The relationship between Chart Datum/LAT and MSS is a vertical offset ‘Z0’. The value Z0 can only be determined by deploying a seabed tide gauge logging @ 15mins over at least two Lunar Cycles (i.e 60 days). Z0 is not constant and varies from place to place. The vertical offset between LAT and MSS is published for specific ports around the world in Admiralty Tide Publications.
To reduce your Bathy Data to Chart Datum or LAT:
- Obtain the Z0 value from the Admiralty Tide book to the nearest tidal port of your survey area.
- Obtain the MSS value from the Tideinfo.txt File
- Compute the LAT/ Chart Datum value using the following calculation:
Raw Depth – MSS Tides - Z0
- Raw depth is 100.00m,
- Tides is low tide @ -0.87m
LAT/Chart Datum = (100.00+0.87-1.50) = 99.37m
Note: This post processing can be carried out using the Tidesinfo.txt file in a spreadsheet application.