This package of programs is provided to allow computation of the load tides produced on the solid Earth by the ocean tides. The aim is to provide this capability in in a form that will (I hope) be straightforward to use, while at the same time allowing flexibility in combining different tidal and loading models—of which there are now a great many. A particular strength of this package is the ability to combine local and global models without a lot of effort in defining the boundaries between them. The package also includes programs to allow the computed loads to be converted into harmonic constants for any type of tide (including the ocean tide), and to compute the tide in the time domain from these harmomic constants. For completeness a program for direct computation of the solid-Earth body tides is also included.
The development and of this package (past and present) has been (and is) supported by the US National Aeronautics and Space Administration (NASA) through its Solid Earth and Natural Hazards Program (SENH): currently through grant SENH NAG5-13682.
The complete package (a gzipped tar file) is available here; the total size is 30 Mbytes, which will expand to 34 upon uncompressing. However, after the ASCII files have been converted to local binary versions the ASCII can be removed, which will shrink the total size somewhat.
If you are interested in learning more but do not want to download the entire package, here is a PDF of the manual (0.5 Mb).
The programs are written in standard Fortran 77 (I hope). All the files are read with Fortran reads and writes, either binary (for the ocean-model and land-sea files) or ASCII (for the others). One C routine is used to do bitwise AND’s for reading the bitmapped part of the land-sea database. A few UNIX routines are used to provide the local date and to read command-line arguments. The package should compile and execute successfully on any system that supports the GNU Fortran and C compilers. The user interface is via the command line. All data files are exported as ASCII and converted to binary locally, so there should be no issues with byte-ordering. I have successfully run the code on HP-UX, Sun, and Mac OSX.
All the code is freely available (in both the monetary and open-source usages of "free"). Additional discussion is included in the distribution.
If you use this code to produce results that are published, I would appreciate a reference to one of
Agnew, D. C. (1996), SPOTL: Some programs for ocean-tide loading, SIO Ref. Ser. 96-8, 35 pp., Scripps Institution of Oceanography, La Jolla, CA.
Agnew, D. C. (1997). NLOADF: a program for computing ocean-tide loading, J. Geophys. Res.,102, 5109-5110.
and you should also reference any tidal models that you use (references for these are included in the manual).
Note that this list will change with time, as more models are added, and some older models replaced.
Global Models
Schwiderski (1981), which at this point can be said to be included mostly for sentimental reasons.
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CSR 4.0 |
(1999) from the University of Texas Center for Space Research. |
FES 95.2: the third-generation version of the ‘‘Grenoble’’ tide models.
GOT00.2: Version 00.2 (Year 2000) of the Goddard Ocean Tide Model.
TPXO7.0 (2006): Oregon State University TOPEX/Poseidon solution, Version 7.0
Local Models
Gulf of California, from a three-dimensional hydrodynamic model developed by Stock (1976) in a UCSD PhD thesis.
Bay of Fundy, Gulf of St. Lawrence, Strait of Juan de Fuca: local Canadian models based on tide-gauge data. See Lambert et al (1998), J. Geophys. Res. 103, 30231-30244.
San Francisco Bay: interpolation of tide-gauge data.
Bay of Bengal, Bering Sea, Hawaii, Hudson’s Bay, Indian Ocean, Indonesia region, Sea of Japan, Mediterranean, North Atlantic, North Sea, Sea of Ohkotsk, Red Sea, Tasmania region, Yellow Sea: local models, from Oregon State University TOPEX/Poseidon solutions.
August 2009 Verson 3.2.4: fixed bug in hartid to predict the long-period tides correctly.
July 2008 Verson 3.2.3: fixed bug in hartid to remove the permanent tide from the prediction.
March 2007 Verson 3.2.2: Replaced CSR 3.0 by CSR 4.0, and TPXO 6.2 by TPXO 7.0. Added OSU models for Bay of Bengal, Bering Sea, Hudson’s Bay, Indian Ocean, Indonesia region, Sea of Japan, Mediterranean, North Atlantic, North Sea, Sea of Ohkotsk, Red Sea, Tasmania region, and Yellow Sea.
July 2005 Verson 3.2.1: Added one local model (Hawaii OSU model),
June 2005 Verson 3.2: (A) Added two new global models (GOT00.2 and TPXO6.2), (B) revised the local models for Canadian waters using an improved land-sea database, and (C) included an improved Antarctic coastline.
1999 Verson 3.1, added the induced potential to the quantities computed.
June 1996 Version 3.0, the first public distribution, and the first to use the Topex/Poseidon models.
1987 Verson 2, developed for the National Geodetic Survey, combining into a single program specialized for gravity tides.
1981 Verson 1 for internal use only (on a PDP 11-34!), using the Schwiderski models (and some local models).
Here is a list of papers that have referenced the software.
Hans-George Scherneck (Onsala Space Observatory) maintains a Web server that allows you to compute gravity and displacement loads, at one or more sites, from a number of global models.
Another tidal-loading package is GOTIC2 which (like SPOTL) does tilt and strain as well, and includes a detailed coastal and tidal model around Japan. It includes the NAO ocean-tide models, and (optionally) CSR4.0.
The IERS Special Bureau for Loading provides computed displacements for nontidal loads (atmospheric pressure changes, groundwater variations).