PDS_VERSION_ID = PDS3 RECORD_TYPE = STREAM DATA_SET_ID = "RO-C-RSI-1/2/3-ESC2-0851-V1.0" PRODUCT_ID = "TRK-2-21" PRODUCT_CREATION_TIME = 2017-09-26T09:36:47.000 OBJECT = TEXT PUBLICATION_DATE = 1997-08-04 NOTE = "Software Interface Specification for the JPL DSN TSAC Universal Time and Polar Motion (UTPM) file and the TEMPO Earth Orientation Parameters (EOP) file. Adapted from the HTML file at URL http://epic.jpl.nasa.gov/nav/eop/trk-2-21.html Formatted for display or printing at 58 lines per page with up to 78 constant width characters per line." END_OBJECT = TEXT END TRK-2-21 EOP Data Interface DSN SYSTEMS REQUIREMENTS DETAILED INTERFACE DESIGN DOCUMENT 820-13; Rev. A TRK-2-21 DSN TRACKING SYSTEM INTERFACES EARTH-ORIENTATION PARAMETER DATA INTERFACE CONTENTS PURPOSE REVISION AND CONTROL GENERAL INFORMATION UTPM STOIC DATA FORMAT STOIC data file with seconds past 2000 time tags STOIC data file with seconds past 1950 time tags EOP DATA FORMAT Sample EOP file GLOSSARY PURPOSE This module defines the data format and content of the Earth-Orientation Parameter (EOP) files and the Universal Time and Polar Motion (UTPM) files received from the Tracking System Analytic Calibration (TSAC) group.(NOTE: These files are now produced by the Time and Earth Motion Precision Observation (TEMPO) group.) REVISION AND CONTROL Revisions or changes to the information herein presented may be initiated in accordance with the procedures in Section I of this document. GENERAL INFORMATION The DSN and flight projects use EOP data, which includes UTPM data, in the process of performing orbit determination and generating prediction data. These data are to be provided at intervals determined by the user's accuracy requirements and as negotiated with the various DSN and project users. Two different file formats are described in this interface document. The first kind of file contains Universal Time and Polar Motion (UTPM) data only, and has the same format as was described in the previous version of TRK-2-21. It will be referred to hereafter as the UTPM STOIC file; in the past, such files have also been called TPOLY files or TP arrays. The second kind of file contains UTPM data and, in addition, nutation correction parameters necessary to determine inertial station locations at the few-cm level. It will be referred to as the EOP file. For a detailed explanation of the models underlying this file, and how the file is used, see Folkner et al., "Earth Orientation Parameter (EOP) file description and usage," JPL IOM 335.1-11-93, May 21, 1993. The data are deliverable via electrical interface. UTPM STOIC DATA FORMAT UTPM STOIC data are available as ASCII files in Fortran Namelist format. The data file consists of 88 card-image records. In Fortran Namelist format, each variable in a single record is of the form variable(i) = value(i), value(i+1), value(i+2)...value(i+j-1), where i is an index running from 1 to 335 and j is the number of data values of the variable given on a single record. The subscripts i+1 through i+j are not given explicitly. Two different UTPM STOIC files are available, identical except for the time tags, generally referred to as "seconds past 2000" or "seconds past 1950" (see TIME below). All time rates of change are with respect to International Atomic Time (TAI). Specific inputs are as follows: First record: TIMPOL A label giving the date of the last input datum (LD) and the last date for which predictions are given, typically 30 days after the file is generated (PT). For Univac deliveries, the LD/PT portion names the Univac element. (See Figures TRK-2-21-1 and TRK-2-21-2 for LD and PT locations.) For UTPM STOIC files created since 1 May 1993, a variable called UT1TYP has been placed at the end of TIMPOL. Only two values are allowed, either UT1TYP=UT1R or UT1TYP=UT1. Older UTPM STOIC files are all UT1R unless the string UT1 tidal terms appears at the end of TIMPOL. See the UT1R discussion in the Glossary. Format: 16A4 (VAX 32-bit words) or 11A6 (Univac 36-bit words) Records 2-14: IT(i), Thirteen calendar dates, one date per i = 1-39 record, that apply to all remaining data in the record. Epoch for those data is at 0 hr on the given date. (The purpose of these values is to improve human readability; they are not used by programs that read this file.) Format: YYMMDD TP(i), Time tags and TAI-UTC values and rates for i = 1-39 13 dates. (It is here that leap seconds appear. See Appendix.) Format: TP(i) = TIME, TAI-UTC, UTCDOT where TIME = Time tag for the remaining data, in UTC seconds past 12:00 noon Jan. 1, 2000, or UTC seconds past 0 hours Jan. 1, 1950 (+SSSSSSSSSSS.). Programs that read this file use TIME as epoch for all the remaining data in the record. TIME must be a multiple of 100 seconds. TAI-UTC = TAI-UTC at TIME (+SS.SSSSSS). UTCDOT = Rate of change of TAI-UTC at TIME, in seconds/second (nnnnn.nnnnE-10). Zero by definition since 1 Jan 1972; at that epoch the UTC second was defined to have the same length as the TAI second. Records 15-51: IT(i), Calendar date for data in record, as i = 40-150 discussed above. TP(i), Time tags and TAI-UT1 or TAI-UT1R values i = 40-150 and rates for 37 dates. Format: TP(i) = TIME, UT1, UT1DOT where TIME = Seconds past 2000 or 1950 (see above.) TAI-UT1 = TAI-UT1 at TIME (+SS.SSSSSS). UT1DOT = Rate of change of (TAI-UT1) at TIME, in seconds/second (nnnnn.nnnnE-10). Records 52-88: TP(i), Time tags and polar motion data for 37 i = 151-335 dates, usually the same dates as for UT1. Format: TP(i) = TIME, X, XDOT, Y, YDOT where TIME = Seconds past 2000 or 1950 (see above.) X = X coordinate of polar motion at TIME in arc seconds (+.XXXXX). XDOT = Rate of change of X at TIME in arc seconds/TAI second (+.RRRRR-EE). Y = Y coordinate of polar motion at TIME in arc seconds (+.YYYYY). YDOT = Rate of change of Y at TIME in arc seconds/TAI second (+.RRRRR-EE). Examples of these data may be found in Figures TRK-2-21-1 and TRK-2-21-2. Figure TRK-2-21-1. Format of UTPM STOIC data file with "seconds past 2000" time tags TIMPOL='STOIC/KEOF.LD950322/PT950602 . PREDICTS->950602. UT1TYP=UT1R.', IT( 1)=930910,TP( 1)= -199108800., 28.000000, 0.0000E-10, IT( 4)=940701,TP( 4)= -173707200., 29.000000, 0.0000E-10, IT( 7)=100101,TP( 7)= 315576000., 45.000000, 0.0000E-10, IT( 10)=991231,TP( 10)= 0., 0.000000, 0.0000E-10, IT( 13)=991231,TP( 13)= 0., 0.000000, 0.0000E-10, IT( 16)=991231,TP( 16)= 0., 0.000000, 0.0000E-10, IT( 19)=991231,TP( 19)= 0., 0.000000, 0.0000E-10, IT( 22)=991231,TP( 22)= 0., 0.000000, 0.0000E-10, IT( 25)=991231,TP( 25)= 0., 0.000000, 0.0000E-10, IT( 28)=991231,TP( 28)= 0., 0.000000, 0.0000E-10, IT( 31)=991231,TP( 31)= 0., 0.000000, 0.0000E-10, IT( 34)=991231,TP( 34)= 0., 0.000000, 0.0000E-10, IT( 37)=991231,TP( 37)= 0., 0.000000, 0.0000E-10, IT( 40)=930910,TP( 40)= -199108800., 27.527470, 240.7390E-10, IT( 43)=930928,TP( 43)= -197553600., 27.567560, 271.4260E-10, IT( 46)=931016,TP( 46)= -195998400., 27.612490, 311.1530E-10, IT( 49)=931103,TP( 49)= -194443200., 27.660101, 293.2580E-10, IT( 52)=931121,TP( 52)= -192888000., 27.704720, 273.6060E-10, . . . . . . . . . . . . . . . . . . IT(124)=950127,TP(124)= -155563200., 28.668550, 315.9780E-10, IT(127)=950214,TP(127)= -154008000., 28.715870, 289.0080E-10, IT(130)=950304,TP(130)= -152452800., 28.762859, 339.3200E-10, IT(133)=950322,TP(133)= -150897600., 28.816549, 338.1390E-10, IT(136)=950409,TP(136)= -149342400., 28.868320, 328.4500E-10, IT(139)=950427,TP(139)= -147787200., 28.918819, 319.7110E-10, IT(142)=950515,TP(142)= -146232000., 28.967529, 307.7830E-10, IT(145)=950602,TP(145)= -144676800., 29.014490, 296.2670E-10, IT(148)=100101,TP(148)= 315576000., 45.000000, 317.0000E-10, IT(151)=930910,TP(151)= -199108800.,-.10100,0.12380E-08,0.33040,0.19430E-07, IT(156)=930928,TP(156)= -197553600.,-.09540,0.27750E-08,0.36360,0.23730E-07, IT(161)=931016,TP(161)= -195998400.,-.08280,0.84520E-08,0.39800,0.18670E-07, IT(166)=931103,TP(166)= -194443200.,-.07040,0.19770E-07,0.42230,0.98470E-08, IT(171)=931121,TP(171)= -192888000.,-.04420,0.84590E-08,0.44400,0.11020E-07, . . . . . . . . . . . . . . . . . . IT(291)=950127,TP(291)= -155563200.,-.11650,0.95110E-08,0.47660,0.25570E-07, IT(296)=950214,TP(296)= -154008000.,-.09380,0.16550E-07,0.50860,0.17200E-07, IT(301)=950304,TP(301)= -152452800.,-.04970,0.39790E-07,0.53530,0.15100E-07, IT(306)=950322,TP(306)= -150897600.,-.00290,0.32860E-07,0.54990,0.83750E-08, IT(311)=950409,TP(311)= -149342400.,0.04950,0.34210E-07,0.55630,-.36730E-09, IT(316)=950427,TP(316)= -147787200.,0.10220,0.33200E-07,0.54880,-.92200E-08, IT(321)=950515,TP(321)= -146232000.,0.15150,0.29830E-07,0.52790,-.17490E-07, IT(326)=950602,TP(326)= -144676800.,0.19390,0.24330E-07,0.49500,-.24590E-07, IT(331)=100101,TP(331)= 315576000.,0.00000,0.00000E+00,0.25000,0.00000E+00, Figure TRK-2-21-2. Format of UTPM STOIC data file with "seconds past 1950" time tags. TIMPOL='STOIC/KEOF.LD950322/PT950602 . PREDICTS->950602. UT1TYP=UT1R.', IT( 1)=930910,TP( 1)= 1378771200., 28.000000, 0.0000E-10, IT( 4)=940701,TP( 4)= 1404172800., 29.000000, 0.0000E-10, IT( 7)=100101,TP( 7)= 1893456000., 45.000000, 0.0000E-10, IT( 10)=991231,TP( 10)= 0., 0.000000, 0.0000E-10, IT( 13)=991231,TP( 13)= 0., 0.000000, 0.0000E-10, IT( 16)=991231,TP( 16)= 0., 0.000000, 0.0000E-10, IT( 19)=991231,TP( 19)= 0., 0.000000, 0.0000E-10, IT( 22)=991231,TP( 22)= 0., 0.000000, 0.0000E-10, IT( 25)=991231,TP( 25)= 0., 0.000000, 0.0000E-10, IT( 28)=991231,TP( 28)= 0., 0.000000, 0.0000E-10, IT( 31)=991231,TP( 31)= 0., 0.000000, 0.0000E-10, IT( 34)=991231,TP( 34)= 0., 0.000000, 0.0000E-10, IT( 37)=991231,TP( 37)= 0., 0.000000, 0.0000E-10, IT( 40)=930910,TP( 40)= 1378771200., 27.527470, 240.7390E-10, IT( 43)=930928,TP( 43)= 1380326400., 27.567560, 271.4260E-10, IT( 46)=931016,TP( 46)= 1381881600., 27.612490, 311.1530E-10, IT( 49)=931103,TP( 49)= 1383436800., 27.660101, 293.2580E-10, IT( 52)=931121,TP( 52)= 1384992000., 27.704720, 273.6060E-10, . . . . . . . . . . . . . . . . . . IT(124)=950127,TP(124)= 1422316800., 28.668550, 315.9780E-10, IT(127)=950214,TP(127)= 1423872000., 28.715870, 289.0080E-10, IT(130)=950304,TP(130)= 1425427200., 28.762859, 339.3200E-10, IT(133)=950322,TP(133)= 1426982400., 28.816549, 338.1390E-10, IT(136)=950409,TP(136)= 1428537600., 28.868320, 328.4500E-10, IT(139)=950427,TP(139)= 1430092800., 28.918819, 319.7110E-10, IT(142)=950515,TP(142)= 1431648000., 28.967529, 307.7830E-10, IT(145)=950602,TP(145)= 1433203200., 29.014490, 296.2670E-10, IT(148)=100101,TP(148)= 1893456000., 45.000000, 317.0000E-10, IT(151)=930910,TP(151)= 1378771200.,-.10100,0.12380E-08,0.33040,0.19430E-07, IT(156)=930928,TP(156)= 1380326400.,-.09540,0.27750E-08,0.36360,0.23730E-07, IT(161)=931016,TP(161)= 1381881600.,-.08280,0.84520E-08,0.39800,0.18670E-07, IT(166)=931103,TP(166)= 1383436800.,-.07040,0.19770E-07,0.42230,0.98470E-08, IT(171)=931121,TP(171)= 1384992000.,-.04420,0.84590E-08,0.44400,0.11020E-07, . . . . . . . . . . . . . . . . . . IT(291)=950127,TP(291)= 1422316800.,-.11650,0.95110E-08,0.47660,0.25570E-07, IT(296)=950214,TP(296)= 1423872000.,-.09380,0.16550E-07,0.50860,0.17200E-07, IT(301)=950304,TP(301)= 1425427200.,-.04970,0.39790E-07,0.53530,0.15100E-07, IT(306)=950322,TP(306)= 1426982400.,-.00290,0.32860E-07,0.54990,0.83750E-08, IT(311)=950409,TP(311)= 1428537600.,0.04950,0.34210E-07,0.55630,-.36730E-09, IT(316)=950427,TP(316)= 1430092800.,0.10220,0.33200E-07,0.54880,-.92200E-08, IT(321)=950515,TP(321)= 1431648000.,0.15150,0.29830E-07,0.52790,-.17490E-07, IT(326)=950602,TP(326)= 1433203200.,0.19390,0.24330E-07,0.49500,-.24590E-07, IT(331)=100101,TP(331)= 1893456000.,0.00000,0.00000E+00,0.25000,0.00000E+00, EOP DATA FORMAT EOP data are available as ASCII files in Navigation Portable Namelist format. (Navigation Portable Namelist is a Namelist processor written and maintained by the Navigation Software Development Group.) In addition to the inclusion of nutation parameters, the EOP file differs from the UTPM STOIC file in other important ways: The EOP file may be of any length, whereas the UTPM STOIC file is limited to 13 records for TAI-UTC, 37 records for TAI-UT1, and 37 records for polar- motion X and Y. All EOP data for a single time tag are in a single record, whereas the UTPM STOIC file has three different record types depending on the data type, as noted above. EOP time tags are expressed as Modified Julian Dates; UTPM STOIC time tags are seconds past a particular epoch, such as 12:00 noon, 1 Jan. 2000, or 0 hours, 1 Jan. 1950. All characters in a line following a dollar sign ($) are comments included for convenience but ignored by all programs. Specific inputs are as follows: Records 1-6: Labels and flags Note: Adding blanks to fill out any of these labels or flags to their full width of 6, 25, or 80 characters is unnecessary. EOPLBL character*80 This text label is used in identifying the EOP file; it provides the same information as the TIMPOL record in the UTPM STOIC file. EOPFNG character*80 This text label gives the name of the program used to produce the EOP file, the date and time the file was generated, and the date and time the program was linked. EOPUT1 character*6 This flag indicates whether the data in the file contain TAI-UT1 or TAI-UT1R. The two possible values of this variable are 'UT1' and 'UT1R'. EOPTYP character*6 This flag is used by the ODP to determine whether to use the EOP array or the UTPM STOIC (TP) array for the computation of Earth orientation. The allowed values of this variable are 'EOP' and 'STOIC'. EOPTIM character*25 Date and time (UTC) of creation of the EOP file (dd-mmm-yyyy hh:mm:ss.ffff). EOPTRF character*6 A label denoting the Terrestrial Reference Frame for station locations and site velocities to which the EOP parameters refer; currently the value assigned is 'ITRF93'. EOPCRF character*6 A label denoting the Celestial Reference Frame to which the EOP parameters refer; currently the value assigned is 'ICRF93'. Records 7, 8, ...: EOP data EOP(j,i) double-precision Earth-orientation parameters in 7-element array (7,n) records. There is no restriction on n. EOP(1,i) Modified Julian Date (MJD) for the remaining elements in the record (times are UTC). EOP(2,i) X coordinate of polar motion at time EOP(1,i) in milliseconds of arc (mas). One mas is approximately 3 cm on the Earth's surface. EOP(3,i) Y coordinate of polar motion (mas). EOP(4,i) TAI-UT1 or TAI-UT1R (seconds). EOP(5,i) TAI-UTC (seconds). EOP(6,i) Nutation correction dPsi (mas). EOP(7,i) Nutation correction dEps (mas). EOP records are in strictly increasing time order and may have any record spacing (not necessarily uniform). The file must contain a record at the Modified Julian Date where each leap second occurs within the span of the file. The number of records required depends upon the data span and the desired accuracy. Random variations of UT1 are of the order of 0.07 ms in one day, corresponding to about 3 cm on the surface of the Earth. Systematic sub- daily tidal variations of both UT1 and polar motion exist, also with approximately 3-cm amplitudes. The spacing used in currently delivered EOP files is one day, to allow modeling inertial station locations with approximately 3-cm accuracy. The file format allows records to be more closely spaced if greater accuracy is desired. A sample EOP file is given in Figure TRK-2-21-3. Figure TRK-2-21-3. Sample EOP file. October 1994 records (which are not typographical errors) indicate flexibility of format $ JPL Earth Orientation Parameter File $ Last Data Point 20-MAR-1995 $ Predicts to 24-APR-1995 $ EOPLBL='EOP. LAST DATUM 20-MAR-1995. PREDICTS->24-APR-1995, UT1TYP=UT1. ' EOPFNG='Enter MAKE_EOP 22-MAR-1995 00:37:34 linked 24-OCT-1994 16:22:56' EOPUT1='UT1' EOPTYP='EOP' EOPTIM='22-MAR-1995 00:37:34 ' EOPTRF='ITRF93' EOPCRF='ICRF93' $ $ MJD PM x PM y TAI-UT1 TAI-UTC dPsi dEps $ (mas) (mas) (sec) (sec) (mas) (mas) EOP= 49532.0, 140.00, 213.90, 28.214890, 28.0, -23.54, -7.18, $ 29-JUN-1994 49533.0, 138.50, 212.40, 28.216150, 28.0, -23.95, -7.19, $ 30-JUN-1994 49534.0, 137.00, 211.00, 28.217310, 29.0, -24.12, -7.14, $ 1-JUL-1994 49626.0, -64.50, 198.10, 28.373960, 29.0, -30.49, -6.77, $ 1-OCT-1994 49641.0, -98.20, 222.90, 28.411930, 29., -29.41, -6.08, $ 16-OCT-1994 49642.0, -99.80, 225.30, 28.414420, 29.0, -29.53, -5.93, $ 17-OCT-1994 49656.0, -130.90, 255.40, 28.445640, 29.0, -28.15, -5.76, $ 31-OCT-1994 49663.0, -141.20, 270.80, 28.464470, 29.0, -27.85, -5.31, $ 7-NOV-1994 49670.0, -146.50, 289.10, 28.481500, 29.0, -27.09, -5.02, $ 14-NOV-1994 49677.0, -151.90, 307.90, 28.496910, 29.0, -26.84, -4.99, $ 21-NOV-1994 49684.0, -151.90, 327.70, 28.513890, 29.0, -25.96, -4.25, $ 28-NOV-1994 49691.0, -151.70, 345.40, 28.531520, 29.0, -25.83, -4.27, $ 5-DEC-1994 49701.0, -153.80, 370.90, 28.555710, 29.0, -26.00, -4.04, $ 15-DEC-1994 49716.0, -156.40, 411.20, 28.596170, 29.0, -26.20, -3.72, $ 30-DEC-1994 49718.0, -152.90, 417.10, 28.601450, 29.0, -26.02, -4.09, $ 1-JAN-1995 49720.0, -148.70, 422.90, 28.606980, 29.0, -25.76, -3.66, $ 3-JAN-1995 49722.0, -144.60, 428.20, 28.612890, 29.0, -25.09, -3.72, $ 5-JAN-1995 49724.0, -141.30, 432.50, 28.618810, 29.0, -25.51, -3.72, $ 7-JAN-1995 49749.0, -115.60, 485.40, 28.682430, 29.0, -26.59, -3.85, $ 1-FEB-1995 49750.0, -115.70, 487.10, 28.685320, 29.0, -26.41, -3.91, $ 2-FEB-1995 . . . . . . . . . . . . . . . . . . . . . . . . 49825.0, 75.00, 547.80, 28.892010, 29.0, -26.64, -8.35, $ 18-APR-1995 49826.0, 77.80, 547.10, 28.894710, 29.0, -26.74, -8.57, $ 19-APR-1995 49827.0, 80.50, 546.40, 28.897360, 29.0, -26.71, -8.60, $ 20-APR-1995 49828.0, 83.30, 545.60, 28.900010, 29.0, -26.65, -8.57, $ 21-APR-1995 49829.0, 86.00, 544.80, 28.902720, 29.0, -26.58, -8.51, $ 22-APR-1995 49830.0, 88.70, 544.00, 28.905510, 29.0, -26.50, -8.44, $ 23-APR-1995 49831.0, 91.40, 543.10, 28.908350, 29.0, -26.33, -8.37, $ 24-APR-1995 APPENDIX GLOSSARY Note: For more detailed and rigorous explanations for astronomical terms given below, including specific references, the following two works are recommended: Explanatory Supplement to the Astronomical Almanac, P. Kenneth Seidelman, ed.; University Science Books, Mill Valley, California (1992). IERS Standards (1992), Dennis D. McCarthy, ed.; IERS Technical Note 13, Observatoire de Paris, Paris (July 1992). CEP Celestial Ephemeris Pole: A direction in space, which varies from day to day, about which the Earth appears to rotate on any particular day. The CEP differs from the instantaneous rotation axis of the Earth by periodic terms with amplitudes less than 30 cm. It differs from the pole of the celestial reference frame (ICRF pole; see below) by quantities given by the IAU standard nutation and precessional models (IAU 1980 Theory of Nutation; IAU 1976 Precession) and the offsets (dEps and dPsi; see below) from those models. CIO Conventional International Origin: The point on the Earth's crust representing the mean location of the true pole during the years 1900 - 1905; also called the Mean Pole 1903.0. Formerly used as the terrestrial reference pole. dEps Delta Epsilon: The obliquity component of the offset of the CEP from the direction given by the IAU standard nutation and precessional models, referred to the ICRF (see below). dPsi Delta Psi: The offset in the ecliptic-longitude direction of the CEP from the direction given by the standard nutation and precessional models. IAU International Astronomical Union. ICRF IERS Celestial Reference Frame: A celestial coordinate system, updated yearly by the IERS, based on a set of VLBI-determined coordinates of compact extragalactic radio sources. IERS International Earth Rotation Service: An organization that started operation on 1 January 1988, replacing the earth-rotation section of the Bureau International de l'Heure (BIH) and the International Polar Motion Service (IPMS). IRM IERS Reference Meridian: Reference meridian of the ITRF (see below). IRP IERS Reference Pole: Reference pole of the ITRF (see below). ITRF IERS Terrestrial Reference Frame: A terrestrial coordinate system, updated yearly by the IERS, implicitly defined by a standard set of station-location coordinates. The directions of its axes are continuous with those of the previously used BIH Terrestrial System. KEOF Kalman Earth Orientation Filter: An operational program that produces smoothed and predicted estimates of earth-orientation quantities for the DSN and flight project navigation teams. MJD Modified Julian Date: A shortened version of Julian Date used for convenience. MJD = Julian Date - 2400000.5. Nutation The action of the sun and moon on the Earth's equatorial bulge causes small variations in the direction of the CEP. The short- period (periods less than or equal to 18.6 years) portion of these variations is called nutation; the long-period portion is called precession, and is treated as secular (nonperiodic). ODP Orbit Determination Program. The operational program used by JPL navigation teams to determine spacecraft orbits, planetary gravitational harmonics, and many other parameters. Precession See Nutation (above). STOIC Standby Timing Operations In Contingencies. The program used to generate the UTPM STOIC files. TAI International Atomic Time (French word order): A time scale determined by the International Bureau of Weights and Measures (BIPM; French word order) from analysis of data from, and intercomparison of, many atomic clocks in laboratories around the world. Its unit interval is exactly one SI second at sea level. UTC Coordinated Universal Time: Civil time, formerly called GMT. A time scale running at the same rate (by definition) as TAI, except for the introduction of leap seconds by the IERS as required to keep UTC within 0.9 s of UT1. UT1 Universal Time 1: A measure of the instantaneous rotation angle of the Earth, determined from astronomical and satellite observations corrected for polar motion and measured in time units; also formerly called GMT. It is related to the direction of the IRM in the ICRF, measured around the CEP axis. UT1R UT1 with the effects of short-term tides removed. Short-term tidal effects on UT1 have periods ranging from approximately 5 to 35 days. Long-term tidal effects have periods ranging from approximately 91 days to 18.6 years, and are included in UT1R. The quantities noted as "UT1" in the UTPM STOIC file description or in the EOP file description will always be either all UT1 or all UT1R in a particular file. X,Y Coordinates of the Celestial Ephemeris Pole relative to the IERS Reference Pole. X is measured along the IRM; Y is measured along the meridian 90 degrees W of the IRM.