Subject: [IGSMAIL-0662] New ERP Format
From: AC Coordinator
Date: Thu, 7 Jul 1994 11:56:00 PDT

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IGS Electronic Mail      Thu Jul  7 11:56:00 PDT 1994      Message Number 0662
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Author: AC Coordinator
Subject: New ERP Format

Dear colleagues,
 
For your information, included bellow is a description of the the new IGS
standard erp format which is being adopted by all AC starting with the GPS week
756 (July 3/94) reports. This version is a result of discussions amongst all
AC and IERS and hopefully will allow improved EOP resolutions, flexibility and
improved orbit combination.

With many greetings

                   Jan Kouba 

---------------------------------------------------------------------

  Near-term earth orientation format proposal:
  --------------------------------------------

field   contents/HEADER   comment
========================================================================
 mandatory (i.e, all fields 1-10 must be coded should follow the order
	    bellow and separated by at least one blank):
 1      MJD               modified Julian day, with 0.01-day precision
 2      Xpole             10**-5 arcsec, 0.00001-arcsec precision
 3      Ypole             10**-5 arcsec, 0.00001-arcsec precision
 4      UT1-UTC, UT1R-UTC
        UT1-TAI, UT1R-TAI 10**-6 sec, 0.000001-sec precision (usec)
 5      LOD, LODR         10**-6 ms/day  0.001-ms/day precision (us/day)
 6      Xsig              10**-5 arcsec, 0.00001-arcsec precision
 7      Ysig              10**-5 arcsec, 0.00001-arcsec precision
 8      UTsig             10**-6 sec, 0.000001-sec precision (usec)
 9      LODsig            10**-6 sec/day, 0.001-ms/day    "     (us/day)
10      Nr                number of receivers in the solution (integer)
11      Nf                number of receivers with "fixed" coordinates
12      Nt                number of satellites (transmitters) in the solution
                          (integer)
optional (field 11->, only some may be coded, the order is also optional):
13      Xrt               10**-5 arcsec/day 0.01-mas/day precision
14      Yrt               10**-5 arcsec/day 0.01-mas/day precision
15      Xrtsig            10**-5 arcsec/day 0.01-mas/day    "
16      Yrtsig            10**-5 arcsec/day 0.01-mas/day    "
17      XYCorr            X-Y   Correlation 0.01 precision
18      XUTCor            X-UT1 Correlation 0.01    "
19      YUTCor            Y-UT1 Correlation 0.01    "

20 ->   other parameters e.g. DPsi, DEpsi, their sigmas DPsig, DEsig, etc.
	Should be described in the files (what they are, units, etc.)
        
------------------------------------------------------------------------

The .erp file can be form in the following way:
-------------
Before :any optional text/lines. The EOP table starts and is recognized by the
       header, i.e. the character string, "  MJD "
       (the first, optional text line can be used e.g. for software/estimation
       strategy/ITRF version identification/testing)
EOP Table:
 line 1: Column heading starting with "  MJD " (exact headings for f. 1-10)
 line 2: units (in particular for yet undefined fields 20->)
 line 3: values: SEPARATED BY AT LEAST ONE BLANK, leading 0's optional
 line 3:   "        "
   .
   .
 last line: a blank line (optional, only needed if any optional text bellow
	   is coded, otherwise EOF will terminate the values and the file.
 After    : Any (optional) text
-------------

REMARKS:

   -For field numbers 4, 5 UT1-UTC and LOD are recommended. UT1R-UTC, UT1-TAI,
   UT1R-TAI and LODR are acceptable alternatives. The heading should 
   reflect which of these is used. 

   - It is strongly recommended that AC reconstruct the UT1(R)-UTC (UT1(R)-TAI) 
   exactly to correspond to the submitted orbits.Such UT series may be assigned 
   corresponding sigmas, otherwise zero sigmas should be used to indicate fixed
   values or values not to be used in any EOP combination solutions.

   - the rates may be based on solution/apriori EOP. Non zero sigmas will 
   indicate solutions and zero (or omitted) sigmas indicate nominal (apriori) 
   rates.

   - note that by using rates, the EOP discontinuities (e.g. as is the case for
   midnight UT for most AC) can also be modelled without having different EOP
   values at the same (UT midnight).

   - the first 12 fields are widely used now and the  optional part (field
   13-16) should not affect most users, yet it contains  all the necessary
   resolution for precise reconstruction of orbit transformation from
   terrestrial to inertial coordinate frames at the sub-cm level.

EXAMPLE (two line header):
      
(In this example, since the apriori EOP rates are given, no rate sigmas are
 included. Alternatively zero rate sigmas could have been used. The example 
 reconstructs EMR EOP solutions completely, including the EOP discontinuities
 at UT midnights. Note, this is equivalent to giving three EOP values daily,
 i.e. at 0h, 12h and 24h as the given rates are only valid from 0 to 24h
 UT. on each day)
      
  MJD     Xpole   Ypole UT1-UTC  LOD  Xsig Ysig UTsig LODsig Nr Nf Nt  Xrt  Yrt
        10**-5" 10**-5"    usec us/d    10**-5"   us us/d              10**-5/d
49466.50  18315   34988  -80220 2912    18   21   50    0    20 12 25   50 -224 
49467.50  18341   34787  -83260 2746    18   20   60    0    21 12 25   47 -225 
49468.50  18274   34565  -86180 2549    18   21   60    0    20 12 25   44 -225 
49469.50  18284   34280  -88870 2375    18   19   60    0    20 13 24   39 -259 
49470.50  18283   33971  -91410 2266    18   21   60    0    20 13 25   34 -294 
49471.50  18360   33719  -93900 2231    20   22   70    0    20 13 25   32 -277 
49472.50  18414   33480  -96360 2256    16   19   70    0    21 13 25   36 -213 

---End of example------------

[Mailed From: Jan Kouba <[email-masked]>]