| Date: | 1997-01-14 20:00:00 | |
| Sender: | Roger Wood, SLR Herstmonceux (for Time Bias Function Working Group) <rw@gxvf.rgo.ac.uk (Roger Wood, SLR Herstmonceux)> | |
| Subject: | [SLR-Mail] No. 40: A new standard for time bias function distribution | |
| Author: | Roger Wood, SLR Herstmonceux | |
| Content: | ******************************************************************************** SLR Electronic Mail 1997-01-14 20:00:00 UTC Message No. 40 ******************************************************************************** Author: Roger Wood, SLR Herstmonceux (for Time Bias Function Working Group) Subject: A new standard for time bias function distribution Announcement ------------ The message which follows gives a detailed specification for standard time bias functions (TBFs) drawn up by the CSTG Time Bias Working Group. From 1997 January 20 TBFs will be distributed via the European Data Centre to a new mailing list called SLRTBF. Initially it will be a copy of SLRmail so as to ensure the widest global coverage. Anyone on the SLRmail list with no interest in receiving TBFs should please send a blank message with the subject header ”unsubscribe” to slrtbf@dgfi.badw-muenchen.de when their entry will be removed from the slrtbf list. To join the list use the subject header ”subscribe”. It is intended that this distribution will collect and collate all TBFs currently produced by different providers and mail them as a single file (see example file at the end of the specification) at least once per day. From January 20 the new scheme will work in parallel with present distributions for a trial period of about a month. If all is running smoothly at the end of that period, the existing distributions will be discontinued. A further announcement will be made at that time. All comments about the new files and the distribution are welcomed and should be sent to Roger Wood at Herstmonceux (rw@gxvf.ego.ac.uk). ====================================================================== FORMAT SPECIFICATION FOR TIMEBIAS FUNCTION FILES Version 1.0 - 1997 January 14 Contents: 1) Introduction 2) Detailed Specification of TBF Standard 3) List of codes of IRV and TBF providers (at 1997 Jan) 4) List of satellite names used in TBF files (at 1997 Jan) 5) Distribution and frequency 6) FTP access to TBF data 7) Other files stored at EDC and RGOC 8) Updating policy 9) Example of Standard TBF file 1) Introduction: ------------ A time bias function (TBF) is a simple, low order polynomial which characterises the way in which the real along-track motion of a satellite departs from an orbit prediction based on previous ranging data. Thus an orbit prediction together with a well-determined TBF enables an observing station to approximate the true motion of the satellite very closely, thereby improving acquisition and tracking. This format specification is based on a function which gives the time bias TB (measured in milliseconds) at epoch T (the Modified Julian Date, measured in days and decimals of a day) according to the following formula: TB = a + b(T-T0) + c(T-T0)**2 + d(T-T0)**3 where a, b, c, d are polynomial coefficients; and T0 is the zero point epoch of the TBF (MJD). For satellites with long-term predictions provided by the Center for Space Research (Lageoses and Etalons) two files of long-term extrapolations of Earth rotation were adopted and distributed with the predictions. Stations using these predictions remove the CSR-adopted Earth rotation at epoch T and replace it with the ”true” Earth rotation extrapolated from data published in the most recent IERS Bulletin A. Insertion or removal of leap seconds is included in the CSR Earth rotation file and reflected in the IRVs. For convenience the UT1-UTC corrections adopted by CSR and that derived from IERS data are included on the DATA lines of these four satellites. 2) Detailed Specification of TBF Standard: -------------------------------------- Three types of lines are defined: TITLE, COMMENT and DATA. Only DATA lines do not have ”!” in column 1. The TITLE line is always the first line and contains information that a station may want to process in order to decide whether or not to adopt the contents. Other COMMENT lines will contain information of occasional interest drawing attention to some feature of the file, e.g. the fact that Topex has been manoeuvred without prior notice and the TBF (with respect to an unchanged IRV set) has changed slope drastically. TITLE line Cols 2,11,16,21,32-33,37-38,43,46,49,52,55-56,63-end are always blank. Col 1 An exclamation mark, ”!”. Cols 3-31 The string ”Standard Time Bias Functions:” Cols 34-36 A 3-character identifier indicating the organisation which collated this TBF file, e.g. ”RGO”. See section 3 below for a complete list of current providers. Cols 39-54 Date (yyyy mm dd) and time (hh mm UT) at which this file was generated, e.g. ”1997 01 14 12 34”. Cols 57-62 Version number for the format (1.0 to start with; minor changes indicated by the decimal; major changes by the integer), e.g. ”Ver1.0”. Example: ! Standard Time Bias Functions: RGO 1997 01 14 12 34 Ver1.0 COMMENT lines Col 2 is always blank. Col 1 An exclamation mark, ”!”. Cols 3-80 Character string giving information about some aspect of the file. Examples: ! Topex: slope of TB function increased sharply at MJD 50432.667 ! GFZ1: REMEMBER all function values have had DRAG correction REMOVED DATA lines Each data line contains a complete TBF for one satellite with respect to the IRVs from the provider indicated in the ”IRV source reference” field. The data items on each line are: Cols 11,16,23,27,32,35,38,44,52,61,70,77,84 are always blank. Cols 1-10 Satellite name without spaces, hyphens or underscores, e.g. ”Lageos1 ”. The name is left-justified and blank filled to 10 characters. See section 4 below for a complete list of satellite names. Cols 12-15 NASA´s 4-digit Support Identification Code number, as used in standard IRV sets, e.g. ”1155” for Lageos 1. Cols 17-19 IRV source reference, a 3-character identifier indicating who produced the IRVs used to compute the TBF, e.g. ”ATS” for ATSC. See section 3 below for a complete list of IRV provider codes. Cols 20-22 IRV set number, a 3-digit number uniquely identifying the set of IRVs used to compute the TBF. In IRV sets this number appears on the third line of the 4 lines of data which define IRVs for a given interval (usually 1 day). Cols 24-26 TBF source reference, a 3-character identifier indicating who computed this TBF. See section 3 below for the list of IRV provider codes. Cols 28-37 Calendar date that the TBF was generated in the format yyyy mm dd, e.g. ”1997 01 14”. Cols 39-43 Modified Julian Date which is the zero point of the TBF, i.e. full Julian Date - 2400000.5, e.g. ”50438”, unit = days. NB full days only, 00:00 UT implied. Cols 45-51 Coefficient a of TBF, e.g. ”-1234.5”, format fixed, unit = milliseconds. Cols 53-60 Coefficient b of TBF, e.g. ”-1234.56”, format fixed. unit = milliseconds/day. Cols 62-69 Coefficient c of TBF, e.g. ”-123.456”, format fixed. unit = milliseconds/day**2. Cols 71-76 Coefficient d of TBF, e.g. ”-1.234”, format fixed. unit = milliseconds/day**3. For the Lageos and Etalon satellites only (see introduction): Cols 78-83 UT1-UTC correction used in the production of the CSR IRVs, e.g. ”-586.1”, format fixed, unit = milliseconds. Cols 85-90 UT1-UTC correction derived from the IERS Bulletin, e.g. ”-123.4”, unit = milliseconds. Example: Starlette 1134 RGO052 RGO 1997 01 14 50438 -0.9 1.34 0.184 0.000 3) List of codes of IRV and TBF providers (as at 1997 January) -------------------------------------- ATS AlliedSignal Technical Services Corporation, USA CSR Center for Space Research, University of Texas, USA GFZ GeoForschungsZentrum, Germany NSD National Space Development Agency, Japan RGO Royal Greenwich Observatory, UK 4) List of satellite names used in TBF files (as at 1997 January) ----------------------------------------- Adeos Ajisai ERS2 Etalon1 Etalon2 Fizeau GFZ1 Glonass63 Glonass67 GPS35 GPS36 Lageos1 Lageos2 Norton Ralph Resurs Starlette Stella Topex 5) Distribution and frequency -------------------------- Collection and collation of TBFs from different providers will be carried out by the SLR group at Herstmonceux. Distribution to the global community will be made from DGFI in Munich using the EDC email exploder to a dedicated address list (based initially on SLRmail) called SLRTBF starting on 1997 January 20. If you wish to be removed from the list send a blank message with the subject ”unsubscribe” to slrtbf@dgfi.badw-muenchen.de To join the list send a blank message with the subject ”subscribe”. For most satellites once per day updating of TBFs gives extrapolations accurate to a few milliseconds. This requirement will be met by regular mailings of the standard TBF at about 1600 UT each day. In addition there will be irregular mailings to get the best possible information for satellite manoeuvres and for difficult targets such as GFZ-1 and TiPS. In all cases the complete TBF file will be mailed (including any updates which may have been made for other satellites) and recipients may assume that all the functions contained in any message are the best currently available. 6) FTP access to TBF data ---------------------- As well as distribution by email, TBF files are simultaneously deposited in anonymous FTP accounts at EDC (whenever files are sent out) and at RGO Cambridge (every hour if new data have been processed). Site Address Directory Filename (1997 Jan 14) EDC: 129.187.165.3 pub/laser/timebias tbf_std_9701.14 dgfi3.dgfi.badw-muenchen.de RGOC: 131.111.69.186 pub/slrirv/current tbf_std_9701.14 cass41.ast.cam.ac.uk 7) Other files stored at EDC and RGOC ---------------------------------- tbf_std_spec_ver1.0 This document: TBF specification version 1.0 tbf_irv_providers.lst List of IRV providers + codes in TBF files tbf_satellite_names.lst List of full satellite names in TBF files 8) Updating policy --------------- Every effort has been made to include in the present format specification all the information which is required for effective use of TBFs. Any changes which are found to be desirable will, as far as possible, be implemented so as to be compatible with previous versions. No changes will be made without an announcement via SLRmail of the details and the date of implementation. Changes in the frequency of distribution may be made without announcement in the light of experience during operation and in response to circumstances, such as the launch of a new target. Similarly changes in the lists of IRV providers and of satellites will not be announced but will be reflected quickly in the files held at EDC and RGOC. 9) Example of Standard TBF file ---------------------------- ! Standard Time Bias Functions: RGO 1997 01 14 17 45 Ver1.0 ! Example of Time Bias Function file in the agreed standard format ! +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ! Trial of Standard Time Bias Function distribution (~1 month from 1997 Jan 20) ! Email comments/complaints to Roger Wood (rw@gxvf.rgo.ac.uk) ! Email slrtbf@dgfi.badw-muenchen.de with subject ”unsubscribe” to have your ! address removed from the mailing list ! +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ! GFZ1: REMEMBER all function values have had DRAG correction REMOVED Adeos 1555 NSD061 RGO 1997 01 14 50461 0.3 0.00 0.000 0.000 Adeos 1555 NSD061 NSD 1997 01 14 50462 0.0 0.00 0.000 0.000 Ajisai 1500 RGO039 RGO 1997 01 14 50457 -2.9 -0.68 -0.078 0.000 ERS2 6178 GFZ065 RGO 1997 01 14 50462 0.2 0.00 0.000 0.000 ERS2 6178 GFZ065 GFZ 1997 01 14 50462 0.0 0.00 0.000 0.000 Etalon1 525 CSR008 RGO 1997 01 14 50429 -53.9 -0.98 0.000 0.000 -137.8 -229.8 Etalon2 4146 CSR008 RGO 1997 01 14 50452 24.2 -0.21 0.000 0.000 -137.8 -229.8 Fizeau 5050 ATS047 RGO 1997 01 14 50461 6.2 3.87 0.000 0.000 GFZ1 8001 GFZ176 RGO 1997 01 14 50462 0.0 0.00 0.000 0.000 GFZ1 8001 GFZ176 GFZ 1997 01 14 50462 0.0 0.00 0.000 0.000 Glonass63 6363 RGO010 RGO 1997 01 14 50453 -10.4 -1.55 0.000 0.000 Glonass67 6767 RGO010 RGO 1997 01 14 50452 -80.8 -0.53 0.000 0.000 GPS35 3535 RGO020 RGO 1997 01 14 50460 -20.9 -4.56 0.000 0.000 GPS35 3535 ATS047 RGO 1997 01 14 50452 -245.5 -29.31 -0.986 0.000 GPS36 3636 RGO021 RGO 1997 01 14 50460 -2.2 -4.44 0.000 0.000 GPS36 3636 ATS040 RGO 1997 01 14 50458 167.4 -15.63 -2.018 0.000 Lageos1 1155 CSR027 RGO 1997 01 14 50452 -4.4 -1.03 -0.013 0.000 -137.8 -225.2 Lageos2 5986 CSR003 RGO 1997 01 14 50452 35.3 0.80 0.002 0.000 -137.8 -225.2 Norton 6001 ATS056 RGO 1997 01 14 50454 -141.1 106.91 0.000 0.000 Ralph 6002 ATS056 RGO 1997 01 14 50454 -160.8 0.00 0.000 0.000 Resurs 1333 ATS025 RGO 1997 01 14 50455 0.0 0.00 0.000 0.000 Stella 643 RGO050 RGO 1997 01 14 50459 -0.2 -0.16 0.000 0.000 Starlette 1134 RGO053 RGO 1997 01 14 50457 -1.9 -0.26 0.000 0.000 Topex 4377 RGO072 RGO 1997 01 14 50457 19.1 7.50 0.841 0.016 ======================================================================= Roger Wood, NERC Satellite Laser Ranger Facility, Herstmonceux Castle Hailsham, East Sussex, UK BN27 1RP Tel: +44 (01323) 833888 Fax: +44 (01323) 833929 Email: rw@gxvf.rgo.ac.uk ======================================================================= From: rw@gxvf.rgo.ac.uk (Roger Wood, SLR Herstmonceux) ******************************************************************************** |