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IERS Message No. 85                                    February 09, 2006
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               New ocean tide loading routine ready


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


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