This is a level 2 gridded data product that has gone under extensive data quality filtering.

Individual elevation measurements are filtered to be for the specific surface type (see above).

When gridding the elevation measurements we first trim off the lowest and highest 20th percentiles before calculating the mean.

The gridded data product has many missing values for land points where the data is inapplicable.

When smoothing the DOT surface we ignore all grid cells in the 1st and 99th precentile and leave these masked similar to a land point. These outlying cells can occur due to satellite altimeter encountering small islands not found in the land mask.

As we apply bias correction to the different satellite modes we have to be careful that the satellite was operating in its standard configuration. For example some months have data points in LRM mode where we usually expect SAR mode. These tracks have to be removed. This was performed manually.