Pôle multimédia 2015-419 - CNES Toulouse - © Phtothèque ACM tiniest distortions oftheEarth. are essential for studying theshapeandeven the International Terrestrial Reference Frame (ITRF), data itprovides, whichare usedto determine the vital importance for geodesyandgeophysics.The is alsoahighly accurate positioningsystem, of that are accurate to the nearest centimetre. DORIS from thesetools, byproviding orbital elements enabled scientists to exploit allofthedata derived the beginningof1990s,DORISsystem has need information aboutitsexact position.Since satellite’s altimetryinstruments, scientists also able to exploit thevaluable data collected bya the Earthanditsoceans, lakes andrivers. To be S pace isanexcellent observatory for studying THE SPACESURVEYOR for observingandstudying ourplanet. thus contributing to thesuccess offuture missions take onnew challenges duringtheyears to come, of theEarthfrom space, DORISwillcontinue to with thePleiades satellites. Asagenuinesurveyor the ChineseHY-2Amission, oraccurate imaging Cryosat, theFrench-Indian SARAL-AltiKasatellite, Jason satellites, ortheESAsatellites Envisatand French-American seriesofTOPEX/Poseidon and oceanography, glaciology, hydrology withthejoint results ofobservation missions, whetherfor DORIS thusplaysamajorrole intheremarkable accuracy. measurements andensurestheir the entiresystem,time-tags the instrument’sclockandkeyto shifts. Anultra-stableoscillator, measures theDopplerfrequency satellite flies.Anelectronicreceiver by thestationsoverwhich ground, receivesradiowavessent An antenna,pointingtowardthe On thesatellite: The components oftheDORISsystem the satellites. space, whichispickedupby directional radiosignalinto the globe,eachemitanomni- distributed evenlyaround Some sixtypermanentstations, On theground: MESURING FROM SPACE TO WITHIN A CENTIMETRE

A TAILOR-MADE SYSTEM THAT HAS PROVED ITS AN EXPANDING PROCESSING CENTRE, PLUS A WORTH GROWING CONSTELLATION OF SATELLITES The DORIS system (Doppler determination The data acquired and stored on satellites are and Radio-positioning Integrated on Satellite) was periodically transmitted to SSALTO, the multi- designed and developed by CNES jointly with the mission orbitography and altimetry centre located French National Geographic Institute (IGN) and in Toulouse. It monitors stations to ensure that the Research Group for Space (GRGS) to they are operating correctly, processes all the determine the exact position of satellites on their measurement data, determines the orbit of the and precisely locate terrestrial stations. instrument-carrying satellites, then archives and distributes the data. AN EXEMPLARY NETWORK OF STATIONS Since 1990, a dozen satellites, with four always A network of independent stations was deployed in orbit simultaneously since 2002, have provided throughout the world in 1986. They are used as measurements that are then exploited by the ground control points, to provide continuous cove- international scientific community. There are rage of satellite trajectories. Thanks to exemplary currently five contributing satellites in orbit, and international cooperation, the DORIS system has the future missions being prepared will ensure a network of about sixty stations spread evenly that a DORIS constellation continues to fly around the world. beyond 2030.

MONITORING AND MAINTAINING THE SYSTEM At the system level, DORIS has undergone various far-reaching developments and improvements: in particular, the integrity-monitoring team can immediately ensure a remote detection of a faulty station, or its first signs of aging, well before its performance starts to decline.

Working in synergy with this team, the IGN carries out maintenance work on the network to improve the performance of the stations and ensure they remain compliant with the current requirements of the system. The homogeneity, reliability, maintenance, and constant upgrades

DORIS MISSIONS

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Spot 2 [D1] Topex [D1, S, G] Spot 3 Spot 4 [D1] Jason 1 [D2, S, G] [D2, S] Spot 5 [D2] Jason 2 [DX, S, G] Cryosat 2 [DX, S] HY-2A [DX, S, G] HY-2B Saral [DX, S] Sentinel 3A [DXs, S, G] Past missions Sentinel 3B Current missions Sentinel 3C Future missions agreed/nominal lifetime Sentinel 3D Future missions pending approval Jason 3 [DXs, S, G] On board instruments: Jason-CS1/Sentinel 6A [DXs, S, G] D1, D2, DX, DXs: DORIS/versions Jason-CS2/Sentinel 6A S: SLR, G: GNSS Swot [DXs, S, G] Pôle multimédia 2015-419 - CNES Toulouse - © Phtothèque ACM - © Phtothèque Toulouse Pôle multimédia 2015-419 - CNES TRACKING THE EARTH’S MOVEMENTS

The constant improvement of DORIS has made it a benchmark for precision orbitography, which is a crucial aspect of altimetry applications, ranging from operational oceanography, modelling to climatic studies.

From geodesy to geophysics DORIS has made good use of its unique network of stations and its highly accurate positioning capability, to address the needs of geodesy and geophysics.

http://www.iers.org

Monitoring the level of Determining the movement Participating in the the oceans of tectonic plates International Terrestrial Reference Frame (ITRF)

Observing the Measuring variations Understanding And even more movements in the Earth’s the movement of applications... of volcanoes rotation axis the Earth’s centre of masse (the geocentre)

Sites ITRF : VLBI + SLR + DORIS + GNSS 90° 90°

60° 60°

30° 30°

0° 0°

-30° -30°

-60° -60°

-90° -90° VLBI SLR GNSS DORIS Pôle multimédia 2015-419 - CNES Toulouse - © Phtothèque ACM - © Phtothèque Toulouse Pôle multimédia 2015-419 - CNES

http://ids-doris.org