From jimr@maia.usno.navy.mil Fri Jul 10 12:23:45 EDT 1998 Received: (from jimr@localhost) by maia.usno.navy.mil (8.7.5/8.7.3) id MAA14257 for gpst@maia; Fri, 10 Jul 1998 12:14:50 -0400 (EDT) From: Jim Ray (USNO 202-762-1444)Message-Id: <199807101614.MAA14257@maia.usno.navy.mil> Subject: proposed format to exchange clock data To: gpst@maia.usno.navy.mil Date: Fri, 10 Jul 1998 12:14:50 EDT X-Mailer: Elm [revision: 212.4] Status: RO Dear Colleagues, Below is a draft format which I propose for the exchange of a variety of clock data. As explained in the introduction, the IGS has a pressing need for such an exchange format for its analysis products. This draft format is the result of considerable discussion among the IGS Analysis Centers and draws upon contributions from a number of individuals, which I very gratefully acknowledge and appreciate. It would obviously be useful if the same format can be used to exchange other clock-like information that will be necessary during the course of this Pilot Project. Therefore, I ask that you all please examine this format and let me know at your earliest opportunity if you have suggested improvements. In particular, it would be helpful to know of omissions or other limitations that might adversely affect the work of the Pilot Project. I propose that we try to adopt an initial version by 01 August, preferably, so that exchange of clock data can commence soon. It will undoubtedly be necessary to make later refinements but backwards compatibility would be highly desirable. Best regards, --Jim Proposed RINEX Extensions to Handle Clock Information ***************************************************** (draft 10 July 1998) 0. INTRODUCTION Previously, the IGS currently has produced clock results only for the GPS satellites and these are tabulated and distributed at the 15-minute intervals used in the sp3 orbit ephemerides files. There is a much interest in increasing the satellite clock interval to 30-seconds (to overcome SA effects on interpolation) and also in producing station clock results (at some appropriate interval, probably 5 minutes). In principle, the sp3 format could continue to be used for both of these extensions, but it would be wasteful considering that the vast majority of the file space is set aside for orbit information. Also, the variety of other clock information that also needs to be exchanged does not lend itself to the sp3 format. Alternatively, the IGS could devise a new format specifically for distributing clock information. It does not appear that the timing community already uses a standard data format that is well suited for the IGS needs. 1. CLOCK DATA TYPES At the level of monitoring and reporting data from a specific GPS station the following types of observations can be expected: calibration data (C): time delay measurements between a GPS receiver and some external reference point (e.g., local master clock) discontinuity data (D): a phase-tracking GPS receiver (e.g., AOA TurboRogue) maintains an internal clock that sometimes will reset itself; in principle, there may be methods to monitor such changes which could then be logged as a relative change in clock state >From analysis of GPS data, the results for an ensemble of station and satellite clocks can be determined differentially. Normally, all clock values are estimated relative to a single clock being held fixed as a reference. Alternatively, a linear combination of the estimated clocks can be held fixed to some apriori value (normally, zero). In any case, the data are: analysis data (A): results from GPS phase/pseudorange data analysis for a network of stations and satellite, all relative to a fixed reference adopted in the analysis In addition, the broadcast clocks of the satellites can be monitored and compared to a laboratory standard: monitor data (M): broadcast values for satellite clocks as compared with laboratory standard via monitor receivers (usually timing receivers) 2. FORMAT TYPES AND FILE NAMING Following established practice, the station-specific data ("C" and "D") could be reported using an extension of the RINEX format while the analysis data ("A" and "M") could be reported using an extension to a standard product format, such as SINEX. However, since all of these data types are related and probably need similar format requirements, it seems more economical to consider a single file format type suitable for all. RINEX seems the most appropriate file type, even though it is not normally used for analysis products. When it becomes feasible and necessary to include clock estimates with other analysis products, then suitable formats can be incorporated into SINEX. Until then, it is suggested that a RINEX format extension be used for all clock/timing results. Normally, "C" and "D" data types would be collected at the stations, files would be prepared at the data centers, and the files would flow to the Global Data Centers named as: for calibration data (C) & discontinuity data (D) ------------------------------------------------- ssssdddf.yyC ssss: 4-character station name designator ddd: day of the year of first record f: file sequence number within day 0: file contains all the existing data of the current day yy: year C: file type "C" for clock information The suffix "C" would be a new RINEX file type. Normally, data would be compiled into files by each 24-hour day (GPS time). The analysis results "A" and "M" would be formed at IGS Analysis Centers or by IGS/BIPM Pilot Project analysis groups and would normally include results for a number of stations and/or satellites. These files would be named as: for analysis data (A) & monitor data (M) ---------------------------------------- cccwwwwd.clk ccc: 3-character analysis center name designator wwww: GPS week number d: day within GPS week (0 - 7) clk: suffix to identify clock information product files Files could be either daily (d = 0,...,6) or weekly (d = 7). However, despite the file names, a single format for the contents would apply for all data types. 3. NUMERICAL PRECISION In order to maintain adequate precision, Fortran E format is used for all clock quantities, rather than F format. All timing quantities can be reported with up to the full precision of REAL*8 numerical precision, about 16 decimal places. 4. CLOCK DISCONTINUITIES Clock discontinuities (in bias, rate, and/or acceleration) could be reported in either of two ways. If monitored in situ and logged, these could be reported as "D" data types in .yyC station files. If detected in data analysis, these can be reported in .clk files as two "A" data records for the same station at the same epoch but with two different sets of clock values. 5. RECEIVER AND SATELLITE NAMES Since the clock data are normally used in conjunction with data analysis results (even for the calibration and discontinuity data types), it is most convenient to use naming conventions for the receivers and satellites which correspond to the same names used in analyses. In order to ensure uniqueness and complete identification, it is also necesssary to supply the station ID number (usually, the DOMES number issued by the Terrestrial Frame Section of the IERS). Thus, receivers should be identified by: Station names: IGS official 4-character station name designator Station number: DOMES number (or other unique identifier) For satellite names, the following designations are used in RINEX: Satellite names: 3-character string: "Gnn": nn is the PRN number for GPS satellites "Rnn": nn is the almanac number for GLONASS satellites 6. RINEX CLOCK FORMAT DEFINITIONS AND EXAMPLES The header recorders should be included in the order indicated, when required. The records below marked with * are optional. It is recommended that each record be read into a blank buffer string and then the information can be decoded afterwards from the buffer. Header records are limited to 80 characters. Data records are also limited to 80 characters when only clock bias (and sigma) data are provided; however, the data records can extend up to 170 characters if the optional clock rate and acceleration (and sigmas) data are also transmitted. A data file must begin with the header records. Data records begin immediately after the "END OF HEADER" record and complete the remainder of the data file. +----------------------------------------------------------------------------+ | TABLE A15 | | CLOCK DATA FILE - HEADER SECTION DESCRIPTION | +--------------------+------------------------------------------+------------+ | HEADER LABEL | DESCRIPTION | FORMAT | | (Columns 61-80) | | | +--------------------+------------------------------------------+------------+ |RINEX VERSION / TYPE| - Format version (2.00) | F9.2,11X, | | | - File type ("C" for Clock Data) | A1,39X | +--------------------+------------------------------------------+------------+ |PGM / RUN BY / DATE | - Name of program creating current file | A20, | | | - Name of agency creating current file | A20, | | | - Date of file creation | A20 | +--------------------+------------------------------------------+------------+ *|COMMENT | Comment line(s) | A60 |* +--------------------+------------------------------------------+------------+ *|LEAP SECONDS | Number of leap seconds since 6-Jan-1980 | I6 |* | | Recommended as an aid to convert from | | | | GPS time to UTC | | +--------------------+------------------------------------------+------------+ |# / TYPES OF DATA | - Number of different clock data types | I6, | | | stored in the file | | | | - List of clock data types | 4(5X,A1) | | | | | | | The following clock data types are | | | | defined in RINEX Version 2: | | | | | | | | "A" : Data analysis results for set of | | | | network receivers and satellites | | | | wrt to reference clock fixed in | | | | the analysis | | | | "C" : Calibration measurements for a | | | | single GPS receiver wrt an | | | | external local reference clock | | | | "D" : Discontinuity measurements for a | | | | single GPS receiver | | | | "M" : Monitor measurements for the | | | | broadcast satellite clocks wrt a | | | | standard timescale | | | | | | +--------------------+------------------------------------------+------------+ |STATION NAME / NUMB | - 4-character station name designator | A4,1X, | | | - Unique station identifier, | A20,35X | | | preferably the DOMES number | | | | | | | | * REQUIRED for data types "C" & "D" | | | | | | +--------------------+------------------------------------------+------------+ |STATION CLK REF | Unique identifier for external | A60 | | | reference clock being used as the | | | | standard for calibration | | | | | | | | * REQUIRED for data type "C" | | | | | | +--------------------+------------------------------------------+------------+ |ANALYSIS CENTER | Name of Analysis Center | | | | - 3-character IGS AC designator | A3,2X, | | | - Full name of Analysis Center | A55 | | | | | | | * REQUIRED for data types "A" & "M" | | | | | | +--------------------+------------------------------------------+------------+ |ANALYSIS CLK REF | - Name of the receiver or satellite | A5,1X, | | | used as the fixed reference in data | | | | analysis | | | | - Unique station identifier for | A20 | | | reference clock (if a receiver), | | | | preferably the DOMES number | | | | | | | | OR | | | | | | | | If the reference clock is "NETWK", then | | | | a sum of receiver & satellite clocks | | | | was constrained to an apriori value | | | | (usually, zero) as the reference in the | | | | data analysis. In this case, the next | | | | record(s) must list the clocks used in | | | | the reference combination constraint. | | | | | | | | For the case of "NETWK" reference, this | | | | record has the following format: | | | | | | | | - Name of the reference ("NETWK") | A5,1X, | | | - Number of clocks used in the | I20, | | | reference combination constraint | | | | (listed in the next records) | | | | - Optionally a non-zero value for the | 5X,E22.16 | | | the apriori clock constraint can be | | | | provided. | | | | | | | | * REQUIRED for data types "A" | | | | | | +--------------------+------------------------------------------+------------+ |ANALYSIS CLK REF NET| Names of the receivers or satellites | 12(A4,1X) | | | included in the linear combination used | | | | as the fixed reference in data analysis | | | | | | | | As many records as necessary may be | | | | included to complete the list | | | | | | | | * REQUIRED if "ANALYSIS CLK REF" is | | | | "NETWK" | | | | | | +--------------------+------------------------------------------+------------+ |STATION LIST / TRF | - Number of stations included in the | I6,1X | | | clock data records and listed in | | | | following header records | | | | - Terrestrial reference frame or | A53 | | | SINEX solution for the station | | | | coordinates which match the clock | | | | solution | | | | | | | | * REQUIRED for data types "A" | | | | | | +--------------------+------------------------------------------+------------+ |SOLN STA NAMES/NOS | For each station included in the clock | | | | data records (number given in the | | | | previous header record), include one | | | | record with the following information: | | | | - 4-character station name designator | A4,1X, | | | - Unique station identifier, | A20,35X | | | preferably the DOMES number | | | | | | | | * REQUIRED for data types "A" | | | | | | +--------------------+------------------------------------------+------------+ |END OF HEADER | Last record in the header section. | 60X | +--------------------+------------------------------------------+------------+ +----------------------------------------------------------------------------+ | TABLE A16 | | CLOCK DATA FILE - DATA RECORD DESCRIPTION | | | | (EACH RECORD CAN EXTEND UP TO 170 CHARACTERS IN LENGTH) | +-------------+-------------------------------------------------+------------+ | OBS. RECORD | DESCRIPTION | FORMAT | +-------------+-------------------------------------------------+------------+ |TYP/EPOCH/CLK| - Clock data type (A, C, D, M) | A1,1X, | | | | | | | - Receiver or satellite name | A4,1X, | | | - Receiver name is the IGS 4-character | | | | designator | | | | - Satellite name is a 5-character string: | | | | - "Gnn" where nn is the PRN number | | | | for GPS satellite | | | | - "Rnn" where nn is the almanac number | | | | for GLONASS satellite | | | | | | | | - Epoch in GPS time (not local time!): | | | | year (4 digits),month,day,hour,min,sec | I4,4I3, | | | second | F10.6, | | | | | | | - Clock data in the following sequence: | | | | - Clock bias (seconds) | X,E22.16, | | | - Clock bias sigma [optional] (seconds) | X,E22.16, | | | - Clock rate [optional] (dimensionless) | X,E22.16, | | | - Clock rate sigma [optional] (dimensionless)| X,E22.16, | | | - Clock acceleration [optional] (per second) | X,E22.16, | | | - Clock acceleration sigma [optional] | X,E22.16 | | | (per second) | | | | | | | | NB: For data types "A", "C", and "M", | | | | clock data are in the sense of | | | | reported station/satellite clock | | | | *minus* reference clock value. | | | | For data type "D", clock data are | | | | the sense of clock value after | | | | discontinuity *minus* before. | | | | | | | | Clock data apart from bias values are | | | | optional. However, if any optional values | | | | are included, then all lower order values | | | | must be supplied even if optional (although | | | | zero values may be given) | | | | | | +-------------+-------------------------------------------------+------------+ +------------------------------------------------------------------------------+ | TABLE A17 | | CLOCK DATA FILE - EXAMPLE FOR ANALYSIS DATA | +------------------------------------------------------------------------------+ ----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8| 2.00 CLOCK DATA RINEX VERSION / TYPE TORINEXC V9.9 USNO 3-APR-96 00:10 PGM / RUN BY / DATE EXAMPLE OF A CLOCK DATA FILE COMMENT IN THIS CASE ANALYSIS RESULTS ARE INCLUDED COMMENT 10 LEAP SECONDS 1 A # / TYPES OF DATA USN USNO USING GIPSY/OASIS-II ANALYSIS CENTER USNO 40451S003 ANALYSIS CLK REF 4 ITRF96 STATION LIST / TRF GOLD 40405S031 SOLN STA NAMES/NOS AREQ 42202M005 SOLN STA NAMES/NOS TIDB 50103M108 SOLN STA NAMES/NOS HARK 30302M007 SOLN STA NAMES/NOS END OF HEADER A AREQ 1994 07 14 20 59 50.000000 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 A G16 1994 07 14 20 59 50.000000 -.1234567890123456E-06 .1234567890123456E-06 -.1234567890123456E-06 .1234567890123456E-06 -.1234567890123456E-06 .1234567890123456E-06 A GOLD 1994 07 14 20 59 50.000000 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 A HARK 1994 07 14 20 59 50.000000 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 A TIDB 1994 07 14 20 59 50.000000 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 .1234567890123456E-06 ----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8| +------------------------------------------------------------------------------+ | TABLE A18 | | CLOCK DATA FILE - EXAMPLE FOR CALIBRATION/DISCONTINUITY DATA | +------------------------------------------------------------------------------+ ----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8| 2.00 CLOCK DATA RINEX VERSION / TYPE TORINEXC V9.9 USNO 3-APR-96 00:10 PGM / RUN BY / DATE EXAMPLE OF A CLOCK DATA FILE COMMENT IN THIS CASE CALIBRATION/DISCONTINUITY DATA GIVEN COMMENT 10 LEAP SECONDS 2 C D # / TYPES OF DATA USNO 40451S003 STATION NAME / NUMB UTC(USNO) MASTER CLOCK VIA CONTINUOUS CABLE MONITOR STATION CLK REF END OF HEADER C USNO 1994 07 14 20 59 50.000000 .1234567890123456E-06 .1234567890123456E-06 C USNO 1994 07 14 22 19 30.000000 -.1234567890123456E-06 .1234567890123456E-06 D USNO 1994 07 14 22 23 14.500000 -.1234567890123456E-06 .1234567890123456E-06 C USNO 1994 07 14 23 44 50.000000 -.1234567890123456E-06 .1234567890123456E-06 ----|---1|0---|---2|0---|---3|0---|---4|0---|---5|0---|---6|0---|---7|0---|---8|