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 • 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)
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
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
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
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
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
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)
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
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.
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
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.
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
