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Time Bias Function (TBF) Format
Author: Roger Wood
Reference: SLRMail #0040
Version 1.0 - 1997 January 14
Contents: 1) Introduction
2) Detailed Specification of TBF Standard
3) List of codes of IRV and TBF providers
4) List of satellite names used in TBF files
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 of 1999 May)
ATS AlliedSignal Technical Services Corporation, USA
CSR Center for Space Research, University of Texas, USA
GFZ GeoForschungsZentrum, Germany
MCC Mission Control Centre, Russia
RGO NERC Satellite Laser Ranger Facility, UK
Note: Here is a complete list of providers.
4) List of satellite names used in TBF files (as of 1999 May)
Adeos Ajisai ERS1 ERS2 Etalon1 Etalon2
Fizeau GFO1 GFZ1 Glonass62 GlonassXX GPS35
GPS36 Lageos1 Lageos2 Norton Ralph Resurs
Starlette Stella Sunsat Topex Westpac
Note: All the Glonass satellites were not listed due to their sheer number,
the general satellite name for each Glonass will be GlonassXX where XX is a
2-digit number assinged by the ILRS
Note: Here is a complete list of satellite missions.
5) Distribution and frequency
Collection and collation of TBFs from different providers will be
carried out by the NERC 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 and WWW 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 NERC
(every hour if new data have been processed). These TBF files are also
archived at the CDDIS.
Site Internet Address Directory Filename
(1997 Jan 14)
EDC: 129.187.165.3 pub/laser/timebias tbf_std_9701.14
dgfi3.dgfi.badw-muenchen.de
NERC: 192.171.155.28 nercslr/current tbf_std_9701.14
mtfiles.nerc-monkswood.ac.uk
CDDIS: 128.183.204.168 pub/reports/slrtbf tbf_std_970114
cddisa.gsfc.nsa.gov
Site WWW address:
EDC: ftp://ftp.dgfi.badw-muenchen.de/pub/laser/timebias/
NERC: ftp://mtfiles.nerc-monkswood.ac.uk/nercslr/current/
CDDIS: ftp://cddis.gsfc.nasa.gov/reports/slrtbf/
7) Other files stored at EDC and NERC
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 1999 05 06 13 50 Ver1.0
! ----------------------------------------------------------------------------
ERS1 6177 GFZ334 GFZ 1999 05 05 51297 7.4 0.00 2.790 0.000
ERS2 6178 GFZ170 GFZ 1999 05 06 51302 0.0 -1.20 1.904 0.000
GFZ1 8001 GFZ544 GFZ 1999 05 05 51303 0.0 0.00 0.000 0.000
Ajisai 1500 ATS087 RGO 1999 05 06 51301 -104.0 -9.32 0.123 0.000
Ajisai 1500 RGO065 RGO 1999 05 06 51301 -40.3 -4.28 -0.112 0.000
Etalon1 525 CSR009 RGO 1999 05 04 51297 -232.9 -16.87 0.000 0.000 27.9 567.6
Etalon2 4146 CSR009 RGO 1999 05 05 51298 680.9 -74.61 0.000 0.000 27.9 567.6
GFO1 8501 ATS042 RGO 1999 05 06 51301 128.4 55.44 9.873 0.204
GFO1 8501 RGO012 RGO 1999 05 06 51301 4191.8 239.43 10.244 0.000
GPS35 3535 ATS084 RGO 1999 05 06 51299 173.3 16.55 0.654 0.000
GPS36 3636 ATS074 RGO 1999 05 06 51299 337.5 5.66 -0.012 0.000
Glonass62 9062 ATS006 RGO 1999 05 05 51298 147.1 -6.73 0.000 0.000
Glonass65 3027 RGO023 RGO 1999 03 31 51268 0.0 0.00 0.000 0.000
Glonass66 9066 ATS035 RGO 1999 05 06 51299 80.5 2.04 0.000 0.000
Glonass67 9067 RGO025 RGO 1999 05 02 51295 1135.0 82.99 2.235 0.000
Glonass68 9068 ATS007 RGO 1999 05 05 51299 -99.3 -18.99 0.000 0.000
Glonass69 9069 ATS009 RGO 1999 05 06 51300 36.9 -3.57 0.000 0.000
Glonass70 9070 ATS007 RGO 1999 05 06 51300 4.5 -2.38 0.000 0.000
Glonass71 9071 ATS014 RGO 1999 05 05 51298 -147.8 -11.49 0.000 0.000
Glonass71 9071 RGO011 RGO 1999 05 05 51298 -28.7 -1.92 0.000 0.000
Glonass72 9072 ATS008 RGO 1999 05 06 51299 12.4 8.98 0.000 0.000
Glonass79 9079 ATS007 RGO 1999 05 06 51299 -14.5 1.78 0.000 0.000
Lageos1 1155 CSR029 RGO 1999 05 06 51301 -318.3 -2.52 0.013 0.000 229.3 567.6
Lageos2 5986 CSR005 RGO 1999 05 06 51299 351.6 2.57 0.031 0.000 229.3 567.6
Starlette 1134 ATS126 RGO 1999 05 06 51301 2.5 2.87 0.000 0.000
Starlette 1134 RGO072 RGO 1999 05 06 51301 -164.3 -19.90 -0.632 -0.063
Stella 643 ATS054 RGO 1999 05 06 51301 3.5 3.02 0.000 0.000
Stella 643 RGO072 RGO 1999 05 06 51301 -144.6 -20.66 -0.356 0.000
Sunsat 2301 ATS004 RGO 1999 04 30 51298 0.0 0.00 0.000 0.000
Topex 4377 ATS118 RGO 1999 05 06 51301 10.8 7.04 2.116 0.000
Topex 4377 RGO108 RGO 1999 05 06 51301 -435.4 -47.91 -0.028 0.156
Westpac 8801 MCC054 RGO 1999 05 06 51304 0.0 0.00 0.000 0.000
! End of file
Responsible Government Official:
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