Detiding

To remove the tidal signal in observations and simulations, two methods are available. If the time sampling is high enough and the time series long enough, the harmonic analysis can be done. Otherwise, the aliasing is too strong and the tidal signal should be estimated from atlases.

To get more information on the tidal wave frequencies, the separability between them and the aliasing impact, look to the showarg command.

Time series

To compute detiding on a tide gauges (single location observation), use the detidor command:

1. Detiding from harmonic analysis

   rep=/ecola/share/tmp/training/GESLA-3.0/
   
   detidor $rep/vigo-vigo-esp-ieo 
           -format GESLA \
           -s 2000/01/01 -f 2020/01/01 \
           -spectrum COASTAL
   

2. Detiding from atlases (TO BE DEBUGGED)

   rep=/ecola/share/tmp/training/GESLA-3.0/
   fes=/ecola/share/tmp/training/FES2014/
   
   detidor $rep/vigo-vigo-esp-ieo 
           -format GESLA \
           -s 2000/01/01 -f 2020/01/01 \
           -tides $fes/WAVE.FES2014.nc \
           -w M2 S2
   

The original, detided and residual time serie is then stored in the file “vigo-vigo-esp-ieo_2000-01-01_2015-12-31.COASTAL_75.00.gnu” as a table with the following columns:

1. Time [days since 1950/01/01]

2. Total sea level [in meters]

3. Detided sea level [in meters]

4. Tidal sea level [in meters]

Altimetry

To compute detiding on along-track altimetry (multiple locations with different time observation), use the altimetry-detidor command:

1. Detiding from harmonic analysis

   rep=/ecola/share/tmp/training/XTRACK-NEA/SLA/
   fes=/ecola/share/tmp/training/
   ln -s $rep/ctoh.sla.ref.TP+J1+J2.NEA.122.nc ctoh.sla.ref.TP+J1+J2.NEA.122.nc
   
   altimetry-detidor ctoh.sla.ref.TP+J1+J2.NEA.122.nc \
                     --tide=no --auto-parse -r 9.9156 \
                     -f NETCDF -gnu=yes -spectrum COASTAL
   

2. Detiding from atlases (TO BE DEBUGGED)

   rep=/ecola/share/tmp/training/XTRACK-NEA/SLA/
   fes=/ecola/share/tmp/training/FES2014/
   ln -s $rep/ctoh.sla.ref.TP+J1+J2.NEA.122.nc ctoh.sla.ref.TP+J1+J2.NEA.122.nc
   
   altimetry-detidor ctoh.sla.ref.TP+J1+J2.NEA.122.nc \
                     --tide=no --auto-parse -r 9.9156 \
                     -o $fes/WAVE.FES2014.nc \
                     -f NETCDF -gnu=yes -spectrum COASTAL
   

The original, detided and residual time serie is then stored in the files “ctoh.sla.TP+J1+J2.debug.*.gnu” (each file beeing a single location time series).

Models

To compute the harmonic analysis on a simulations (multiple location with common time), use the comodo-detidor command:

1. Detiding from harmonic analysis

   rep=/ecola/share/tmp/training/BOBIBE_hourly/
   
   comodo-detidor $rep/2017*.nc \
               -p ssh_w-detiting \
               -s 2017/01/10 -f 2020/01/15 \
               -v ssh_w \
               -d M2 S2
   

2. Detiding from atlases In this mode, comodo-detidor in only looking for an atlas that exctly match its grid, just like the one generated by –only-atlases (as in the harmonic analysis example). Then, to use another atlas, you need to interpolate it on every model grid node (also on vertical levels) and match :

   • the file name convention

     • WAVE-VARNAME-atlas.nc

   • the variable name convention

     • VARNAME_a for ampltitude

     • VARNAME_G for phase lag

   [EXAMPLE COMING SOON]

   rep=/ecola/share/tmp/training/BOBIBE_hourly/
   
   comodo-detidor $rep/2017*.nc \
               --load-atlases \
               -p atlas \
               -s 2017/01/10 -f 2020/01/15 \
               -v ssh_w \
               -d M2 S2
   

The detided variable will be stored in the file “detided-<original file name>” in the directory set with -p option.

To plot it, launch POCViP and follow this tutorial:

rep=/ecola/share/tmp/training/BOBIBE_grid/

pocvip -f $rep/grid.nc