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The IGS Network

The IGS Network. Angelyn Moore IGS Central Bureau Jet Propulsion Laboratory USA. Contents. Stations Data Retrieval and Quality Checks Summary Information Files Network Coordination. Equipment at the IGS Stations. Requirements are stated in

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The IGS Network

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  1. The IGS Network Angelyn Moore IGS Central Bureau Jet Propulsion Laboratory USA

  2. Contents • Stations • Data Retrieval and Quality Checks • Summary Information Files • Network Coordination

  3. Equipment at the IGS Stations • Requirements are stated in • http://igscb.jpl.nasa.gov/network/guide_igs.html • Emphasis is on performance characteristics. • Some key examples: • • [Receiver] Dual-frequency code and phase with AS on or off • • [Receiver] At least 8 channels • • [Receiver] At least 30 second sampling rate • • [Receiver] Observation synchronization +/- 1 ms of true GPS time • • [Monument] First-order geodetic monument with respect to stability, • durability, maintenance, documentation, and access • • [Monument] IERS DOMES number from domes@lareg.ensg.fr orhttp://lareg.ensg.ign.fr/ITRF/domesreq.html • • [Site] Minimal obstruction to at least 15 degrees elevation • • Recommendation: meteorological or weatherinstruments (especially precise Barometer)

  4. Data Retrieval Methods Vary • Receiver -> modem -> phone line -> modem -> computer • Receiver -> computer -> internet -> computer • Receiver -> wireless -> computer -> internet -> computer • Receiver > VSAT > computer • Operator's choice based on available infrastucture, cost, & benefits • . . . but low latencies are always preferred

  5. Application Networks • Sites which meet additional requirements will be attractive to the specialized Working Group and Pilot Project applications. • Ultra-rapid products/Low Earth Orbiter • Data submission must be at least hourly; 1 second sampling time • Troposphere Working Group • Meteorological instruments including precise barometer • (recommended for all stations!) • Time Transfer Pilot Project • Suitable receivers, external precise frequency standard (cesium or preferably H maser); • special care in cabling with respect to temperature stability and • reporting of cable changes

  6. Initiation of Operations • Clear a 4-character site ID with the Central Bureau • Fill out a site log according to • ftp://igscb.jpl.nasa.gov/station/general/blank.log • Submit site log and sample RINEX to CB • When log is approved and available at CB, begin submitting data to a Data Center and notify the community with an IGSMail

  7. OngoingSite Log duties • Keep the site log correct and current. Email updates within one day of a major update to the site. • Email the log to igscb@igscb.jpl.nasa.gov or utilize the automatic submission method described at • http://igscb.jpl.nasa.gov/network/sitelog-submissions.html • Observe the format. Choose equipment names from the official list at ftp://igscb.jpl.nasa.gov/station/general/rcvr_ant.tab

  8. Ongoing Data Monitoring Duties • Data quality should be established before transmission to • Data Center • Suggest simple monitoring for anomalies: • Herb Dragert's "11 fields to monitor" • Site ID Sample Rate • Year Number of observations • Julian day Number of gaps • Start Time Number of cycle slips • Stop Time Multipath • *mean ionospheric variations (narrowlane noise normalized by sample rate) • 10 of these are available from teqc +qc and do not require ephemerides • (seehttp ://www.unavco.ucar.edu/software) • CDDIS provides such data at • ftp://cddisa.gsfc.nasa.gov/pub/reports/gpsstatus • but operators should pre-monitor

  9. Ongoing Data Submission Duties • Archive raw tracking data • Keep current with RINEX format (defined at ftp://igscb.jpl.nasa.gov/igscb/data/format) and your RlNEX conversion software • Submit daily RINEX to a Data Center by 0200 UT • Information in RINEX header (antenna, DOMES, receiver, height) must be correct and match the site log • Avoid data resubmission but if itis necessary, send an IGSMail • An upcoming request: be ready to switch to an alternate Data Center within 1 business day, in case of major Data Center inavailability • Observe evolving IGS recommendations such as for observables • in RINEX from newer codeless receivers (see next slide)

  10. Transition to Codeless Receivers • Following IGSMail #2235: • Older IGS receivers such as AOA Rogue and TurboRogue track • 4 quantities: • C1 = C/A code at L1 frequency • L1(C1) = C/A-based phase at L1 frequency • P2-P1 = cross-correlated pseudorange • L2-L1 = phase difference • and report 4 observables: • C1P2’ = C1 + (P2-P1) • L1(C1)L2’= L1(C1)+(L2-L1) • Codeless receivers, e.g. AOA Benchmark, Ashtech Z-XII track 6 observables: • C1 and L1 (C1) • P1 = Y1-codeless pseudorange at L1 frequency • L1 (P1) = Y1-codeless-based phase at L1 frequency • P2 = Y2-codeless pseudorange at L2 frequency • L2(P2) = Y2-codeless-based phase at L2 frequency

  11. Transition to Codeless Receivers • The Problem: Use of the codeless P1 and P2 observables before April 02, 2000 (Wk 1056) or c1 and PZ’ after April 02, 2000 introduces a satellite-dependent bias (~2 ns) in ionosphere-free pseudoranges. Clock products and point positioning become corrupted in an unpredicable way when biased and unbiased (codeless and cross-correlated) measurements are mixed. • Since April 02 (Wk 1056) the P1, P2 observables should be used with all IGS products and operators should be providing them to IGS. See IGS Mail #2744 for more details and how to form P1, P2 when only cross-correlated-styles C1, P2’ are available.

  12. Commonly Used Summaries • • SINEX template • Generated at CB from current site logs • Provides tabulation of station parameters vs. time for input to analysis • • yyddd.status and check_* files at CDDIS • Simple teqc reports and latency reports • • igsnet • weekly email from CB with each station's Quality, Quantity, Latency • QualityQuantityLatency • valid clocks > 250 Avg. # valid clocks Avg. in hrs • <100 phase bias resets • 3D formal location err < 1 cm • rms pseudorange residuals <86cm • pseudorange meas. > .9*phase meas. • rms phase residuals <13nm

  13. Role of Network Coordinator • Coordination and liason functions as regards the network as a whole • between station operators, users, data centers, and analysts • ? Questions, concerns, suggestions are always welcome! • Examples: • I need to relocate my monument. How can I make the change gosmoothly for the analysts? • I am not able to get hourly data quickly enough in Europe. • Why did my station’s quality score decrease? • The SINEX template does not have a phase center for the antenna at station ABCD.

  14. Questions? • Angelyn Moore • IGS Network Coordinator & • Deputy Director, Central Bureau • Jet Propulsion Laboratory • 4800 Oak Grove Drive, M/S 238-540 • Pasadena, California 91109 USA • Angelyn.W.Moore@jpl.nasa.gov

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