From jimr at ngs.noaa.gov Mon Oct 24 08:39:09 2005
From: jimr at ngs.noaa.gov (Jim Ray (NGS 301-713-2850 x112))
Date: Mon, 24 Oct 2005 11:39:09 -0400 (EDT)
Subject: [IGSMAIL-5238]: OTL routine available for testing
Message-ID: <200510241539.LAA05108@ness.ngs.noaa.gov>
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IGS Electronic Mail 24 Oct 08:42:39 PDT 2005 Message Number 5238
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Author: Jim Ray
Dear Analysis Colleagues,
As you might have noticed, the IERS Conventions (2003) are highly ambiguous
on many points concerning implementation of a model for ocean tidal loading
displacments. No routine was provided to compute the displacements and it
is doubtful that any international standard can be said to exist for this
effect currently.
Fortunately, Duncan Agnew (UCSD) has provided a program of his to compute
the ocean tidal loading displacements for a site given the usual amp & phase
values as generated by the Bos-Scherneck website (in BLQ format). Duncan's
implementation considers a total of 119 constituent tides whose amps &
phases are found by spline interpolation of the tidal admittance based on
the 11 main tides. He says this gives a precision of about 0.1% (which is
far better than that of the tidal models, the Earth model information, or
the displacement convolution calculation).
As part of the process to evaluate this routine for possible inclusion in the
future IERS Conventions, it would be very helpful if several groups could
test it against any others regarded as high-accuracy implementations. A
copy of Duncan's code can be obtained at:
ftp://ftp.ngs.noaa.gov/dist/jimr/hardisp.f
Please let me know if you encounter any problems or if you have any
questions. Your feedback is needed to resolve this important issue.
Thanks for your help. And special thanks to Duncan.
--Jim
Run without imputs, the routine hardisp.f returns:
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Usage:
hardisp yr [d-of-yr | month day] hr min sec num samp
Where
the UTC date given is the time of the first term output
num is the number of output epochs to be written out
samp is the sample interval (seconds)
The harmonics file (amp and phase of displacement) is
read from standard input in the BLQ format used by
Scherneck and Bos
Results are written to standard output (units = m):
dU dS dW
using format: 3F13.5
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