Data source:
 
1) Pressure of exerted by water contained in the soil, snow, and canopy 
   from MERRA numerical model, land product "total water store in land 
   reservoirs" (TWLAND) dataset. MERRA is developed at the Global 
   Modelling  Assimilation Office at NASA.

   The model has resolution over longitude 0.6667 deg, over latitude 
   0.5 deg, at has time resolution 1 hours. However, time resolution
   is reduced to three hours for loading computation. Two out of
   three epochs are ignored.

   The land water storage pressure is smoothed and re-gridded to 
   a grid with latitude/longitude resolution of 2048x4096 for loading 
   computation. For a point that land-water mask is greater than zero,
   i.e. not a total water, the pressure is computed by convolving
   the water pressure at the original grid with an exponential
   decay function e^{-d/r} where d is the distance from the new grid 
   point at the original grid point, r is a smoothing parameter chosen to be 
   1/2 of the original grid resolution over latitude.
   
   The dataset at the new grid from 1979.01.01 through 2015.01.01 was 
   fitted to an empirical model that includes the mean pressure and 
   harmonic variations at each grid cell at the following frequencies: 

   SA    1.990968752920D-07  ! Long period  annual
   SSA   3.982127698995D-07  ! Long period  semi-annual
   PI1   7.232384890619D-05  ! Diurnal
   P1    7.252294578148D-05  ! Diurnal
   S1    7.272206167609D-05  ! Diurnal 
   K1    7.292115855138D-05  ! Diurnal
   PSI1  7.312025542667D-05  ! Semi-diurnal
   2T2   1.450459105823D-04  ! Semi-diurnal
   T2    1.452450074576D-04  ! Semi-diurnal
   S2    1.454441043329D-04  ! Semi-diurnal
   R2    1.456432012082D-04  ! Semi-diurnal
   K2    1.458423171028D-04  ! Semi-diurnal
   U3    2.177679627494D-04  ! Ter-diurnal
   T3    2.179670596247D-04  ! Ter-diurnal
   S3    2.181661850283D-04  ! Ter-diurnal
   R3    2.183652533752D-04  ! Ter-diurnal
   K3    2.185643502505D-04  ! Ter-diurnal
   U4    2.904900529562D-04  ! Four-times-a-day
   T4    2.906891498303D-04  ! Four-times-a-day
   S4    2.908882467044D-04  ! Four-times-a-day

   The parameters of the model: The mean, sine, and cosine amplitudes of 
   harmonic variations were computed for the time range of 36 years
   [1979.01.01, 2015.01.01].

   Finally, the contribution of the mean, diurnal, semi-diurnal,
   ter-diurnal, and four-times-a-day surface variations were removed
   from the surface pressure field excreted by land water storage. 
   Annual and semi-annual variations are kept with the data.


2) The land/water mask was derived from the GTOPO30 model. The land-water
   mask has resolution 2048x4096 over latitude and longitude (~9.8 km).
   Lakes bigger than two cells, i.e. 20 km are considered as water. 
   Changes in bottom pressure of these lakes due to changes in their level 
   are not accounted for and their contribution to loading displacements 
   is set to zero. Glaciers with surface bigger than two cells are counted 
   as water. Therefore, changes in the bedrock pressure exerted by 
   glaciers are not accounted for and their contribution to loading 
   displacements is set to zero. The land-water mask at a given cell is 
   a number in a range of 0 to 1 that is equal to the ratio of the area 
   covered by land to the total area of the cell.
 
3) Love numbers were computed by J.-P. Boy. The Love numbers are computed
   in the coordinate system with the center chosen to be the center of mass 
   of the total Earth: solid Earth, land water, ocean, and the atmosphere. 
   Therefore, loading displacements computed with using such Love numbers 
   are the displacements with respect to the center of mass of the total 
   Earth that includes the land water.

   References:

   Petrov L., J.-P. Boy, "Study of the atmospheric
      pressure loading signal in VLBI observations", Journal of
      Geophysical Research, 10.1029/2003JB002500, vol. 109,
      No. B03405, 2004.

   Rienecker, M.M., Suarez M.J., Gelaro R., Todling R., Bacmeister J., 
      Liu E., Bosilovich M. G., Schubert S. D., Takacs L., Kim G.-K., 
      Bloom S., Chen J., Collins D., Conaty A., da Silva A., et al. 
      MERRA ---- NASA's Modern-Era Retrospective Analysis for Research 
      and Applications, J. Climate, 24, 3624--3648, 2011.

  Reichle, R.~H., Koster~R.D, De Lannoy~G.J.M., Forman~B.A., Liu~Q., 
      Mahanama~S.P.P, Tour\'e~A., Assessment and Enhancement of MERRA 
      Land Surface Hydrology Estimates, J. Climate, 24, 6322--6338, 
      2011.
