The Science of ScubaWeather - Visibility

The key feature that sets ScubaWeather apart from other weather forecasts for scuba diving is the scientific calculation of the underwater visibility. I developed an algorithm that combines daily satellite spectral data of the water clarity, the physics of underwater optics, and the biology of how the human eye adapts to different light levels to estimate how far you should be able to clearly see underwater. More specifically, how your eyes can detect contrast, e.g., a shark, from the background. We take it for granted, but it is a richly convoluted subject, touching on physics and biology.

I briefly describe in the About Us page how the origins of ScubaWeather began with a search to estimate underwater visibility. I was working offshore as the Chief Scientist for an environmental sampling program. This project was a little unique in that we were also using a small remotely operated vehicle (ROV) to take pictures of a pipeline on the bottom. On some days you couldn't see anything on the bottom because there was so much organic matter (phytoplankton) and suspended silt in the water that the pictures were full of "marine snow." Then on the following morning it would clear up, only to get worse by the evening. This got me to thinking that if I could forecast the water clarity/visibility a day or two ahead, then I could pick the ideal time to do the ROV ops.

What began as a simple quest, became an extended adventure down the rabbit hole. My initial search uncovered many posts from divers asking if visibility could be provided for a dive site, but no answers. Diving deep (yup, pun intended) into the literature on the subject I found the pioneering work R.W. Priesendorfer began in the 1950’s for the US Navy on underwater visibility.

There may well be those who can find good reason to criticize certain aspects of how I developed the visibility algorithm. To them I quote from Priesendorfer's Hydrologic Optics Volume II.

Nature Seen Through Half-Shut Eyes

"A man who takes a magnifying glass into a picture gallery and examines the canvases at a distance of 3 inches may acquire much interesting information about the texture of paint, but he does not see the picture. It is better to stand away. If trivial details still intrude, it is better to half-shut the eyes. As a final step, it is well to shut the eyes completely and think about what has been seen."
J.L. Synge Science, 5 October 1962

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