As we discussed in our previous post, ocean visibility can be estimated anywhere on earth using optical sensors from satellites. So, what does this data tell us?
Undersea visibility around the British shores varies a great deal. Notoriously, the South West coast of England has on average better visibility than the South East. Not surprisingly, that's where many of the UK dive destinations are. There are also spots of good visibility around the West and North Coast of Scotland.
Visibility often gets worse closer to the shores and features much higher variations in time. Many factors are at play, including but not limited to disturbed sediments from the shores and river estuaries triggered by tides, waves and currents. The optical analysis in coastal areas is also complicated by interference from the light reflected from land.
So, how accurate these visibility estimates are? Scientists has previously compared ocean colour data from satellites with in situ samples taken by research missions and citizen science projects. The reported correlation is on general high (up to 73% according to some studies), though it highly varies between coastal areas and open sea, as well as across geographic regions.
Divers' visibility reports can help with this task, too. For instance, in the UK Viz Report group divers report visibility to help each other with dive planning. Divers' reports although often subjective, seem to generally align with what can be measured from space. The two data sources often (i.e. in 75% cases) agree on good visibility (>=5m), but satellite estimates are typically much more optimistic when divers report low visibility.
There are of course many caveats to this analysis. The satellite data has limited resolution and visibility readings are averaged across wide geographic areas (4km x 4km regions around dive spots in this analysis). The user reports, in their turn, are notoriously subjective as divers rarely use mathematical rigour in their estimates. Finally, the algorithms currently used for satellite estimates are rather basic and are not calibrated for the divers' needs.
Our team is working on improving the algorithms for undersea visibility estimations by relying on modern artificial intelligence algorithms and by taking user reports into account. If you are a diver and interested in our work, check out our visibility app at https://marla-client.vercel.app (currently in beta testing).
Stay turned for more updates on ocean visibility research!
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