Low accuracy, long term predict earth PCK
=========================================
Original file name: earth_200101_990628_predict.bpc
Creation date: 2020 April 11 18:17:00 PDT
Created by: Nat Bachman (JPL/NAIF)
Data Sources
Input file: extended EOP created from
JPL EOP file latest.long
(Copied from WWW URL
http://epic.jpl.nasa.gov/nav/eop/latest.long)
Source EOP metadata:
$ JPL Earth Orientation Parameter File
$ Last Data Point 6-APR-2020
$ Predicts to 28-JUN-2020
$
EOPLBL='EOP. LAST DATUM 6-APR-2020. PREDICTS->28-JUN-2020, UT1TYP=UT1. '
EOPFNG='Enter MAKE_EOP 6-Apr-2020 11:04:43 linked 12-Jan-2017 00:15:37 '
EOPUT1='UT1'
EOPTYP='EOP'
EOPTIM=' 6-Apr-2020 11:04:43 '
EOPTRF='ITRF93'
EOPCRF='ICRF93'
Input file: leapseconds kernel naif0012.tls
Coverage
Start time: 2020 JAN 01 00:01:09.183 TDB
Stop time: 2099 JUN 28 00:01:09.182 TDB
UTC Epoch of last datum: 6-APR-2020
Particulars
This is low-accuracy predict PCK file giving the orientation of the Earth as
a function of time for the interval shown above. This PCK file is made from
an extended EOP file which consists of the JPL EOP file named above, with
four extra records appended. These records are designed to add 79 years to
the coverage of the EOP file without affecting interpolated data values for
times within the coverage interval of the original EOP file. Data values
of records in the extended interval are constant, with the exception of
the TAI-UT1 offsets. Those are adjusted so that the corresponding values
of TAI-UT1R are constant.
The terrestrial frame whose orientation is given by this file is ITRF93; the
inertial base frame is Ecliptic of J2000. Rotational effects included are:
-Precession (1976 IAU model)
-Nutation (1980 IAU model)
-Nutation corrections
-Rotation through true sidereal time
-Polar motion
-Nutation corrections
Euler angles have been extracted from the Ecliptic-to-ITRF93 rotation matrix,
and Chebyshev polynomials were fit to the Euler angles. The Chebyshev
expansion degree was 49; the degree of the retained polynomials is 20.
The coverage interval for each set of polynomials is 1 day or less.
This file represents the same earth orientation as does the input EOP file
for the time range:
01-JAN-2020 UTC
28-JUN-2020 UTC
For epochs after the end of EOP coverage, polar motion and nutation
corrections from the EOP file are held constant at values obtained by
extrapolating 1 day from the last source EOP record. TAI-UT1 values are
set so that the corresponding TAI-UT1R values at each epoch of the
extrapolated records are equal. Details of the EOP extrapolation process
are given below.
Let n be the number of data records in the original EOP file. Let
MJD(i) be the epoch of the ith record expressed as a modified
Julian date. The added records have the following
characteristics:
Record n+1: Epoch is MJD(n) + 1. Nutation correction and polar
motion values are obtained by extrapolating to the
epoch a cubic Lagrange interpolating polynomial
fitted to the corresponding data in records n-3 : n.
TAI-UT1 is obtained by converting to TAI-UT1R the
TAI-UT1 data in records n-3 : n, extrapolating an
interpolating polynomial as for the other data, then
converting the extrapolated TAI-UTR1 value to TAI-UT1.
UTC string is consistent with the MJD epoch.
Record n+2: Epoch is MJD(n) + 2. Nutation correction and polar
motion values match those of record n+1. TAI-UT1 is
set so that the corresponding value of TAI-UT1R at
this epoch is that corresponding to TAI-UT1 at the
epoch of record n+1. UTC string is consistent with the
MJD epoch.
Record n+3: Epoch is MJD(n) + 3. Data values are as described for
record n+2, adjusted for this epoch.
Record n+4: Epoch is MJD(n) + 28854. Data values are as described
for record n+2, adjusted for this epoch.
In all of the four records described above, the values of TAI-UT1
have been selected so the corresponding values of TAI-UT1R are
constant and equal to the value resulting from extrapolating the cubic
interpolating polynomial for TAI-UT1R, fitted to the final four values
of TAI-UT1R derived from the original EOP file, to the epoch of
record n+1.
The expected behavior of the interpolation algorithm is as follows:
Time range Interpolation characteristics
============ =============================
Epoch of record 1 to
epoch of record n-1: Interpolation is identical to standard EOP
file.
Orientation error relative to that provided
by a binary PCK derived from the source EOP
file is non-zero due to differences in the
Chebyshev fitting process. Error is at the
1.1 nanoradian level.
Epoch of record n-1 to
epoch of record n: Nearly identical to standard EOP file;
small round-off error will occur.
Orientation error is at the 1.1 nanoradian
level.
Epoch of record n to
epoch of record n+1: Some ringing of interpolated data
will occur. This interval has duration 1 day.
Orientation error relative to that provided
by a binary PCK derived from a JPL EOP
released 4 days after the source JPL EOP file
(thereby providing accurate predicted data
4 days further into the future--up to 2020
July 2) is at the 225 nanoradian level.
Epoch of record n+1 to
epoch of record n+2: Some ringing of interpolated data will occur.
This interval has duration 1 day.
Orientation error measured as for the
interval described above is at the
245 nanoradian level.
Epoch of record n+2 to
epoch of record n+3: Ideally nutation corrections and polar
motion will be constant, as will TAI-UT1R
derived from TAI-UT1 values in the file.
Some round-off error should be expected.
This interval has duration 1 day.
Orientation error measured as for the
interval described above is at the
265 nanoradian level.
Epoch of record n+3 to
epoch of record n+4: Data are as described for records n+2 to
n+3. This interval has duration 79 years.
Orientation difference relative to the
IAU_EARTH reference frame's rotation model
ranges from the 1.25 milliradian level at
the interval start to the 4.75 milliradian
level at the end.