IGS Analysis Center Workshop - IGS - NASA

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Table 1. Current IGS Analysis Centers.COD Center for Orbit Determination in Europe SwitzerlandEMR Energy, Mines & ResourcesCanadaESA European Space AgencyGermanyGFZ GeoForschungsZentrum GermanyJPL Jet Propulsion LaboratoryUSANGS National Geodetic SurveyUSAS10 Scripps Institution of Oceanography USA2. Current ProductsTable 2 summarizes products regularly produced by the Analysis Centers. The standard forfilenamesisxxxwwwwd.extwhere xxx is a3-character Analysis Center identifier (see Table l), wwwwa4-digit GPS weeknumber, da l-digit day-of-week (O means Sunday, 6means Saturday, 7 means the entire week),and extisa 3-character identifier to denote file ’’type”. Forexample, esa07 137.erp indicates earthrotation parameters (.erp) by the European Space Agency for theentire GPS week 713. Otherextensions include .eph, .spl ,and .sp3forprecise GPS ephemerides, and .sum for summaries. InTable 2, if a Center includes the product, the extension used in the file’s name is indicated,otherwise a - is indicated.Table 2.Products and Filename Extensions by Analysis CenterCOD EMR ESA GFZ JPL NGS S10.spl orbits . eph .spl - ~.splsp3 orbits . eph .eph .eph - .SP3 .eph .SP3earth orientation .erp .erp . erp .erp .erp - .erpsummary file . sum sum . sum sum sum sum sum.
Precise GPS EphemeridesAll Centers provide GPS satellite ephemerides, although there are some differences in filenameextensions and formats. Five (COD, EMR, ESA, GFZ, and NGS) Centers use .eph as the filenameextension. Of these; four provide files in the sp3 format and one (GFZ) provides the sp 1 format.The other two Centers (.lPL and S10) provide orbit files in both the sp 1 and sp3 formats, and use.sp 1 and .sp3, respectively, as filename extensions. (For a description of these formats, see NOAATechnical Report NOS 133 NGS 46, “Extending the National Geodetic Survey Standard GPS OrbitFormats”, and “NGS Second Generation ASCII and Binary Orbit Formats and AssociatedInterpolation Studies”, both by B. Remondi.)One advantage of the sp3 format is that it allows a field for a clock estimate. Two Centers, CODand EMR, actually fill this field with satellite clock estimates, although their sign conventions areopposite.(However, because of clock dithering implemented as part of Selective Availability, it is a mistaketo think that clock solutions and precise ephemerides should necessarily be reported at the samefrequency. Essentially, GPS orbits are smooth and can be reasonably interpolated given dataspacing at intervals of 15 minutes, or even longer. GPS clock solutions, however, need to besupplied much more frequently (at least every 30 sec.) to derive accurate clock solutions atintermediate points by interpolation.)The sp3 format differs from the sp 1 format also in that it (i) allows an “orbit accuracy exponent”for each satellite, (ii) has an extra digit of precision in its position fields (accurate to 1 mm.), and(iii) allows velocity information as an option (currently exercised by none of the Centers).Given all this, there is little to recommend sp 1 over sp3, except perhaps that the sp 1 format has amuch shorter and easier-to-understand header. The sp 1 format persists most likely because it wasthe first format to gain widespread use and some software was developed around it.Before recommending sp3 as an “official” format, however, we ought to mention realdisadvantages of both it and its sp 1 precursor. Neither allows for exclusion of certain satellitesduring certain times in the file. Thus a Center cannot submit weekly sp3 files if a certain pm wasnot used during one day of the week. Also, because of headers and other adornments, customsoftware must be used (and maintained!) to do what would otherwise be simple operations.For example, it is tedious with these formats to (i) extract results from all Centers for a given prnat a certain time, or (ii) eliminate a certain prn from a file, or even (iii) concatenate files. While itis true that straightforward software can be written to perform these chores, a simpler “basic”format could be used which would rely solely on operating system commands (grep, cat, sortin Unix) for manipulations.An example of a single record from such a format (and all records have the same fields) might be:..e jpl 03199308221215 .0000 -15667.935591 15329.100213 14845 .251566-0.38
Page 1 and 2: ●INTERNATIONAL ASSOCIATION OF GEO
Page 3 and 4: TABLE OF CONTENTS.FINAL AGENDA . .
Page 5 and 6: 13:30 NGS14:00 S1014:30 EMR15:00 CO
Page 7 and 8: LIST OF PARTICIPANTS:Prof. Gerhard
Page 12 and 13: The first field identifies the reco
Page 14 and 15: Summary InformationThe third produc
Page 16 and 17: From Figure 1 we find that there ar
Page 18: to define a reference clock in thei
Page 22 and 23: SESSION 2(IGS orbit products)
Page 24 and 25: 1. introductionThe main objectives
Page 26 and 27: ecause of the above averaging. This
Page 28 and 29: RMS per center (m)o 0 0 0 0 0 oA0Iv
Page 30: Scale (ppb)I I I I I 11+-b~ul0Amo&I
Page 33 and 34: and NGS. Note that the day to day v
Page 35 and 36: Rotation around X-axis (mas)1&0 0o
Page 37 and 38: discussed in Section 3 are here see
Page 39 and 40: -----------------------------------
Page 41 and 42: Residuals in Meters1 1 1 1 1 1 1=%m
Page 43 and 44: Residuals inMeters11111cnficJJw-o A
Page 45 and 46: I I I—Residuals in Meters..—.
Page 47 and 48: 1111ResidualsMeters,—{44
Page 49 and 50: Residuals in MetersI I I II I I IIc
Page 51 and 52: Rms in MetersI 1 ! I 1 10 n0 a0n.ff
Page 53 and 54: IGS- and the COM-sets, but that the
Page 55 and 56: Table 4.1 N.A. Baseline Repeatabili
Page 57 and 58: ..Figure 5.1:Clock solutions for FA
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specifically the preanalysis can be
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discussion, a question as to whethe
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SUMMARY OF SESSION 3This Session be
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IGS POSITION PAPER, IGS ANALYSIS CE
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and Earth orientation parameters (E
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LbPIERS and IGSCentral Bureausand D
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@ IGS will develop instructions, an
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2.2 Analysis Center System DesignFi
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applied to the solution in order to
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..standard deviations. This is conv
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known, the two solutions will be ad
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errors, and can therefore be used a
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International Terrestrial Reference
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Thus, there is the potential of fee
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90” 100” 110” 120” 130” 1
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adiation parameters for each satell
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Bock, Y., R.I. Abbot, C.C. Counselm
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SUMMARY OF SESSION 4This session st
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INTERNATIONAL EARTH ROTATION SERVIC
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x- differences with IERS0.001”I I
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SUMMARY OF SESSION 5In the last ses
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1) I(X3 PROCESSING/REPORTS/FORMATSS
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IGS should foster and encourage reg
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..INTERNATIONAL GPS SERVICE FORGEOD
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ortL.s.4
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1234567a91011121314IsIt17ItIs2C2122
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. Ruth Neilan16S Central BureauJet
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ON1T.>● Jim ZumbergeJet Propulsio
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PROPOSED ORGANIZATION OF THE INTERN
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