Interpolation of SSH

SSH from the OGCM model is provided through a plugin. So far, three plugins are available: One for the AVISO data, with regular time intervals and a Cartesian grid, one for the LLC4320 MITGCM Zarr files available on CNES HAL supercomputer, and one that handles regional HYCOM simulation outputs. One can build their plugin compliant with their SSH inputs using the existing plugin as an example or contact us if they need help. The SSH is interpolated on the SWOT grid and nadir track for each pass and successive cycle if the input data exceeds one cycle. The nadir track has the same resolution as the SWOT grid in the along-track direction, but it is possible to compute it separately with a different along-track resolution. On the SWOT grid, the 2D interpolation is linear in space. No interpolation is performed in time: the SSH on the SWOT grid at a given time corresponds to the SSH of the closest time step. This avoids contamination of the rapid signals (e.g., internal waves) if they are under-sampled in the model outputs. However, note that locally, sharp transitions of the SSH along the swath may occur if the satellite happens to be over the domain at the time of transition between two-time steps. Fig. 3a shows an input SSH as an example. Fig 3b is the interpolated SSH on a 400 km long segment of the SWOT grid crossing the domain.

FIG. 3: SSH (in meters) produced by the MITGCM high resolution model and filtered at 1/12º.

(a): SSH_model simulator output interpolated on the SWOT grid.
(b): Observed SSH, which is the sum of SSH_model and a random realization
of the total SWOT noise with the default parameters of the software.