This function calculates depth from pressure and adds the channel metadata in the appropriate fields. If the data elements already have a 'depth' channel, it is replaced. Users could specify either 'TEOS-10' or 'seawater' toolbox to use, if it exists. Otherwise, depth is calculated using the Saunders & Fofonoff method.
If there is already a depth channel present, the function replaces the values with the new calculation of depth.
If sea pressure is not present in the RSK structure, it is calculated with the default atmospheric pressure (10.1325 dbar) by
RSKderiveseapressure before deriving salinity when a different value of atmospheric pressure is used.