By DariaBlackwell - 16 Nov 2020
Baltic Sea Hydrographic Commisssion Chart Datum Working Group
I just read an article about an imminent change to Chart Datum (CD) in the Baltic. In tideless seas, the datum referred to is Mean Sea Level, but there are two peculiarities: different countries historically applied different offsets, and in the Gulf of Bothnia the land is rising (and has been since the last Ice Age) by about 1cm a year. To allow for it one had to adjust the depths shown by so much per year x the age of the chart.
To address these issues the countries bordering the Baltic have been working on a new chart datum called BSCD2000 (www.bshc.pro/working-groups/cdwg). With a single Chart Datum, no adjustments will need to be applied when travelling between countries. The land’s rising is well modelled and should be included in future electronic charts. The national hydrographic offices are updating charts to BSCD2000 starting this year through 2024. During this crossover, there is a potentially serious issue with vector charts, such as Navionics, which typically do not state either the age of the source data or the datum and could result in depth errors of up to 0.4m.
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