Debraw
Contributor
Everything was appropiate. You are right and I am wrong.
Texas specifically....How do you define visibility?
- Thread starter Dee
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OP
archman:
Maybe I should have been more clear but I started this thread in the Swampers forum for a good reason, not an odd one. It's in this club forum because it is addressed to the Texas Swamp Divers and pertains to the constant low viz dive sites we frequent. If members outside the state of Texas want to post, that's great, but we Swampers depend on the viz reports from each other to help us decide if we want to make the trek to a specific dive site....some of which may take us hours to reach. An accurate viz report can save myself, and others, the time and money it takes to get to some of these sites only to find the viz is trashed. I, too, also like to 'know' the person whose making that report so I know they have the experience in the area I'm interested in to be able to give me an accurate report.
I appreciate the links to past posts that covered this subject but I didn't link to them myself because I wanted more answers more specific to our locations.
Its now a good day in the neighborhood!!! 
How funny that a legitimate thread about visibility becomes a thread about,.....well...."threads"!
Define visibility? Let's see...off the top of my head......
I would propose the horizontal visibility of a black target to be the standard for underwater visibility. We show that the appropriate attenuation coefficient can readily be measured with existing simple instrumentation. Diver visibility depends on the photopic beam attenuation coefficient, which is the attenuation of the natural light spectrum convolved with the spectral responsivity of the human eye (photopic response function). In practice, it is more common to measure the beam attenuation coefficient at one or more wavelength bands. We show that the relationship: visibility is equal to 4.8 divided by the photopic beam attenuation coefficient; originally derived by Davies-Colley (1988), is accurate with an average error of less than 10% in a wide variety of coastal and inland waters and for a wide variety of viewing conditions. We also show that the beam attenuation coefficient measured at 532 nm, or attenuation measured by a WET Labs commercial 20 nm FWHM transmissometer with a peak at 528nm are adequate substitutes for the photopic beam attenuation coefficient, with minor adjustments.
Or I suppose it could be the distance that I can still make out an object.
Define visibility? Let's see...off the top of my head......
I would propose the horizontal visibility of a black target to be the standard for underwater visibility. We show that the appropriate attenuation coefficient can readily be measured with existing simple instrumentation. Diver visibility depends on the photopic beam attenuation coefficient, which is the attenuation of the natural light spectrum convolved with the spectral responsivity of the human eye (photopic response function). In practice, it is more common to measure the beam attenuation coefficient at one or more wavelength bands. We show that the relationship: visibility is equal to 4.8 divided by the photopic beam attenuation coefficient; originally derived by Davies-Colley (1988), is accurate with an average error of less than 10% in a wide variety of coastal and inland waters and for a wide variety of viewing conditions. We also show that the beam attenuation coefficient measured at 532 nm, or attenuation measured by a WET Labs commercial 20 nm FWHM transmissometer with a peak at 528nm are adequate substitutes for the photopic beam attenuation coefficient, with minor adjustments.
Or I suppose it could be the distance that I can still make out an object.
Jester
Guest
Huh?
There are a couple variables to be considered. Bren has a lot of trouble driving at night due to her night vision being less than desired. Murk, silt, even cloudy days make for a darker dive. What she might not see at 10' I could be able to spot and define at 15'. I'm a fully in focus vision freak, yet my definition of viz doesn't have the constraints of having the object in good focus, just definable. TEXAS STYLE.
tony (the workin' for the rest of winter texas "diver")
tony (the workin' for the rest of winter texas "diver")
If I'm diving the Guadalupe River, vis gets ranked into three categories.
1. Great (I can see a couple body lengths)
2. Good (I can see one body length)
3. Bad (oh, THERE'S my hand!)
At Spring Lake, I use a similar 3-tiered system... modified SLIGHTLY
1. Great (Caribbean Blue Water; 100+)
2. Hazy (30-50 feet)
3. Poor (<20 feet)
I try to follow freediver's use of the phototopic beam coefficent when possible, assuming the transmissometer I picked up at Dairy Queen has a refreshed set of gerbils to operate the flywheel. However I have the darndest time maintaining a waterproof seal with those ziploc baggies!
Or you smear grease on the bottom of a coffee cup and use it as a makeshift secci disk... I have to use environmentally friendly grease and account for the styrfoam, else the EPA will fine me.
1. Great (I can see a couple body lengths)
2. Good (I can see one body length)
3. Bad (oh, THERE'S my hand!)
At Spring Lake, I use a similar 3-tiered system... modified SLIGHTLY
1. Great (Caribbean Blue Water; 100+)
2. Hazy (30-50 feet)
3. Poor (<20 feet)
I try to follow freediver's use of the phototopic beam coefficent when possible, assuming the transmissometer I picked up at Dairy Queen has a refreshed set of gerbils to operate the flywheel. However I have the darndest time maintaining a waterproof seal with those ziploc baggies!
Or you smear grease on the bottom of a coffee cup and use it as a makeshift secci disk... I have to use environmentally friendly grease and account for the styrfoam, else the EPA will fine me.
In Texas, I define "good' visibility as being able to read my gauge when I put it flat up against my face-plate! Otherwise, it is normally a question of: "Visibility, what's that?" :11:
Cheers!
Cheers!
scubapro50
Contributor
VISIBILITY no problem ....... you're diving the oil rigs out from Gaveston ..... you have a 4 ft. speargun and 3 foot visibility which means anytime you see a fish you have to back up a foot to take your shot
kman458
Guest
i had one of those i picked up and it worked great till i had a massive seal failure at depth, well ok 10 ', and the gerbils all drowned. That was bad but P.E.T.A. was having a "hug a fish dive" right next to where we were and they saw the whole thing. we were lucky to get out with our lives.archman:
ok so i eather use the above or the if i can see my wife then viz is ok:luxhello:, if i can not see her bad viz will be the least of my problems :11:
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