[IGSMAIL-5300]: new ocean tide loading routine ready

[Jim Ray (NGS 301-713-2850 x112)]

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IGS Electronic Mail      07 Feb 05:12:15 PST 2006      Message Number 5300
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Author: Jim Ray

Dear Analysis Colleagues,

A new Fortran routine, written by Duncan Agnew (UCSD), has been posted
which implements in part the recommendations of section 7.1.1 of IERS
Conventions 2003 concerning local site displacements due to ocean tidal
loading (OTL).  The code can be found at the Conventions Update site at
  ftp://tai.bipm.org/iers/convupdt/chapter7/

Given pre-computed site-dependent amp & phase values for the 11 main tides
(in BLQ format), as generated by the Bos-Scherneck OTL service at
  http://www.oso.chalmers.se/~loading/
hardisp.f determines local dU, dS, dW displacements considering a total of
141 constituent tides using a spline interpolation of the tidal admittances.
The precision is about 1%.  Run without inputs, the routine provides usage
information.  Validation test data are included as in-line comments.

Changes have been made in the latest version of hardisp.f so please delete
any earlier versions that you might have.

In test comparisons against a simple OTL routine with no minor tides and no
nodal modulations, Urs Hugentobler (AIUB) found RMS dU differences over
14 days of about 2 mm for a globally distributed network of ~250 stations
using the GOT00.2 ocean model.  Differences tend to be larger at higher
latitudes, with the largest RMS difference being 5.0 mm at OHIG.

Users should also note that Hans-Georg Scherneck has recently added the new
TPXO.7.0 and FES2004 ocean models to his OTL website.  Older models can
be problematic in areas such as Antarctica (King and Padman, GRL, 32, L23608,
2005).

The IERS and the general user communities are deeply indebted to Duncan
Agnew, Machiel Bos, and Hans-Georg Scherneck for their continuing efforts
to support and improve the ocean loading services.  Thanks very much.

--Jim