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

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ecords in both stations <strong>the</strong> contribution <strong>of</strong> <strong>the</strong> satellite clock vanishes, not biasing with its errors<strong>the</strong> time comparison. At present, GPS C/A-code common-views allow to obtain 2-10 ns level intime synchronization. The common-view method reduces some uncertainties <strong>of</strong> physical originand, a factor which was relevant until <strong>the</strong> middle <strong>of</strong> <strong>the</strong> year 2000, it cancelled <strong>the</strong> deliberatedegradation introduced in GPS time (Selective Availability), with this degradation beingeliminated on 2 May 2000.263. GPS observations are dependent on <strong>the</strong> effects <strong>of</strong> <strong>the</strong> propagation medium on <strong>the</strong> signal.One channel GPS C/A-code time receivers track one satellite at a time. As <strong>the</strong> C/A-code istransmitted in only one frequency, <strong>the</strong>re is no possibility to determine <strong>the</strong> delay introduced by <strong>the</strong>propagation <strong>of</strong> <strong>the</strong> signal along <strong>the</strong> ionosphere. Much progress has been done by using <strong>the</strong>International GPS Service (IGS) products to correct GPS data. All <strong>the</strong> GPS common viewsobtained with single-frequency receivers in TAI are corrected by using <strong>the</strong> IGS total electroncontent (TEC) maps. All GPS links in TAI are corrected using IGS precise satellite ephemeredes.264. During 2003, GPS multi-channel dual-frequency receivers had been incorporated into <strong>the</strong>network <strong>of</strong> time links for TAI: BIPM had four <strong>of</strong> <strong>the</strong>se links <strong>of</strong>ficially in <strong>the</strong> calculation in June2004, with uncertainties <strong>of</strong> 1 ns or less.265. The BIPM establishes and distributes twice a year schedules for <strong>the</strong> observation <strong>of</strong> GPSsatellites. These schedules are necessary to organize <strong>the</strong> common views that are <strong>the</strong> basis <strong>of</strong> <strong>the</strong>clock links.266. The development <strong>of</strong> multi-channel multi-code receivers permits to increase in an order<strong>of</strong> magnitude <strong>the</strong> number <strong>of</strong> observations with respect to <strong>the</strong> single-channel mode. Multi-channelC/A-code receivers observe all GPS satellites in view using 13-minute tracks every 16 minutes at<strong>the</strong> standard hours. No GPS schedule is necessary to programme <strong>the</strong> observations since <strong>the</strong>receiver automatically tracks all satellites in view. Data are stored in a single file with astandardized format. Under this constraint, <strong>the</strong> number <strong>of</strong> satellite tracks increases by a factor <strong>of</strong>10 with respect to <strong>the</strong> number <strong>of</strong> single-channel common-view tracks. This implies animprovement in <strong>the</strong> quality <strong>of</strong> time and frequency transfer. However, multi-channel observationsmay be subject to systematic variations. Environmental conditions affect receivers by imposingsystematic effects. Temperature stabilized antennas (TSA) have been developed at <strong>the</strong> BIPM andare currently commercially available.267. TWSTFT is a technique that allows <strong>the</strong> comparison <strong>of</strong> two distant clocks by using astransponder a geostationary telecommunications satellite. The <strong>the</strong>oretical precision expected intime transfer <strong>of</strong> several hundred picoseconds has been reached in <strong>the</strong> first semester <strong>of</strong> 2004, when<strong>the</strong> time laboratories operating TWSTFT stations in Europe and North America startedscheduling daily and sub-daily observations.268. The network <strong>of</strong> clock comparisons at <strong>the</strong> BIPM is at present supported by common viewson GPS satellites and by links using TWSTFT.Future prospects269. The stability <strong>of</strong> <strong>the</strong> atomic time scale has been improved due to <strong>the</strong> replacement in mostlaboratories <strong>of</strong> <strong>the</strong> old caesium clocks by <strong>the</strong> more high-performance new-type ones. Thealgorithm used in <strong>the</strong> calculation <strong>of</strong> TAI assigns relative weights to participating clocks, thusassuring that <strong>the</strong> stability is highly dominated by <strong>the</strong> best clocks. Primary frequency standards48
measurements are used to evaluate <strong>the</strong> departure <strong>of</strong> <strong>the</strong> scale unit <strong>of</strong> TAI relative to <strong>the</strong> SI second;<strong>the</strong>y are ei<strong>the</strong>r excellent commercial caesium clocks or clocks developed at some laboratorieswhich have long-term stability. Time transfer techniques need to be accurate enough for <strong>the</strong>comparison <strong>of</strong> precise clocks. GPS C/A-code single-channel and multi-channel common viewsplus TWSTFT are used to compare <strong>the</strong> clocks participating in TAI, leading to a stability <strong>of</strong> about2 parts in 10 15 for periods <strong>of</strong> about one month.270. Clock comparison by using <strong>the</strong> GLONASS satellites could be used in <strong>the</strong> future in TAI,provided that <strong>the</strong> Russian satellite constellation be complete and stable.271. The number <strong>of</strong> common views, when using multi-channel GPS/GLONASS receivers,increases in a factor <strong>of</strong> 20 with respect to single-channel one-system mode. Both GPS andGLONASS observations can be combined, provided that <strong>the</strong> differences between <strong>the</strong> systems areminimized. At <strong>the</strong> basis, <strong>the</strong> two systems adopt different references for space and time. WhileGPS is steered on UTC (USNO), GLONASS relies on UTC (SU). The terrestrial framesrespectively adopted (ITRF for GPS and PZ-90 for GLONASS) differed up to 20m. Following<strong>the</strong> recommendations <strong>of</strong> <strong>the</strong> International Committee <strong>of</strong> Weights and Measures (CIPM) in 1996,efforts have been made to synchronise GLONASS time reference as close as possible to UTC,and to bring GLONASS terrestrial references in conformity to <strong>the</strong> ITRF.272. A stability <strong>of</strong> about 200ps could be achieved using <strong>the</strong> precise code transmitted by <strong>the</strong>GLONASS system in a single-channel mode. This value is reduced by a half when operation inmulti-channel mode on short baselines takes place.273. GLONASS P-code has two clear advantages. The chip length being 1/5 th that <strong>of</strong> GPSC/A-code allows more precise pseudo-range measurements. As <strong>the</strong> precise code is transmitted inboth L1 and L2 frequencies, <strong>the</strong> ionospheric delays can be precisely determined.274. The BIPM expects, in <strong>the</strong> future, to take advantage <strong>of</strong> <strong>the</strong> existence <strong>of</strong> independent globalnavigation satellite systems to have redundant clock comparisons, thus making <strong>the</strong>m morereliable. The GLONASS satellites cannot be at present <strong>of</strong>ficially used for <strong>the</strong> construction <strong>of</strong> <strong>the</strong>international time scales since <strong>the</strong> system does not completely satisfy <strong>the</strong> stability required for <strong>the</strong>purpose. Studies are undertaken at <strong>the</strong> BIPM concerning <strong>the</strong> utilisation <strong>of</strong> GLONASS precisecodefor clock comparison. GALILEO will certainly bring much improvement to <strong>the</strong> internationaltime links for TAI.International Federation <strong>of</strong> Surveyors (FIG)What is FIG?275. The International Federation <strong>of</strong> Surveyors (FIG – French acronym) is a federation <strong>of</strong>national pr<strong>of</strong>essional surveying associations and is <strong>the</strong> only international body that represents allsurveying disciplines. FIG was founded in 1878 in Paris. It is recognised as a non-governmentalorganization by <strong>the</strong> United Nations. Over 110 countries are represented in FIG. In addition, <strong>the</strong>reare 230,000 surveyors around <strong>the</strong> world in <strong>the</strong> Member Associations.The technical work <strong>of</strong> FIG276. The following 10 Commissions carry out <strong>the</strong> technical work <strong>of</strong> FIG:1. Pr<strong>of</strong>essional Standards and Practice.49
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 and 52: • Provide consultancy and advice
Page 53: 255. Methods to compare distant clo
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
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Annex I: Indian universities, resea
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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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