Summary of Recent, Pending, Proposed, or Suggested IERS Conventions Updates =========================================================================== (last updated 31 July 2007) See also: http://tai.bipm.org/iers/convupdt/convupdt.html Introduction ------------ * add a set of "Guiding Principles" for models to be included in the Conventions -> draft proposal in position paper for Workshop 2007 1. General Definitions and Numerical Standards ----------------------------------------------- * are any updates needed to numerical standards ? * 2006 CODATA value for G = 6.67428 x 10^-11 +/- 0.00067 x 10^-11 * numerical constants to be agreed with IAU Working Group on Numerical Standards of Fundamental Astronomy (chaired by Brian Luzum) 2. Conventional Celestial Reference System and Frame ----------------------------------------------------- * no changes proposed at this time, though new IAU working group formed in 2006 to consider updated frame 3. Conventional Dynamical Realization of the ICRS -------------------------------------------------- * JPL ephemerides updated from DE405 to DE414 (or newer ???) * possible update of planetary masses & constants 4. Conventional Terestrial Reference System and Frame ------------------------------------------------------ 4.1.3 Conventional contributions to local station displacements * clarify meaning of eqn (11) by adopting a set of criteria for conventional contributions -> draft proposal in position paper for Workshop 2007 * requires clarify on the handling of non-tidal loading effects * impose consistency with Chapter 7 models 4.1.5 Realizations of the ITRS * definition of ITRF as realization of ITRS does not seem consistent with systematic differences given in 4.2.4 for permanent tide, timescales, and geocenter motion 4.2.3 Datum specifications for ITRF2000 * possible update of the orientation rate datum to no longer use NNR-NUVEL-1A -> Don Argus has suggested to use a hot-spot model instead -> empirical geodetic models by Corne Kreemer or Hermann Drewes are probably much better and more stable, but differences need to be resolved * possible change of origin definition ??? -> Don Argus suggests not to use center-of-mass (CM) * possible new approaches to handle non-linear station motions, co- and post-seismic motions, other discontinuities, etc 4.2.4 Geocenter motion * define more precisely the concept of geocenter motion; rather than as ITRS -> ITRF effect, perhaps include directly in eqn (1) of Chapter 5 -> draft position paper for Workshop 2007 in preparation * impose consistency with other sections (e.g., Chapter 7), esp in handling of model effects * choice of reference frame for loading effects should be clarified to use CM explicitly in all cases (e.g., Chapter 7 effects) 5. Transformation between the Celestial and Terrestrial Systems ---------------------------------------------------------------- * corrections posted 05 Nov 2004, 18 Oct 2006, 22 Dec 2006, 16 Feb 2007 * new subroutine PMsdnut.for, provided by A. Brzezinski, was posted 19 Sep 2005 for the prograde diurnal luni-solar effect on polar motion (section 5.4.2) * specify that IAU2000A is "official" model recommended for nutation * implementationn of IAU2006 resolutions for precession (Resolution 1) and nomenclature (Resolution 2) under consideration * procedures for handling variations due to unmodeled Free Core Nutation under consideration 6. Geopotential ---------------- * corrections posted 18 Nov 2004, 23 Sep 2005, 22 Mar 2006, 20 Jul 2006 * model for new effect due to oceanic pole tide posted 13 Mar 2006, from Shailen Desai and Jianli Chen (new section 6.3) * should secular and annual changes of the low degree and order geopotential coefficients (besides just C21 and S21) be included, based on long-term SLR analyses ??? * consider accounting for non-tidal geopotential variations -> Frank Lemoine suggests to consider decomposing into solid Earth (mostly static field) and atmospheric components (strong annual components), as with GRACE analyses * update ocean effects to use a consistent ocean tide model throughout all parts of the Conventions -> Richard Biancale to present new model based on FES2004 ocean tide model at Workshop 2007 (section 6.5) 7. Displacement of Reference Points ------------------------------------ 7.1.1 Ocean tidal loading * section completely revised (25 Nov 2006), including provision of routine hardisp.f by Duncan Agnew as a conventional implementation of the ocean tidal loading computation -> Rolf Dach says that hardisp.f uses opposite sign convention from the ocean loading service for the Mf, Mm, and Ssa tides; issue still needs to be resolved * new, improved ocean models added to ocean loading website at http://www.oso.chalmers.se/~loading/ by Hans-Georg Scherneck and Machiel Bos * whole-Earth geocenter motion coefficients also added to ocean loading website for each tide model and text modified to describe proper handling of effect 7.1.2 Solid Earth tides * subroutine dehanttideinel.f updated 20 Jun 2007 to correct: dutc subroutine (from H. Manche) for an error <0.05 mm; step2diu subroutine (from V. Tesmer) for an error that may exceed 0.1 mm -> review continues for some other possible corrections (which effects should be <0.05 mm) 7.1.4 Solid Earth pole tide (01 Sep 2006) * specify IERS conventional mean pole to be linear model given by eqn (23a) & (23b) * correct a typo and account for the anelastic contributions (from J. Wahr) * define theta explicitly as the co-latitude and reconcile with earlier 7.1.5 Oceanic pole tide * model for new effect posted 01 Sep 2006 from Shailen Desai 7.1.? S1/S2 atmospheric pressure tidal loading model * Tonie van Dam and Richard Ray have provided a gridded model for this effect together with implementation software -> loading model under test by SLR & VLBI data analysts; results to be presented at Workshop 2007 -> still need to consider whether to include effects of annual modulation, which leads to sidebands mainly at K1, P1, R2, & T2; could handle these via an admittance approach depending on size of effects [point raised by Richard Ray via Tonie van Dam] -> still need whole-Earth geocenter motion translational model to related CM and crust-fixed frames 7.1.6 Non-tidal atmospheric pressure tidal loading * use of GGFC (and other ?) products needs explanation * users recommended not to apply in routine data reductions for IERS products -> see draft proposal in position paper for Workshop 2007 7.1.? Other non-tidal loading contributions * use of GGFC (and other ?) products needs explanation * users recommended not to apply in routine data reductions for IERS products -> see draft proposal in position paper for Workshop 2007 7.2 Documentation of technique-specific effects * add a set of criteria to determine which technique-specific effects should be mentioned explicitly in IERS Conventions -> consider level of direct impacts on IERS products -> also consider possible indirect effects, e.g., through local co-location site ties * to what level should these effects be documented here versus giving links to external information sources ? * if VLBI antenna thermal deformation model is retained, how should suitable reference temperatures be computed for all VLBI sites (section 7.2.1) ? -> note that local co-location survey ties should be corrected for the temperature-dependent position of VLBI reference point (w.r.t. reference temperature position) 8. Tidal Variations in the Earth's Rotation -------------------------------------------- * corrections posted 15 Nov 2004, 21 Apr 2005, 06 Feb 2006, 28 Apr 2006 * clarification added that zonal tidal corrections should not be applied in exchange of UT1 and LOD values to avoid confusion over exact model values used * recipe for interpolation to arbitrary epochs should be give, following along the lines of the old IERS Gazette #13 (30 Jan 1997) * review of model for diurnal and semidiurnal EOP variations needed -> current model for ocean tidal effects is old and can probably be improvede (e.g., recent work by Dobslaw & Thomas) -> Richard Ray has indicated he might be able to work on this -> new model should perhaps consider effect of S1/S2 atmosphere pressure tides [e.g., de Viron et al., JGR, 110, B11404, 2005]; effect of S1 probably reaches level of 0.2 mas for polar motion and therefore should be included, but current GCM models are not in good agreement with each other -> S2 & S3 tides are probably small enough to ignore for now 9. Tropospheric models ---------------------- * chapter completely revised & updated (28 Jun 2007) by J. Boehm, G. Hulley, A. Niell, E. Pavlis, together with several new subroutines * provide a priori model for hydrostatic gradient due to equatorial bulge -> Johannes Boehm to present results at Workshop 2007 * improvements to GMF mapping function under evaluation -> Johannes Boehm to present results at Workshop 2007 10. General Relativistic Models for Space-time Coordinates and Equations of Motion ------------------------------------------------------------------------ * review nomenclature for coordinate quantities, following the work of IAU Commission 52 on Relativity in Fundamental Astronomy * implement new definition of TDB, following IAU2006 Resolution 3 * perhaps add a new section on clock synchronization, or transformations of proper time to coordinate time, with application to GNSS satellite clocks * specifically, consider adding a description of the conventional models used to model GNSS satellite clocks (e.g., 2*RV/c term) * and consider description of neglected relativistic effects on GNSS clock estimates by reference to published work (e.g., Jan Kouba's GPS Solutions paper, 2004) to inform users of these signatures in published satellite clock results * for user information on the magnitude of terms in eqn (1) for the relativistic corrections to satellite acceleration, the following estimates from Urs Hugentobler might be included: -> the primary effect is the first term (Schwarzschild field), which affects GPS orbits by about 4 mm radially -> the Lense-Thirring precession (frame dragging) in the second term is about two orders of magnitude smaller for GPS, mainly causing a rotation of the orbit nodes by about -4 uas/day -> the DeSitter (geodesic) precession in the third term is about one order of magnitude smaller for GPS, also mainly causing a rotation of the orbit nodes by about 50 uas/day -> neglect of the Earth's oblateness (J2) in eqn (1) introduces an error at the micrometer level for GPS satellites 11. General Relativistic Models for Propagation ----------------------------------------------- * change section 11.2 title from "Laser Ranging" to "Ranging Techniques" and perhaps augment to indicate orders of magnitude of different cases ?. SINEX Documentation ----------------------- * is it worthwhile to document data analysis models in SINEX files ??? -> would require standardized names for all model effects -> ILRS does something like this already for SLR, but not computer parsable ?. Other Items --------------- * analogous to Chapter 9 for tropospheric models, a new chapter or section may be considered for the propagation of radio waves through the ionosphere, including linear combinations of multi-frequency observations, higher-order neglected effects, possible higher-order models, etc * is it necessary to publish a paper Conventions document or is electronic version alone adequate ??? * are standards for conventional software implementations needed ???