report of the action team on global navigation satellite systems (gnss)

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diplomatic treaty between fifty-one nations, by operating through a series <strong>of</strong> ConsultativeCommittees, whose members are <strong>the</strong> national metrology institutes <strong>of</strong> <strong>the</strong> member states <strong>of</strong> <strong>the</strong>Convention, through its own laboratory work. The BIPM carries out measurement-relatedresearch. It takes part in, and organises international comparisons <strong>of</strong> national measurementstandards, carrying out calibrations for Member States.247. The International System <strong>of</strong> Units (SI): The 11 th “Conférence Générale des Poids etMesures” (1960) adopted <strong>the</strong> name “Système International d'Unités” (International System <strong>of</strong>Units, international abbreviation SI), for <strong>the</strong> recommended practical system <strong>of</strong> units <strong>of</strong>measurement. The 11 th CGPM laid down rules for <strong>the</strong> prefixes, <strong>the</strong> derived units, and o<strong>the</strong>rmatters.248. The base units are a choice <strong>of</strong> seven well-defined units which by convention are regardedas dimensionally independent: <strong>the</strong> metre, <strong>the</strong> kilogram, <strong>the</strong> second, <strong>the</strong> ampere, <strong>the</strong> kelvin, <strong>the</strong>mole, and <strong>the</strong> candela. Derived units are those formed by combining base units according to <strong>the</strong>algebraic relations linking <strong>the</strong> corresponding quantities. The names and symbols <strong>of</strong> some <strong>of</strong> <strong>the</strong>units thus formed can be replaced by special names and symbols which can <strong>the</strong>mselves be used t<strong>of</strong>orm expressions and symbols <strong>of</strong> o<strong>the</strong>r derived units.249. The SI is not static but evolves to match <strong>the</strong> world's increasingly demanding requirementsfor measurement.250. Regarding scientific activities, <strong>the</strong> scientific work at <strong>the</strong> BIPM centres on seven principaltopics: length, mass, time, electricity, radiometry and photometry, ionizing radiation andchemistry. In addition, a small activity is maintained in <strong>the</strong>rmometry and in <strong>the</strong> measurement <strong>of</strong>pressure and humidity to meet <strong>the</strong> internal needs <strong>of</strong> <strong>the</strong> BIPM laboratories.251. The Time Section <strong>of</strong> <strong>the</strong> BIPM calculates and disseminates <strong>the</strong> two conventional timescales, International Atomic Time (TAI) and Coordinated Universal Time (UTC). Both scales areelaborated on <strong>the</strong> basis <strong>of</strong> clock data from laboratories distributed worldwide.252. A network <strong>of</strong> stations is organised to allow distant clock comparison. Two methods areused at present in TAI to compare remote clocks: time transfer by using <strong>the</strong> constellation <strong>of</strong>Global Positioning System (GPS) satellites, and two-way satellite time and frequency transfer(TWSTFT). Research work is conducted at <strong>the</strong> Time Section to improve <strong>the</strong> quality <strong>of</strong> <strong>the</strong> timelinks. The BIPM, jointly with <strong>the</strong> International GPS Service (IGS), have investigated <strong>the</strong>utilisation <strong>of</strong> GPS geodetic-type receivers in TAI; as one <strong>of</strong> <strong>the</strong> conclusions <strong>of</strong> this work, timelinks by using dual-frequency multi-channel GPS geodetic-type receivers have been incorporatedto TAI. Time transfer by using GLONASS satellites is also under study.253. International Atomic Time is <strong>the</strong> uniform time scale calculated at <strong>the</strong> Time Section <strong>of</strong> <strong>the</strong>BIPM since 1988. The unit <strong>of</strong> TAI is <strong>the</strong> second <strong>of</strong> <strong>the</strong> International System <strong>of</strong> units (SI), definedas a fr<strong>action</strong> <strong>of</strong> <strong>the</strong> period <strong>of</strong> an atomic transition; it is realised on <strong>the</strong> basis <strong>of</strong> <strong>the</strong> measurements<strong>report</strong>ed by laboratories operating primary frequency standards.254. GNSS have a key role in time dissemination and in clock comparison. The navigationmessage broadcast by <strong>the</strong> GPS satellites provides access to precise time. The GPS time is <strong>the</strong> timescale elaborated by combining <strong>the</strong> ensemble <strong>of</strong> clocks operating for that purpose. It is steered toUTC (USNO), one <strong>of</strong> <strong>the</strong> best local representations <strong>of</strong> UTC.46
255. Methods to compare distant clocks are necessary to calculate <strong>the</strong> clock differences whichare <strong>the</strong> base <strong>of</strong> <strong>the</strong> computation <strong>of</strong> TAI. In <strong>the</strong> last decade, <strong>the</strong> time community has largelyexploited <strong>the</strong> Global Positioning System (GPS) satellites for time transfer using receivers adaptedfor time comparisons. In 1981, <strong>the</strong> first GPS time links were introduced in TAI. The technique,still in use today, was <strong>the</strong> GPS common-view single channel C/A-code. It allows time comparisonwith an uncertainty <strong>of</strong> one part in 10 14 for average times <strong>of</strong> a few days. The stability reached byTAI for periods <strong>of</strong> a month is <strong>of</strong> two parts in 10 15 .256. In <strong>the</strong> last years, multi-channel GPS and GPS-GLONASS receivers have beencommercially developed. The stability <strong>of</strong> time transfer increases in a factor <strong>of</strong> about three whenmulti-channel satellite observations are used. GLONASS P-code signal has always been availableto civil users; it has been demonstrated that it reduces <strong>the</strong> noise level by a factor <strong>of</strong> about fiverelative to GPS C/A-code time comparisons.257. The GPS carrier-phase technique allows frequency comparison at a level <strong>of</strong> one part in10 15 , and it will be a useful tool in accurate time transfer after some remaining problems beinvestigated and solved.258. The technique <strong>of</strong> two way time and frequency transfer by telecommunication satellite(TWSTFT) has been largely investigated: in optimal conditions (daily and sub-dailyobservations) it has a better performance than <strong>the</strong> GPS C/A single/multi-channel single frequencytime transfer techniques used in TAI. About ten TWSTFT links are used at present in <strong>the</strong>calculation <strong>of</strong> TAI.Present organization <strong>of</strong> time links259. The establishment <strong>of</strong> TAI and UTC is based on atomic clock data coming fromworldwide distributed laboratories, and <strong>the</strong>refore it is strongly dependent on <strong>the</strong> means <strong>of</strong> timecomparison. The international time scales computed at <strong>the</strong> BIPM are based on data <strong>of</strong> some 220clocks located in about 50 time laboratories distributed all over <strong>the</strong> world. The quality <strong>of</strong> clocksparticipating in TAI has evolved in <strong>the</strong> last decade, with <strong>the</strong> development <strong>of</strong> more precisecaesium commercial clocks. Caesium clocks <strong>of</strong> <strong>the</strong> new type are stable in about one part in 10 14over periods <strong>of</strong> a day. Very accurate methods <strong>of</strong> time transfer are necessary so that <strong>the</strong>comparison does not degrade <strong>the</strong> accuracy <strong>of</strong> <strong>the</strong> atomic clocks.260. The present organization <strong>of</strong> <strong>the</strong> international time links at <strong>the</strong> BIPM is based on two-timecomparison techniques: common views on GPS satellites and TWSTFT.261. The introduction <strong>of</strong> GPS into time transfer in <strong>the</strong> 1990’s led to an improvement <strong>of</strong> oneorder or more <strong>of</strong> magnitude with respect to o<strong>the</strong>r methods used at that moment for clocksynchronisation. Clock comparison plays a key role in <strong>the</strong> elaboration <strong>of</strong> <strong>the</strong> international timescales. Clocks situated at distant laboratories, spread all over <strong>the</strong> world, can be compared with anuncertainty <strong>of</strong> several nanoseconds by using GPS. About 80% <strong>of</strong> <strong>the</strong> clock comparisons for TAIare exclusively done by using <strong>the</strong> clocks on board GPS satellites, with <strong>the</strong> 20% remnant beingprovided by ano<strong>the</strong>r technique and <strong>the</strong> corresponding time link by GPS as a backup.262. The GPS common-view method is used in <strong>the</strong> calculation <strong>of</strong> time links at <strong>the</strong> BIPM. In<strong>the</strong> common-view technique, two stations simultaneously observe <strong>the</strong> same GPS satellite. Bothstations record <strong>the</strong> difference between each local clock and GPS time at <strong>the</strong> same instant andusing <strong>the</strong> same clock on board <strong>the</strong> satellite in common view. When making <strong>the</strong> difference <strong>of</strong>47
Page 1 and 2: REPORT OF THE ACTION TEAM ONGLOBAL
Page 3 and 4: This document has not been formally
Page 5 and 6: CONTENTSIntroduction ..............
Page 7 and 8: REPORT OF THE ACTION TEAMON GLOBAL
Page 9 and 10: Product4. The product of</s
Page 11 and 12: II.OVERVIEW OF PLANNED AND EXISTING
Page 13 and 14: virtually every facet of</s
Page 15 and 16: 27. Time and frequency disseminatio
Page 17 and 18: Service Availability Standard39. Th
Page 19 and 20: Table 1-4. Service Reliability Stan
Page 21 and 22: 50. The GPS Control Segment (CS) is
Page 23 and 24: Service Availability Standard62. Th
Page 25 and 26: 71. The GPS Navigation Message cons
Page 27 and 28: the Board, mainly
Page 29 and 30: • Vertical :• Velocity:• User
Page 31 and 32: • The network of
Page 33 and 34: 126. The EU and ESA have concluded
Page 35 and 36: • The Search and Rescue Service (
Page 37 and 38: invitation to tender to this effect
Page 39 and 40: 2. EGNOS169. As previously mentione
Page 41 and 42: 183. Three phases have been identif
Page 43 and 44: an air navigation service dedicated
Page 45 and 46: • Aviation: a representative desi
Page 47 and 48: 222. The information is openly avai
Page 49 and 50: 234. The United Nations Office for
Page 51: • Provide consultancy and advice
Page 55 and 56: measurements are used to evaluate <
Page 57 and 58: market can begin to develop. That a
Page 59 and 60: Nations and voluntary contributions
Page 61 and 62: IV.GNSS APPLICATIONSA. General appl
Page 63 and 64: 317. Agricultural applications incl
Page 65 and 66: 326. The regional activity in <stro
Page 67 and 68: GNSS SBAS-WAAS trials in th
Page 69 and 70: 356. Other activit
Page 71 and 72: with respect to the</strong
Page 73 and 74: 379. Argentina has at present a “
Page 75 and 76: Brazilian Continuous GPS Network (R
Page 77 and 78: all mapping-related works in <stron
Page 79 and 80: monitoring, national reference <str
Page 81 and 82: Programs: B.Sc/M.Sc/Ph.D. in geomat
Page 83 and 84: • University of
Page 85 and 86: V. NEEDS AND CONCERNS OF DEVELOPING
Page 87 and 88: Surveying, Mapping, Land Use• Pre
Page 89 and 90: include Special Implementation Proj
Page 91 and 92: VI.EXISTING TRAINING OPPORTUNITIES
Page 93 and 94: 465. Many other GN
Page 95 and 96: • Theory and practice of<
Page 97 and 98: D. GNSS training opportunities <str
Page 99 and 100: VII.INSTITUTIONAL MODELS FOR INTERN
Page 101 and 102: Environment Programme (UNEP), and <
Page 103 and 104:
appropriate national security reaso
Page 105 and 106:
VIII.RECOMMENDATIONS541. A number <
Page 107 and 108:
for Outer Space Affairs, developmen
Page 109 and 110:
• Develop the sk
Page 111 and 112:
Recommendation 2. The development <
Page 113 and 114:
583. The need to develop th
Page 115 and 116:
589. Project 2:Pilot Projects (4 pr
Page 117 and 118:
Annex I: Indian universities, resea
Page 119 and 120:
University/researchinstitute/compan
Page 121 and 122:
Annex III: Italian universities and
Page 123 and 124:
Annex IV: Italian non-governmental
Page 125 and 126:
Annex IV: Italian non-governmental
Page 127 and 128:
APPENDIXList of we
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report of the action team on global navigation satellite systems (gnss)

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