================================ EOT08a =================================

EOT08a stands for (E)mpirical (O)cean (T)ide model derived in 2008
by residual analysis of multi-missions (a)ltimeter data. The model 
is available at the anonymous ftp

    ftp.dgfi.badw.de  in directory   pub/EOT08a/data

Detailed information on EOT08a is given in 

Savcenko R., and W. Bosch (2008): EOT08a – empirical ocean tide model
    from multi-mission satellite altimetry. Report No. 81, Deutsches 
    Geodätisches Forschungsinstitut (DGFI), München 

The pdf-version of this report is provided in the directory pub/EOT08a/doc). 

The residual tide analysis was carried out for altimeter data of 
TOPEX, Poseidon, ERS-1, ERS-2, GFO, Jason-1, and ENVISAT, as far as 
acquired between October 1992 and October 2005 (the full live time 
of TOPEX/Poseidon). 

EOT08a consists of M2, S2, N2, K2, 2N2, K1, O1, P1, Q1 and M4 tidal 
constituents. Accordingly, the file pattern in the   ../data   directory is
	xx.eot08a.nc		for ocean tides, and
	xx.load.eot08a.nc	for loading tides
where xx stands for any of the constituents listed above.

Plots for all of  these files may be found under the   ../plots  subdirectory.

The resolution of 7.5’x7.5’ is identical with FES2004 which was used as 
reference model for the residual tide analysis. 

The grids are stored as the COARDS compliant NetCDF files. To save the 
computation time the tidal constants were stored in the complex form. 
The composition of the files may be obtained by the netcdf command    
     ncdump –h  file.nc   
giving in general the following information:

	Dimensions: 
x – number of nodes in the west-east-direction
y – number of nodes in the south-north-direction

Variables:
x (float) 	– longitudes of grid nodes [degree]
y (float) 	– latitudes of grid nodes [degree]
re(float) 	– real part of tidal constants [cm]  (amplitude*cos(phase))
im(float) 	– imaginary part of tidal constants [cm] (amplitude*sin(phase))

The grid files can be also handled by means of the Generic Mapping Tools 
(GMT), version 4.1 or higher. GMT is open source software, developed and 
maintained by Paul Wessel and Walter H.F. Smith (see http://gmt.soest.hawaii.edu/). 
For examples, if filename is replaced by the name of any of the netcdf files 
in pub/EOT08a/data, then

     grd2xyz filename?re 			# will print the real part
     grd2xyz filename?im 			# will print the imaginary part

of the corresponding constituent. Similar

     grdmath filename?im filename?re HYPOT = ampl.grd    # will compute amplitudes
     grd2xyz ampl.grd 					# print amplitudes

     grdmath filename?im filename?re ATAN2 R2D = phases.grd  # will compute amplitudes  
     grd2xyz phas.grd        				# print phases in degree                                                  

The development of EOT08a was funded by the Deutsche Forschungsgemeinschaft (DFG) 
under grant BO1228/5. EOT08a is a public model and it may be freely redistributed 
if appropriate reference is made to the report, mentioned above.

The EOT08a model is distributed in the hope that it will be useful, but DGFI 
provides EOT08a  “as is” without warranty, expressed or implied, as to the use 
or appropriateness of the EOT08a ocean tide model, and there are no warranties 
of merchantability or fitness for a particular purpose or use. 

          Roman Savcenko    and     Wolfgang Bosch

June, 2008