If there’s one thing in scuba diving that’s overly subjective, I’d say it’s visibility. Divers on the same dive, at the same spot may surface and afterwards discuss about the viz, saying different things and referring to it several ways.
It all started as I fill up a new logbook, apparently my second, (geez, I finally filled up the entire logbook#1---yey!!!), I found a portion about “visibility” and I started to wonder how I should fill it up- by feet? By meters? Or should it be as good, bad, okay, excellent—or what?!
So, I looked it up, (yeah, thru google and all…okay!!!), in my attempt to answer my own dilemma. Dictionary defines visibility as the distance at which an object underwater can be eadily identified. Diving instructors say underwater visibility is measured two ways: There is horizontal visibility — how far you can see looking straight ahead — and vertical visibility — how far you can see looking up or down. Hmmm.. sounds easy?? Don’t think so! Again, how do we measure viz? Jacques Cousteau may have had something called a Secchi disk. They say it's a white disk, 4 inches/10 cm in diameter, which is lowered into the water to a depth at which it just disappears from sight. The distance where the disk cannot be seen is recorded, with the length of the line being the visibility. Even more advanced methods with higher precision exist using photometers. Quite an established way to measure, but the problem is that I don’t know anyone in the group who uses a Secchi Disk or where to find it!
So, my next question is: Does measuring visibility accurately really matter?
By understanding the various factors which affect visibility, we can plan our dive excursions to take advantage of better conditions. It’s one way our knowledge of the weather and waves can make each dive a little bit clearer. For photographers, an accurate measurement may be important since their equipment can depend on exact numbers.
For now, as recreational divers, I guess there’s not a very great deal of finding the exact measurement of visibility. Other done bragging (Oh yeah! That dive was an awesome 80 meter viz!”), i think we’re equally safe to just say viz was either terrible or good, okay or excellent.
by: MMO
It all started as I fill up a new logbook, apparently my second, (geez, I finally filled up the entire logbook#1---yey!!!), I found a portion about “visibility” and I started to wonder how I should fill it up- by feet? By meters? Or should it be as good, bad, okay, excellent—or what?!
So, I looked it up, (yeah, thru google and all…okay!!!), in my attempt to answer my own dilemma. Dictionary defines visibility as the distance at which an object underwater can be eadily identified. Diving instructors say underwater visibility is measured two ways: There is horizontal visibility — how far you can see looking straight ahead — and vertical visibility — how far you can see looking up or down. Hmmm.. sounds easy?? Don’t think so! Again, how do we measure viz? Jacques Cousteau may have had something called a Secchi disk. They say it's a white disk, 4 inches/10 cm in diameter, which is lowered into the water to a depth at which it just disappears from sight. The distance where the disk cannot be seen is recorded, with the length of the line being the visibility. Even more advanced methods with higher precision exist using photometers. Quite an established way to measure, but the problem is that I don’t know anyone in the group who uses a Secchi Disk or where to find it!
So, my next question is: Does measuring visibility accurately really matter?
By understanding the various factors which affect visibility, we can plan our dive excursions to take advantage of better conditions. It’s one way our knowledge of the weather and waves can make each dive a little bit clearer. For photographers, an accurate measurement may be important since their equipment can depend on exact numbers.
For now, as recreational divers, I guess there’s not a very great deal of finding the exact measurement of visibility. Other done bragging (Oh yeah! That dive was an awesome 80 meter viz!”), i think we’re equally safe to just say viz was either terrible or good, okay or excellent.
by: MMO
