Subject: [IGSMAIL-67] EARTH ORIENTATION Bul. No 4.
From: IERS
Date: 13 AUG 1992 19:04:58

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IGS Electronic Mail       13-AUG-1992 19:04:58       Message Number 67
***********************************************************************
 
From:     IERS
Subject:  EARTH ORIENTATION Bul. No 4.

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                  *                                         *
                    IGS'92 EARTH ORIENTATION BULLETIN   4
                  *                                         *
                  *******************************************
                                                            12 AUGUST 1992

 1 - EARTH ORIENTATION PARAMETERS (IERS/CB evaluation)       EOP(IERS) 90 C 04

    Date      MJD         x       y       UT1-UTC
    1992                    0.0001"       0.00001s
   (0h UTC)

   JUL   4    48807    -1392.0  3844.0     43823.8
   JUL   5    48808    -1381.0  3863.0     43644.7
   JUL   6    48809    -1368.0  3884.0     43469.1
   JUL   7    48810    -1352.0  3907.0     43307.6
   JUL   8    48811    -1334.0  3933.0     43164.8

   JUL   9    48812    -1316.0  3959.0     43043.1
   JUL  10    48813    -1299.0  3987.0     42937.2
   JUL  11    48814    -1285.0  4016.0     42845.2
   JUL  12    48815    -1276.0  4043.0     42759.4
   JUL  13    48816    -1270.0  4066.0     42676.3

   JUL  14    48817    -1266.0  4084.0     42588.8
   JUL  15    48818    -1259.0  4100.0     42492.2
   JUL  16    48819    -1248.0  4116.0     42383.6
   JUL  17    48820    -1230.0  4134.0     42262.6
   JUL  18    48821    -1206.0  4155.0     42128.5

   JUL  19    48822    -1178.0  4179.0     41983.6
   JUL  20    48823    -1151.0  4203.0     41829.6
   JUL  21    48824    -1125.0  4226.0     41672.5
   JUL  22    48825    -1102.0  4248.0     41516.4
   JUL  23    48826    -1081.0  4270.0     41366.9

   JUL  24    48827    -1062.0  4290.0     41226.3
   JUL  25    48828    -1043.0  4310.0     41096.9
   JUL  26    48829    -1025.0  4328.0     40976.2
   JUL  27    48830    -1006.0  4347.0     40856.0
   JUL  28    48831     -987.0  4365.0     40726.9

   JUL  29    48832     -967.0  4385.0     40579.8
   JUL  30    48833     -947.0  4406.0     40407.7
   JUL  31    48834     -927.0  4430.0     40210.4
   AUG   1    48835     -905.0  4455.0     39996.1
   AUG   2    48836     -883.0  4479.0     39777.2

 2 - INDIVIDUAL SERIES OF EARTH ORIENTATION PARAMETERS
     The series listed hereafter, obtained  by the IGS Processing Centres,
   are described in  the IGS'92 Earth Orientation Bulletin number 2 and in
   the IGSMail Messages.

         2 -a - EOP(CODE) 92 P 02
                Units : 0.0001" for x,y, 0.00001s for UT1.

     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUN  27   48800.50  -1471.2  3700.2                    72.0   1.4  1.5
   JUN  28   48801.50  -1443.3  3730.4  -55335.8          72.0   1.6  1.8   0.9
   JUN  29   48802.50  -1433.7  3764.5  -55459.7          72.0   1.5  1.6   0.9
   JUN  30   48803.50  -1420.1  3787.4  -55582.4          72.0   1.1  1.6   0.9
   JUL   1   48804.50  -1409.0  3818.6   44276.9          72.0   1.0  1.4   0.8

   JUL   2   48805.50  -1405.3  3840.3   44129.3          72.0   1.3  1.7   0.7
   JUL   3   48806.50  -1384.0  3855.4   43960.7          72.0   1.0  1.4   0.7
   JUL   4   48807.50  -1369.8  3874.9                    72.0   1.0  1.0
   JUL   5   48808.50  -1358.4  3901.8   43557.1          72.0   1.0  0.9   0.6
   JUL   6   48809.50  -1348.4  3916.2   43397.9          72.0   0.9  0.8   0.5

   JUL   7   48810.50  -1340.8  3936.3   43261.9          72.0   1.0  0.9   0.6
   JUL   8   48811.50  -1320.0  3965.0   43146.7          72.0   0.8  0.8   0.6
   JUL   9   48812.50  -1307.0  3997.4   43042.6          72.0   0.9  0.9   0.6
   JUL  10   48813.50  -1283.5  4008.1   42957.3          72.0   1.0  1.2   0.6
   JUL  11   48814.50  -1271.9  4035.6                    72.0   1.0  1.0

   JUL  12   48815.50  -1280.3  4060.3   42738.0          72.0   0.9  1.0   0.6
   JUL  13   48816.50  -1266.4  4080.1   42644.4          72.0   1.0  1.1   0.6
   JUL  14   48817.50  -1262.6  4096.8   42539.5          72.0   1.0  1.1   0.6
   JUL  15   48818.50  -1236.1  4109.0   42430.6          72.0   0.9  1.0   0.6
   JUL  16   48819.50  -1225.0  4128.9   42312.8          72.0   1.0  1.1   0.7

   JUL  17   48820.50  -1206.6  4163.2   42181.6          72.0   1.4  1.8   0.7
   JUL  18   48821.50  -1194.0  4176.9                    72.0   1.8  1.7
   JUL  19   48822.50  -1165.1  4189.4   41930.3          72.0   1.3  1.6   0.7
   JUL  20   48823.50  -1133.7  4251.7   41783.6          72.0   1.0  1.4   0.7
   JUL  21   48824.50  -1092.2  4269.5   41637.7          72.0   1.1  1.5   0.6

   JUL  22   48825.50  -1083.8  4277.3   41497.4          72.0   1.0  1.6   0.7
   JUL  23   48826.50  -1073.0  4278.2   41366.4          72.0   1.0  1.2   0.7
   JUL  24   48827.50  -1045.4  4300.7   41237.9          72.0   0.9  1.0   0.6
   JUL  25   48828.50  -1031.5  4327.4   41113.4          72.0   1.0  1.2   0.6

         2 -b - EOP(CSR)  92 P 01
                Units : 0.0001" for x,y, 0.00001s for UT1.
   A recent description of this analysis can be found in IGSMail 62.
     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUL   9   48812.50  -1293.2  4009.5              428          1.5  1.6
   JUL  10   48813.50  -1286.5  4037.5              304          2.4  2.7
   JUL  11   48814.50  -1272.3  4065.8              385          1.4  1.6
   JUL  12   48815.50  -1273.2  4098.0              392          1.5  1.8
   JUL  13   48816.50  -1259.7  4120.3              408          1.6  1.9

   JUL  14   48817.50  -1246.6  4143.8              357          1.7  2.5
   JUL  15   48818.50  -1248.4  4145.7              351          2.0  2.1
   JUL  16   48819.50  -1228.0  4163.4              364          1.8  1.8
   JUL  17   48820.50  -1229.7  4174.8              320          2.2  2.8
   JUL  18   48821.50  -1198.3  4189.4              368          2.3  2.7

   JUL  19   48822.50  -1180.9  4206.4              392          2.1  2.4
   JUL  20   48823.50  -1138.1  4256.9              418          1.5  1.6
   JUL  21   48824.50  -1102.9  4301.6              393          1.7  2.5
   JUL  22   48825.50  -1082.7  4323.7              390          1.8  2.2
   JUL  23   48826.50  -1071.8  4325.6              367          1.9  1.9

   JUL  24   48827.50  -1045.0  4352.9              400          1.7  1.7
   JUL  25   48828.50  -1021.1  4365.1              397          1.5  1.5

         2 -c - EOP(ESOC) 92 P 01
                Units : 0.0001" for x,y, 0.00001s for UT1.
   A recent description of this analysis can be found in IGSMail 62.
     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUN  21   48794.50  -1506.7  3528.1                    24.0   2.6  3.1
   JUN  22   48795.50  -1495.4  3565.3                    24.0   2.2  2.3
   JUN  23   48796.50  -1499.8  3577.9                    24.0   2.3  2.4
   JUN  24   48797.50  -1504.9  3576.1                    24.0   3.2  3.9
   JUN  25   48798.50  -1491.9  3624.7                    24.0   2.8  3.6

   JUN  26   48799.50  -1466.4  3664.1                    24.0   2.6  2.8
   JUN  27   48800.50  -1449.1  3688.7                    24.0   2.6  2.9
   JUN  28   48801.50  -1431.2  3688.4                    24.0   3.1  3.7
   JUN  29   48802.50  -1431.3  3751.5                    24.0   2.7  2.9
   JUN  30   48803.50  -1421.3  3766.5                    24.0   2.8  3.1

   JUL   1   48804.50  -1398.3  3809.6                    24.0   3.7  4.2
   JUL   2   48805.50  -1385.0  3835.6                    24.0   2.6  2.9
   JUL   3   48806.50  -1397.5  3861.8                    24.0   3.7  4.2
   JUL   4   48807.50  -1369.6  3852.9                    24.0   3.7  4.3
   JUL   5   48808.50  -1367.6  3893.1                    24.0   4.3  4.5

   JUL   6   48809.50  -1347.7  3903.2                    24.0   2.9  3.3
   JUL   7   48810.50  -1345.5  3883.8                    24.0   5.6  5.9
   JUL   8   48811.50  -1287.0  3928.2                    24.0   3.3  3.8
   JUL   9   48812.50  -1290.1  3944.3                    24.0   3.9  4.7
   JUL  10   48813.50  -1275.5  3984.6                    24.0   4.4  5.6

   JUL  11   48814.50  -1254.1  4003.6                    24.0   4.4  5.2
   JUL  12   48815.50  -1271.5  4028.8                    24.0   8.1  9.0
   JUL  13   48816.50  -1259.3  4032.2                    24.0   5.0  6.8
   JUL  14   48817.50  -1278.5  4071.6                    24.0   4.1  4.8
   JUL  15   48818.50  -1210.7  4132.3                    24.0   6.3  7.5

   JUL  16   48819.50  -1204.2  4148.7                    24.0   3.9  4.6
   JUL  17   48820.50  -1178.8  4178.0                    24.0   4.9  7.7
   JUL  18   48821.50  -1171.9  4179.0                    24.0   5.9  9.3
   JUL  19   48822.50  -1126.8  4222.5                    24.0   3.8  5.2
   JUL  20   48823.50  -1121.5  4259.0                    24.0   4.3  5.3

   JUL  21   48824.50  -1088.6  4267.0                    24.0   3.5  3.5
   JUL  22   48825.50  -1087.3  4288.9                    24.0   3.5  4.1
   JUL  23   48826.50  -1061.9  4289.8                    24.0   4.7  4.6
   JUL  24   48827.50  -1055.4  4327.2                    24.0   3.7  4.0
   JUL  25   48828.50  -1009.5  4328.6                    24.0   3.5  3.7

   JUL  26   48829.50   -995.8  4347.5                    24.0   4.9  4.9
   JUL  27   48830.50   -987.7  4395.1                    24.0   3.5  3.7
   JUL  28   48831.50   -966.7  4395.9                    24.0   3.9  4.1
   JUL  29   48832.50   -931.4  4383.1                    24.0   4.0  4.6
   JUL  30   48833.50   -945.2  4420.5                    24.0   4.7  5.0

   JUL  31   48834.50   -892.8  4490.5                    24.0   3.8  3.8

         2 -d - EOP(GFZ)  92 P 01
                Units : 0.0001" for x,y, 0.00001s for UT1.
   A recent description of this analysis can be found in IGSMail 60.
     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUN  28   48801.00  -1475.0  3711.0                          10.0 10.0
   JUN  29   48802.00  -1468.0  3738.0                          10.0 10.0
   JUN  30   48803.00  -1442.0  3768.0                          10.0 10.0
   JUL   1   48804.00  -1467.0  3791.0                          10.0 10.0
   JUL   2   48805.00  -1430.0  3813.0                          10.0 10.0

   JUL   3   48806.00  -1415.0  3836.0                          10.0 10.0
   JUL   4   48807.00  -1435.0  3858.0                          10.0 10.0
   JUL   5   48808.00  -1401.0  3866.0                           8.0  9.0
   JUL   6   48809.00  -1405.0  3852.0                           7.0  8.0
   JUL   7   48810.00  -1389.0  3875.0                           7.0  8.0

   JUL   8   48811.00  -1357.0  3908.0                           7.0  7.0
   JUL   9   48812.00  -1321.0  3945.0                           6.0  7.0
   JUL  10   48813.00  -1306.0  3978.0                           8.0  8.0
   JUL  11   48814.00  -1308.0  3992.0                           8.0 10.0
   JUL  12   48815.00  -1300.0  3997.0                           6.0  6.0

   JUL  13   48816.00  -1300.0  4033.0                           6.0  7.0
   JUL  14   48817.00  -1290.0  4054.0                           6.0  6.0
   JUL  15   48818.00  -1277.0  4074.0                           6.0  7.0
   JUL  16   48819.00  -1248.0  4100.0                           7.0  7.0
   JUL  17   48820.00  -1238.0  4119.0                           7.0  8.0

   JUL  18   48821.00  -1209.0  4130.0                           6.0  8.0

         2 -e - EOP(JPL)  92 P 01
                Units : 0.0001" for x,y, 0.00001s for UT1.
   A recent description of this analysis can be found in IGSMail 55.
     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUN  28   48801.50  -1450.6  3757.1                           2.8  3.7
   JUN  29   48802.50  -1428.5  3790.5                           2.6  3.2
   JUN  30   48803.50  -1417.1  3809.0                           2.2  2.6
   JUL   1   48804.50  -1403.0  3837.6                           2.2  2.7
   JUL   2   48805.50  -1393.3  3862.2                           2.3  2.8

   JUL   3   48806.50  -1385.0  3870.2                           2.4  3.1
   JUL   4   48807.50  -1371.5  3897.0                           2.7  3.4
   JUL   5   48808.50  -1356.9  3917.1                           2.6  3.1
   JUL   6   48809.50  -1340.6  3939.9                           2.3  2.8
   JUL   7   48810.50  -1327.1  3946.4                           2.7  3.2

   JUL   8   48811.50  -1306.2  3984.7                           2.3  2.7
   JUL   9   48812.50  -1299.4  3996.6                           2.9  3.6
   JUL  10   48813.50  -1286.8  4026.4                           2.8  3.5
   JUL  11   48814.50  -1270.7  4058.8                           2.1  2.5
   JUL  12   48815.50  -1265.1  4086.5                           2.4  2.9

   JUL  13   48816.50  -1269.2  4105.5                           2.3  2.8
   JUL  14   48817.50  -1258.0  4129.0                           2.5  2.9
   JUL  15   48818.50  -1245.1  4130.1                           2.5  2.9
   JUL  16   48819.50  -1235.8  4153.3                           2.4  2.7
   JUL  17   48820.50  -1213.1  4175.4                           2.5  2.9

   JUL  18   48821.50  -1192.3  4188.0                           3.0  3.5

         2 -f - EOP(JPL)  92 P 02
                Units : 0.0001" for x,y, 0.00001s for UT1.
   A recent description of this analysis can be found in IGSMail 62.
     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUL  17   48820.50  -1208.7  4156.5                           1.3  1.2
   JUL  18   48821.50  -1179.0  4174.0                           1.5  1.2
   JUL  19   48822.50  -1156.7  4202.3                           1.4  1.2
   JUL  20   48823.50  -1126.5  4231.6                           1.0  1.0
   JUL  21   48824.50  -1100.2  4254.3                           1.1  1.3

   JUL  22   48825.50  -1082.2  4273.8                           1.0  1.2
   JUL  23   48826.50  -1064.0  4290.2                           1.1  1.3
   JUL  24   48827.50  -1042.5  4312.4                           1.0  1.1
   JUL  25   48828.50  -1018.5  4333.6                           1.0  1.1

         2 -g - EOP(SIO)  92 P 03
                Units : 0.0001" for x,y, 0.00001s for UT1.
   A recent description of this analysis can be found in IGSMail 64.
     Date                                                        Uncertainties
     1992      MJD        x       y      UT1-UTC  Passes  Span   x    y
UT1-UTC
                                                          hours

   JUL  12   48815.50  -1261.4  4089.8                           1.5  2.0
   JUL  13   48816.50  -1250.4  4110.5                           1.4  1.6
   JUL  14   48817.50  -1252.0  4115.2                           1.7  2.0
   JUL  15   48818.50  -1241.4  4138.3                           1.6  1.7
   JUL  16   48819.50  -1228.5  4155.5                           1.7  1.9

   JUL  17   48820.50  -1200.0  4176.1                           2.0  2.0
   JUL  18   48821.50  -1182.4  4187.8                           2.7  2.8
   JUL  19   48822.50  -1154.2  4214.5                           2.1  2.0
   JUL  20   48823.50  -1130.6  4239.9                           2.4  2.5
   JUL  21   48824.50  -1095.8  4268.2                           1.7  1.9

   JUL  23   48826.50  -1064.6  4313.5                           1.3  1.4
   JUL  24   48827.50  -1044.1  4330.6                           1.4  1.4
   JUL  25   48828.50  -1014.0  4350.4                           1.6  1.7
   JUL  26   48829.50   -998.5  4368.2                           1.6  1.7
   JUL  27   48830.50   -973.7  4391.3                           1.3  1.4

   JUL  28   48831.50   -956.5  4414.2                           1.4  1.5
   JUL  29   48832.50   -940.6  4428.8                           1.6  1.8
   JUL  30   48833.50   -925.4  4453.1                           1.8  1.6
   JUL  31   48834.50   -894.7  4469.8                           1.2  1.3

 3 - COMPARISONS OF GPS, SLR, AND VLBI EARTH ORIENTATION DETERMINATIONS

A paper version of this part, with plots, will be mailed to the IERS Analysis
Centres and to the IGS Processing Centres. Additional copies are available on
request.

 3.1 - GPS: TERRESTRIAL FRAME ORIENTATION STRATEGIES

Various strategies are tested by the GPS Processing Centres for maintaining
the terrestrial frame orientation. The choices concern the nominal orientation
(ITRF90 or ITRF91), the site motion model used to transfer the coordinates at
the reference epoch, the number of fiducial stations that are fixed, and the
source from which the fixed  coordinates are taken. We summarize in Table 3.1
our understanding of these strategies according to the Centres and to the time
periods. Table 3.2 lists the status of the site positions in the various
analyses. It is reminded that the ITRF91 coordinates provided by Altamimi and
Boucher in IGSMail 33 are brought to 1992.5 by means of the combined SLR-VLBI
velocity field associated to ITRF91 (see the 1991 IERS Annual Report, mailed
early August 1992).

 Table 3.1 - HISTORY OF THE TERRESTRIAL FRAME ORIENTATION STRATEGIES.
 -------------------------------------------------------------------------------
     Series             MJD        GPS    Nominal    Fiducials
   (IERS label)     from  to      weeks   refrnce    Nb  source
 -------------------------------------------------------------------------------
 EOP(CODE) 92 P 01  48792-48800  650-650  ITRF90     9   IERS + AM0-2
 EOP(CODE) 92 P 02  48800-48828  651-654  ITRF91     9   IERS       (IGSMail 33)

 EOP(CSR)  92 P 01  48794-48828  650-654  ITRF91     8   IERS       (IGSMail 33)

 EOP(ESOC) 92 P 01  48794-48800  650-650  ITRF91     8   IERS       (IGSMAil 33)
 EOP(ESOC) 92 P 01  48801-48821  651-653  ITRF91     5   IERS       (IGSMail 33)
 EOP(ESOC) 92 P 01  48722-48834  654-655  ITRF91     6   IERS       (IGSMail 33)

 EOP(GFZ)  92 P 01  48794-48821  650-653  ITRF90     9   SIO       (01/91-05/92)

 EOP(JPL)  92 P 01  48794-48821  650-653  ITRF90     3   JPL  (GIG'91+VLBI vel.)
 EOP(JPL)  92 P 02  48820-48828  654-654  ITRF91     8   IERS       (IGSMail 33)

 EOP(SIO)  92 P 03  48780-48834  648-655  ITRF90    26   SIO    (51 IGS'92 days)
--------------------------------------------------------------------------------

Table 3.2 - STATUS OF THE SITE POSITIONS IN THE ANALYSES FOR EOP
-----------------------------------------------------------------------------
                                ........... Processing Centre ...............
                                CODE    CSR     ESOC    GFZ     JPL     SIO
                                ---------------------------------------------
Reference epoch (years-1900):   92.5    92.5    92.5   92.352   92.5    92.57
............................................................................
    Site Name        Name                  Site position status
                                CODE    CSR     ESOC    GFZ     JPL     SIO
----------------------------------------------------------------------------
Albert Head          ALBH                                        e
Algonquin            ALGO        F       F       F       F       F       F
Canberra         CANB/DS40       e       e       e       e       e       F
                     DS41                                                F
                     DS42                                                e
                     DARW                e
Fairbanks            FAIR        e       F       F       F       F       F
Goldstone        GOLD/DS10       F              F/e      e       e       F
                     DS1B                                                F
Graz                 GRAZ
Hartebeesthoek       HART                F               e      e/F      F
Herstmonceux         HERS                       F/e              e
Hobart               HOBA
Kokee Park           KOKB        F       F       e              e/F
                     KOKR                                F               F
Kootwijk             KOSG                e                       e       F
Kourou               KOUR
Madrid            MADR/DS60      F       e       F               F       F
Mas Palomas          MASP        e       e       e                       e
Matera               MATE        F               e               e       F
McMurdo              MCMU        e       e       e       e       e       F
Metsahovi            METS                                        e       F
Mojave               MOJ1
Ny Alesund        NYAL/NALL      e       e       e       F       e       F
Onsala               ONSA                F                       e       F
Pamate               PAMA        e       e       e       e       e       e
Pasadena             MESA
                     JPL1                                                F
                     JPLB                                                F
Penticton            DRAO        e               e               e       e
Pinyon Flat          PINY                F                       e
                     PIN1                                                F
                     PINB                                                F
Richmond             RCMA        e
Saint John's         STJO        e       e
                     SIO1                                                F
                     SIO2                                                F
Santiago             SANT                e       e       e      e/F      e
Taiwan               TAIW        e       e       e       e       e       F
Townsville           TOWN
Tromso               TROM        F                       F      e/F      F
Tsukuba              TSUK
Usuda                USUD        e       e       e       F       e       F
Victoria             PGC1
Wellington           WELL
WestFord             WES1
Wettzell             WETT        F       F               F
                     WTZ1                                                F
Yaragadee            YAR1        F       F       F       F      e/F      F
YellowkniFe          YELL        F       e       F       F       e       F
Zimmerwald           ZIMM
----------------------------------------------------------------------------
           F: fixed           e: estimated        F/e: fixed or estimated
----------------------------------------------------------------------------

 3.2 - VLBI, SLR, GPS EOP DETERMINATIONS: AGREEMENT WITH THE IERS SYSTEM

In this section, the GPS, SLR, and VLBI observations available over the time
period of the IGS'92 Campaign (MJD 48779-48834) are compared to the IERS series
EOP(IERS) 90 C 04, which is a combination of the series of Table 3.3. The
LLR series has only two results during the considered period, so it could not
be included in the comparisons.

  Table 3.3 - IERS OPERATIONAL SERIES OF EOP
  ------------------------------------------------------------------------
  Techn.      Series           Time       Time          EOP determined
                               span      interv.
  ------------------------------------------------------------------------
   VLBI  EOP(NOAA)  92 R 01     24 h     3/4 d     x, y,  UT1, dPsi, dEps
   VLBI  EOP(NOAA)  92 R 02      1 h     1/2 d            UT1
   VLBI  EOP(USNO)  92 R 03     24 h      7  d     x, y,  UT1, dPsi, dEps

   LLR   EOP(UTXMO) 92 M 02      1 h                      UT1

   SLR   EOP(CSR)   91 L 01     72 h      3  d     x, y, "UT1"
   SLR   EOP(DUT)   91 L 02    120 h      5  d     x, y, "UT1"
  ------------------------------------------------------------------------

The GPS series are those listed in Table 3.1. They GPS give the x,y coordinates
of the pole, except CODE, which gives a series of UT1 that is tied at the begin
ning of each week to an a priori value. The "UT1" determinations obtained by
the SLR Analysis Centre at DUT is left free, whereas in the CSR SLR solution,
it is tied to a VLBI solution for periods longer than about 60 days.

The GPS results are obtained from one-day observations of 16 to 18 satellies in
a network of 11 to 29 stations: 14-19 for CODE, 14-20 for CSR,11-18 for ESOC,
22-27 for JPL, and 17-29 for SIO.

Most of the centres treat independently the successive daily arcs, the
exceptions being CODE (three-day overlapping arcs) and GFZ (two-day
overlapping arcs). GFZ estimates the pole coordinates at 0h UT as the mean of
three successive values at Oh UT in the treatment of the two-day arcs. All
other centres estimate the EOP at 12h UT.

Table 3.4 gives the differences of the VLBI, SLR and GPS series with
EOP(IERS) 90 C 04 under the form of a constant bias, corrected for the predicted
value of the systematic difference. In the case of the GPS results, which are
referred directly to ITRF, the predicted bias and its uncertainty are derived
from Table I-3, p.II-13 of the 1991 IERS Annual Report. It reflects the slight
misalignment of the IERS EOP relative to the IERS terrestrial frame. In the
case of the SLR and VLBI results, the expected values are derived from
analyses of previous years results.

Table 3.4 - SYSTEMATIC DIFFERENCES OF EOP RESULTS WITH IERS
--------------------------------------------------------------------------------
Techn       Series           x (0.001")       y(0.001")       UT1(0.0001s)  Nmes
--------------------------------------------------------------------------------
 VLBI  EOP(NOAA) 92 R 01     0.51 +- 0.15     0.36 +- 0.16    -0.20 +- 0.15  12
 VLBI  EOP(NOAA) 92 R 02                                      -0.21 +- 0.15  34

 VLBI  EOP(USNO) 92 R 03     0.04 +- 0.16     0.13 +- 0.21     0.14 +- 0.43   8

 SLR   EOP(CSR)  91 L 01     0.32 +- 0.16     0.43 +- 0.14    -0.29 +- 0.27  20

 SLR   EOP(DUT)  91 L 02     0.17 +- 0.19    -0.37 +- 0.26     6.68 +- 1.46  11

 GPS   EOP(CODE) 92 P 01    -0.78 +- 0.77    -0.77 +- 0.64    16.29 +- 0.52   9
 GPS   EOP(CODE) 92 P 02     0.00 +- 0.37     0.19 +- 0.48     2.45 +- 0.65  29

 GPS   EOP(CSR)  92 P 01    -0.01 +- 0.40     3.12 +- 0.51                   35

 GPS   EOP(ESOC) 92 P 01     0.74 +- 0.39    -1.16 +- 0.57                   41

 GPS   EOP(GFZ)  92 P 01    -2.57 +- 0.44    -2.98 +- 0.56                   27

 GPS   EOP(JPL)  92 P 01     0.14 +- 0.38     1.81 +- 0.50                   28
 GPS   EOP(JPL)  92 P 02     0.42 +- 0.36     0.14 +- 0.45                    9

 GPS   EOP(SIO)  92 P 03     0.63 +- 0.36     1.87 +- 0.45                   54
--------------------------------------------------------------------------------

 3.3 - GPS: HIGH FREQUENCY CORRELATION IN POLAR MOTION

The correlation of high frequency variations in the GPS polar motion results
is estimated in Table 3.5, on the basis of the residuals of each series of
daily values relative to its own smoothing (frequency cutoff: 1 cycle/8 days).
The common periods between two series cover 20 to 38 days.

 Table 3.5 - HIGH FREQUENCY CORRELATION OF DAILY GPS  POLE COORDINATES
                 Left triangle: x                     Right triangle: y
-------------------------------------------------------------------------------
         CSR    ESOC   GFZ    JPL    SIO      CSR    ESOC   GFZ    JPL    SIO
-------------------------------------------------------------------------------
CODE     0.26   0.15   0.41   0.22  -0.15    -0.13   0.03   0.21   0.31  -0.09

CSR       -    -0.09  -0.13   0.05   0.13      -     0.23   0.01   0.19   0.02

ESOC             -     0.46   0.61   0.15             -     0.25   0.22   0.01

GFZ                     -     0.25   0.22                    -     0.31  -0.12

JPL                            -     0.45                           -     0.12
-------------------------------------------------------------------------------

 3.4 - GPS: FORMAL AND ESTIMATED UNCERTAINTIES

Using the  21  days which are common to the six series without change of
reference system (GPS weeks 651-653) we estimate the true uncertainty of the
daily EOP values by the Allan variance (or pair variance) based on the 15 series
of differences two by two (see the 1991 IERS Annual Report, p.II-52). A similar
estimation is performed for the first week of CODE and the last week of JPL,
which cover 9 days each. Table 3.6 shows the uncertainties thus estimated for
every GPS series, together with the  corresponding rms formal uncertainty
provided by the Processing Centre.

 Table 3.6 - ESTIMATED AND FORMAL UNCERTAINTY OF DAILY GPS POLAR MOTION VALUES
    ------------------------------------------------------------------------
    Techn       Series             x (0.001")           y(0.001")      Nmes
                                estim.   formal     estim.   formal
    ------------------------------------------------------------------------
     GPS   EOP(CODE) 92 P 01     0.47     0.18       0.76     0.23        9
     GPS   EOP(CODE) 92 P 02     0.29     0.11       0.37     0.13       21

     GPS   EOP(CSR)  92 P 01     0.68     0.20       0.75     0.22       21

     GPS   EOP(ESOC) 92 P 01     0.87     0.43       1.55     0.52       21

     GPS   EOP(GFZ)  92 P 01     0.97     0.82       0.50     0.86       21

     GPS   EOP(JPL)  92 P 01     0.23     0.25       0.32     0.30       21
     GPS   EOP(JPL)  92 P 02     0.19     0.12       0.45     0.12        9

     GPS   EOP(SIO)  92 P 03     0.50     0.18       0.54     0.20       21
    ------------------------------------------------------------------------

 3.5 - VLBI, SLR, GPS EOP DETERMINATIONS: DAY-TO-DAY AGREEMENT WITH IERS

The series of EOP obtained by VLBI, SLR and GPS already considered in Table
3.4 are considered now under the form of the weighted rms residual to
EOP(IERS) 90 C 04, after the biases of Table 3.4 are taken out. The
statistics are listed in Table 3.7.

 Table 3.7 - WEIGHTED RMS DIFFERENCES OF EOP RESULTS WITH EOP(IERS) 90 C 04
             The biases of Table 3.4 are taken out.
--------------------------------------------------------------------------------
Techn       Series           x (0.001")    y(0.001")    UT1(0.0001s)  Nmes
--------------------------------------------------------------------------------
 VLBI  EOP(NOAA) 92 R 01       0.34         0.47          0.39         12
 VLBI  EOP(NOAA) 92 R 02                                  0.40         34

 VLBI  EOP(USNO) 92 R 03       0.30         0.38          1.17          8

 SLR   EOP(CSR)  91 L 01       0.47         0.55          0.73         20

 SLR   EOP(DUT)  91 L 02       0.63         1.25          7.59         11

 GPS   EOP(CODE) 92 P 01       2.07         1.24          1.37          9
 GPS   EOP(CODE) 92 P 02       0.72         1.03          3.00         29

 GPS   EOP(CSR)  92 P 01       1.18         1.47                       35

 GPS   EOP(ESOC) 92 P 01       1.24         2.35                       41

 GPS   EOP(GFZ)  92 P 01       1.36         1.79                       27

 GPS   EOP(JPL)  92 P 01       0.71         1.28                       28
 GPS   EOP(JPL)  92 P 02       0.28         0.33                        9

 GPS   EOP(SIO)  92 P 03       0.76         0.74                       54
--------------------------------------------------------------------------------