@prefix skos: . skos:definition """Many modern radio clocks use the Global Positioning System to provide more accurate time than can be obtained from these terrestrial radio stations. These GPS clocks combine time estimates from multiple satellite atomic clocks with error estimates maintained by a network of ground stations. Due to effects inherent in radio propagation and ionospheric spread and delay, GPS timing requires averaging of these phenomena over several periods. No GPS receiver directly computes time or frequency, rather they use GPS to discipline an oscillator that may range from a quartz crystal in a low-end navigation receiver, through oven-controlled crystal oscillators (OXCO) in specialized units, to atomic oscillators (rubidium) in some receivers used for synchronization in telecommunications. For this reason, these devices are technically referred to as GPS-disciplined oscillators. Group: Instrument_Details Entry_ID: GPS CLOCKS Group: Instrument_Identification Instrument_Category: Earth Remote Sensing Instruments Instrument_Class: Passive Remote Sensing Instrument_Type: Positioning/Navigation Instrument_Subtype: GPS Short_Name: GPS CLOCKS End_Group Group: Instrument_Associated_Sensors Short_Name: GPS End_Group Group: Associated_Platforms Short_Name: GPS End_Group Online_Resource: http://www.kema.com/Default.aspx Creation_Date: 2010-08-31 End_Group"""@en ; skos:prefLabel "GPS CLOCKS"@en ; skos:inScheme ; skos:broader ; a skos:Concept . skos:prefLabel "GPS"@en ; a skos:Concept ; skos:narrower .