Changes for SOFA Issue: 2021-01-25 (Release 17)

 Summary of Changes

The changes for this major release fall into the following categories:

1. Extra defensive precautions when computing atmospheric refraction at low altitudes.
2. Application of polar motion handling changed to rigorous. These improvements may result in differences which will be less than 1 mu arcsecond (0.000 001 arc seconds).
3. Expanded documentation including a new cookbook for the SOFA Vector Matrix Library.
4. Typographical and other minor corrections.
5. Changes to the test program.

 Changes to the SOFA FORTRAN Library

1. iau_ATIOQ — Include a limit in altitude (about 3 degrees) below which atmospheric refraction is held constant, for defense and to make it consistent with iau_atoiq.
2. iau_ATIOQ, iau_ATOIQ, iau_APCO, iau_APIO — Application of polar motion calculation made rigorous for canonical consistency.
3. The updates in the following routines were documentation corrections/additions:
   • iau_EE00B — IERS Conventions reference updated to (2003)
   • iau_GST00B — IERS Conventions reference updated to (2003)
   • iau_PMAT06 — IAU reference added
   • iau_PNM06A — Variable renamed to follow SOFA nomenclature
   • iau_PNM80 — Date variables now correctly labelled as TT
   • iau_TRXPV —Action corrected to R^T * PV together with additional note
4. The updates in the following routines are documentation improvements and typographical corrections:
   • iau_AF2A
   • iau_BI00
   • iau_C2I00A, iau_C2T00A, iau_C2T00B, iau_C2T06A, iau_C2TPE, iau_C2TXY, iau_CAL2JD
   • iau_EO06A, iau_EORS, iau_EPB2JD, iau_EPJ2JD
   • iau_FAOM03, iau_FW2M
   • iau_GMST00, iau_GMST06, iau_GST00A, iau_GST06, iau_GST06A, iau_GST94
   • iau_JD2CAL, iau_JDCALF
   • iau_NUM00A
   • iau_PMAT00, iau_PNM00A, iau_PNM00B, iau_POM00, iau_PVU, iau_REFCO
   • iau_RV2M, iau_RXPV
   • iau_TCGTT, iau_TF2A
   • iau_UT1UTC
   • iau_XYS00B, iau_XYS06A
   • iau_ZP, iau_ZPV
5. Test program t_sofa_f.f was updated due to items (1) and (2) above.

 Changes to the SOFA ANSI C Library

1. iauAtoiq — Include a limit in altitude (about 3 degrees) below which atmospheric refraction is held constant, for defense and to make it consistent with iauAtioq.
2. iauAtioq, iauAtoiq, iauApco, iauApio — Application of polar motion calculation made rigorous for canonical consistency.
3. The updates in the following functions were documentation corrections:
   • iauEe00b — IERS Conventions reference updated to (2003)
   • iaugst00b — IERS Conventions reference updated to (2003)
   • iauPmat06 — IAU reference added
   • iauPnm06a — Variable renamed to follow SOFA nomenclature
   • iauTrxpv — Action corrected to R^T * PV together with additional note
4. The updates in the following functions are documentation improvements and typographical corrections:
   • iauAtciqn, iauAticqn
   • iauBi00
   • iauC2i00a, iauC2t00a, iauC2t00b, iauC2t06a, iauC2tpe, iauC2txy
   • iauEo06a, iauEors
   • iauFaom03, iauFk45z, iauFk54z, iauFw2m
   • iauGmst00, iauGst00a, iauGst06, iauGst06a, iauGst94
   • iauJd2cal, iauJdcalf
   • iauNum00a
   • iauPmat00, iauPn00a, iauPn00b, iauPn06, iauPnm00a, iauPnm00b, iauPnm80, iauPom00
   • iauRefco, iauRv2m, iauRxpv
   • iauS00, iauSxpv
   • iautcgtt
   • iauUt1utc
   • iauXys00b, iauXys06a
   • iauZp, iauZpv
5. Test program t_sofa_c.c was updated due to items (1) and (2) above.

The SOFA Board thanks all those who have reported the various issues that go to ensuring the libraries and documentation are kept up-to-date and relevant.

SOFA Release 17: This changes file was updated on 2021 January 8.

  Changes for SOFA Issue: 2021-02-24

The change for this minor release (17a) relates to dealing with leap seconds during the period 1960 and 1971.

Between the introduction of UTC at the start of 1960 and the first leap second at the end of 1971 there were a series of small offsets and rate changes with respect to TAI. The SOFA routine D2DTF takes these into account, but a shortcoming in the algorithm meant that under certain conditions a leap second could be flagged even though none had occurred.

Such cases were extremely rare, and moreover depended to some extent on compiler behaviour, affecting rounding.

SOFA is grateful to the Astropy group for reporting an instance of this bug, which has been corrected.

 Changes to the SOFA FORTRAN Library

• Change to iau_d2dtf. Format for output a 2-part Julian Date (or in the case of UTC a quasi-JD form that includes special provision for leap seconds).

 Changes to the SOFA ANSI C Library

• Change to iauD2dtf. Format for output a 2-part Julian Date (or in the case of UTC a quasi-JD form that includes special provision for leap seconds).

SOFA Release 17a: This changes file was updated on 2021 February 23.