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    <skos:prefLabel xml:lang="en">POSEIDON-3</skos:prefLabel>
    <skos:definition xml:lang="en">The Poseidon-3 radar altimeter is the main instrument on the Jason-2 mission. Derived from the Poseidon-1 altimeter on Topex/Poseidon and the Poseidon-2 on Jason-1, it measures sea level, wave heights and wind speed.The Poseidon-3 altimeter emits pulses at two frequencies 13.6 and 5.3 GHz to measure the distance from the satellite to the surface (range). Free electrons in the atmosphere can delay the signal&apos;s return, affecting the measurement accuracy. The delay is directly related to the radar frequency, so the difference between the two measurements can be used to determine atmospheric electron content. Poseidon-3 is coupled with Doris/Diode, to improve measurements over coastal areas, inland waters and ice.Additional information on the Poseidon-3 instrument is available on the AVISO site.http://www.aviso.oceanobs.com/en/missions/current-missions/jason-2/instruments/poseidon-3/index.html[Description Source:  NASA JPL Ocean Surface Topography from Space Home Page]Group: Instrument_Details   Entry_ID: POSEIDON-3   Group: Instrument_Identification      Instrument_Category: Earth Remote Sensing Instruments      Instrument_Class: Active Remote Sensing      Instrument_Type: Altimeters      Instrument_Subtype: Radar Altimeters      Short_Name: POSEIDON-3      Long_Name: JASON-2 RADAR ALTIMETER   End_Group   Group: Associated_Platforms      Short_Name: OSTM/JASON-2   End_Group   Group: Spectral_Frequency_Information      Spectral_Frequency_Resolution: 13.6 GHz in the Ku-band, 5.3 GHz in the C-band   End_Group   Online_Resource: http://sealevel.jpl.nasa.gov/mission/ostm-sc-inst.html   Online_Resource: http://www.aviso.oceanobs.com/en/missions/current-missions/jason-2/instruments/poseidon-3/index.html   Sample_Image: http://sealevel.jpl.nasa.gov/gallery/spacecraft/images/ostm-altimeter-br.jpg   Creation_Date: 2008-07-10   Group: Instrument_Logistics      Instrument_Owner: France/CNES      Instrument_Owner: USA/NASA   End_GroupEnd_Group</skos:definition>
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