbiter,[1]providing lower penetration capabilities (some hundred meters) but much finer resolution (15 metres - untapered - in free space).[citation needed]

SHARAD was developed under the responsibility of theItalian Space Agency(ASI, Agenzia Spaziale Italiana), and provided toJPLfor use on board NASA'sMars Reconnaissance Orbiterspacecraftin the frame of a NASA/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University ofSapienza University of Romeis responsible for the instrument operations, whileThales Alenia SpaceItalia (formerly Alenia Spazio) designed and built the instruments. SHARAD operations are managed by INFOCOM from the SHARAD Operation Centre (SHOC), located within theAlcatel Alenia Spacefacilities in the suburbs ofRome.

Science objectives[edit]

Radargram of north pole layered deposits from SHARAD shallow ground-penetrating radar onMars Reconnaissance Orbiter

SHARAD is intended to map the first kilometer below theMarssurface,[citation needed]providing images ofsubsurface scatteringlayers with high vertical resolution (15 m), with the intent to locate water/ice/ deposits and to map the vertical structure of the upper subsurface layers.

Characteristics[edit]

SHARAD operates on acarrier frequencyof 20 MHz, transmitting a "chirped"signal with a bandwidth of 10 MHz. Pulsewidth is 85 μs and the nominalPulse Repetition Frequencyis 700.28 Hz. Transmitted power is 10 W peak. Theantennais a 10 m dipole. Asynthetic apertureis generated on-ground to reduce the unwanted surface returns from off-nadirscatterers at the same range of the subsurface echoes.

SHARAD is physically divided into two elements:

  • the SEB (SHARAD electronic box), which contains all the electronics (instrument controller, transmitter, receiver andantennaimpedance matchingnetwork), within a metal frame which acts as thermal radiator for the electronic modules inside (Mars Reconnaissance Orbiteris an open frame spacecraft, and SHARAD has an autonomous thermal control)
  • theantenna,made by two fiber tubes, folded and stowed in a cradle (covered by thermal insulator to protect it from the heating induced by theaerobraking). Once released, the antenna extends into position thanks only to the elastic property of the material. A metal wire running inside the non-conductive tubes represents the real radiating element of the antenna. The antenna was designed and manufactured by Northrop Grumman Astro Aerospace in Carpinteria, CA.

The instrument operates at fixedPRF(700.28 Hz) and the echo is received in rank 1 (i.e., after the second transmitted pulse). Two alternate (higher and lower) PRF are available to deal with the extended mission orbit range. An open-loop tracking system, based on a priori knowledge of the surface topography, is the nominal means to position the 135 μs receive window on the expected echo position (a closed-loop tracker is available as backup).

The instrument on-boardsignal processingis minimal, and consists in a coherent presuming of the received echoes (programmable between 1 and 32 in power of 2 steps) to reduce the generated data rate, with programmable number of bits (8, 6, 4).

Thechirpsignal is generated directly on the 20 MHzcarrierby a digital chirp generator, and fed to the power amplifier, followed by a Transmit/Receive switch and thematching network. The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using anundersamplingtechnique at a rate of 26.6 MHz. A singledigital signal processorprovides both the control and processing function.

The instrument industrial team is composed as follows:

  • Instrument design, integration and test: Alcatel Alenia Space Italia (Romeplant)
  • DES (Digital electronics subsystem): Alcatel Alenia Space Italia (Milanplant - formerly Laben)
  • Chirp Generator, Receiver: Alcatel Alenia Space Italia (Rome/L'Aquilaplants)
  • Transmitter, matching network: Galileo Avionica (Milan,Italy)
  • Antenna: Astro Aerospace (Carpinteria,CA, USA)

History[edit]

While the initial studies date back to 2001, full-scale development was released only in February 2003. The Engineering Model (EM) of the instrument was delivered toLockheed Martin Space SystemsinDenver(responsible for the spacecraft) in March 2004, and integrated into the Orbiter Test Bed. TheProtoFlightModel (PFM) was delivered and integrated on theMars Reconnaissance Orbiterin Denver in September 2004. Mars Reconnaissance Orbiterwas launched fromCape Canaveral Air Force Stationon August 12, 2005, with anAtlas V-Centaurlaunch vehicle, and reachedMarsorbiton March 10, 2006. Theaerobrakingphase, needed to reach the operational orbit, lasted until August 30, 2006. On September 17, 2006, the SHARAD antenna was deployed, and the first in-flight test of theradarwas successfully carried out on September 19. SHARAD has been operational since November 2006.

Findings[edit]

Further information:Scalloped topography

The SHARAD radar penetrated the north polar layered ice deposits of Mars and revealed a relatively small (about 100 meter) maximum deflection of the underlying rock, which suggests a stronglithospheregreater than 300 kilometers thick.[2]Radar results consistent with massive deposits of water ice in middle latitudes support a debris-covered glacier hypothesis.[3]

On November 22, 2016, NASA reported finding a large amount ofunderground icein theUtopia Planitiaregion of Mars using SHARAD. The volume of water detected has been estimated to be equivalent to the volume of water inLake Superior.[4][5][6]

Mars- Utopia Planitia
Scalloped terrain led to the discovery of a large amount ofunderground ice
enough water to fillLake Superior(November 22, 2016)[4][5][6]
Martian terrain
Map of terrain

The calculations for the volume of water ice in the region were based on measurements from SHARAD, the ground-penetrating radar instrument on theMars Reconnaissance Orbiter(MRO).

SHARAD finds ice by measuring its radar returns from the surface and from a deeper lower surface. The depth to the lower surface was found from HiRISE images of gaps in the surface.

SHARAD radar data when combined to form a 3D model reveal buried craters in the north polar cap. These may be used to date certain layers.[7]

Research, published in April 2011, described a large deposit of frozen carbon dioxide near the south pole. Most of this deposit probably enters Mars' atmosphere when the planet's tilt increases. When this occurs, the atmosphere thickens, winds get stronger, and larger areas on the surface can support liquid water. [8]After more analysis, it was discovered that if these deposits were all changed into gas, the atmospheric pressure on Mars doubles.[9]There are three layers of these deposits; each are capped with a 30-meter layer of water ice that prevents the CO2from sublimating into the atmosphere. Insublimationa solid material goes directly into a gas phase. These three layers are linked to periods when the atmosphere collapsed when the climate changed.[10]

Interactive Mars map[edit]

Map of MarsAcheron FossaeAcidalia PlanitiaAlba MonsAmazonis PlanitiaAonia PlanitiaArabia TerraArcadia PlanitiaArgentea PlanumArgyre PlanitiaChryse PlanitiaClaritas FossaeCydonia MensaeDaedalia PlanumElysium MonsElysium PlanitiaGale craterHadriaca PateraHellas MontesHellas PlanitiaHesperia PlanumHolden craterIcaria PlanumIsidis PlanitiaJezero craterLomonosov craterLucus PlanumLycus SulciLyot craterLunae PlanumMalea PlanumMaraldi craterMareotis FossaeMareotis TempeMargaritifer TerraMie craterMilankovič craterNepenthes MensaeNereidum MontesNilosyrtis MensaeNoachis TerraOlympica FossaeOlympus MonsPlanum AustralePromethei TerraProtonilus MensaeSirenumSisyphi PlanumSolis PlanumSyria PlanumTantalus FossaeTempe TerraTerra CimmeriaTerra SabaeaTerra SirenumTharsis MontesTractus CatenaTyrrhena TerraUlysses PateraUranius PateraUtopia PlanitiaValles MarinerisVastitas BorealisXanthe Terra
The image above contains clickable linksInteractive image mapof theglobal topography of Mars.Hoveryour mouseover the image to see the names of over 60 prominent geographic features, and click to link to them. Coloring of the base map indicates relativeelevations,based on data from theMars Orbiter Laser Altimeteron NASA'sMars Global Surveyor.Whites and browns indicate the highest elevations (+12 to +8 km); followed by pinks and reds (+8 to +3 km); yellow is0 km;greens and blues are lower elevations (down to−8 km).Axesarelatitudeandlongitude;Polar regionsare noted.


See also[edit]

  • LRS,Lunar radar sounder (LRS) is a orbiting low frequency radar sounder and altimeter over Earth's Moon
  • MARSIS,Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a orbiting low frequency radar sounder and altimeter over Mars
  • RIME,Radar for Icy Moons Exploration (RIME) is a orbiting low frequency radar sounder and altimeter for Jupiter's Icy moons
  • Tianwen-1,The Tianwen-1 mission plans an Orbiter Subsurface Radar (OSR) and rover based Ground-Penetrating Radar (GPR) for Mars
  • WISDOM (radar),Water Ice and Subsurface Deposit Observation on Mars (WISDOM) is a ground-penetrating radar on the ExoMars rover

References[edit]

  1. ^R. Oroseiet al.,"Science results from the MARSIS and SHARAD subsurface sounding radars on Mars and their relevance to radar sounding of icy moons in the Jovian system",EPSC2010-726, European Planetary Science Congress 2010, Vol. 5 (accessed Nov. 17 2014)
  2. ^Phillips, R. J.; Zuber, M. T.; Smrekar, S. E.; Mellon, M. T.; Head, J. W.; Tanaka, K. L.; Putzig, N. E.; Milkovich, S. M.; Campbell, B. A.; Plaut, J. J.; Safaeinili, A.; Seu, R.; Biccari, D.; Carter, L. M.; Picardi, G.; Orosei, R.; Mohit, P. S.; Heggy, E.; Zurek, R. W.; Egan, A. F.; Giacomoni, E.; Russo, F.; Cutigni, M.; Pettinelli, E.; Holt, J. W.; Leuschen, C. J.; Marinangeli, L. (2008)."Mars north polar deposits: stratigraphy, age, and geodynamical response".Science.320(5880): 1182–1185.Bibcode:2008Sci...320.1182P.doi:10.1126/science.1157546.hdl:11573/69689.PMID18483402.S2CID6670376.
  3. ^Holt, J. W.; Safaeinili, A.; Plaut, J. J.; Head, J. W.; Phillips, R. J.; Seu, R.; Kempf, S. D.; Choudhary, P.; Young, D. A.; Putzig, N. E.; Biccari, D.; Gim, Y. (2008). "Radar Sounding Evidence for Buried Glaciers in the Southern Mid-Latitudes of Mars".Science.322(5905): 1235–1238.Bibcode:2008Sci...322.1235H.doi:10.1126/science.1164246.PMID19023078.S2CID36614186.
  4. ^abStaff (November 22, 2016)."Scalloped Terrain Led to Finding of Buried Ice on Mars".NASA.RetrievedNovember 23,2016.
  5. ^ab"Lake of frozen water the size of New Mexico found on Mars – NASA".The Register.November 22, 2016.RetrievedNovember 23,2016.
  6. ^ab"Mars Ice Deposit Holds as Much Water as Lake Superior".NASA. November 22, 2016.RetrievedNovember 23,2016.
  7. ^Foss, F., et al. 2017. 3D imaging of Mars'polar ice caps using orbital radar data. The Leading Edge: 36, 43-57.
  8. ^"NASA Spacecraft Reveals Dramatic Changes in Mars' Atmosphere".[permanent dead link]
  9. ^Phillips, R., et al. 2011. Massive CO2ice deposits sequestered in the south polar layered deposits of Mars. Science: 332, 638-841
  10. ^Bierson, C., et al. 2016. Stratigraphy and evolution of the buried CO2depositin the Martian south polar cap. Geophysical Research Letters: 43, 4172-4179

Further reading[edit]

External links[edit]

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