Loading computation.

   Displacements are computed in frequency domain. The original data are
   re-gridded to the uniform equiangular grid D2699 (10800x5401) with
   refined land-sea mask. The land/water mask was derived from the MOD44W 
   model using the following procedure: a) original MOD4WW mask was 
   re-sampled to resolution 86400x43000 over longitude and latitude;
   b) spherical harmonics transform of degree/order 21,599 was performed; 
   c) the spherical harmonics transform of the mask was multiplied 
   by Blackman window of degree/order 2,699; d) the inverse spherical 
   harmonics transform of degree/order 2,699 was performed over the 
   results to for, the final bandlimited land-sea mask with resolution 
   10800x5401 over longitude and latitude (2'x2'or ~3.7 km). 
   The land-sea mask at a given cell is a number in a range -0.0004 to 
   1.0006 that is equal to the ratio of the area covered by land (i.e. 
   non-ocean in this context) to the total area of the cell.

   Then for every tide, cosine and sine components of ocean tide heights 
   is expanded into spherical harmonic of degree/order 2699. The harmonics
   are scaled by factors that depends on loading Love numbers. These scaled 
   spherical harmonics are used for computing 3D tidal displacement: 
   up, east, and north components. The up component is defined
   as a displacement towards direction orthogonal to the reference ellipsoid.

   Adopted density of sea water: 1025 kg/meter^3.

   The displacement is computed with respect to the center of the total 
   Earth's mass, including the mass of the ocean.

