[Radiance-general] Simulating light ray movement inside swimming pool water. Light sources not in the water

[Lars O. Grobe]

Hi!
>
> Lars, my concern in the dissertation is the glare effect created in 
> the swimming pool and do not allow a lifeguard to search the bottom of 
> the pool. According to the theory found till now, I am interesting in 
> the amount of light reflecting from the surface and the amount that is 
> travelling through the water till it hits the bottom and all the way 
> up. The ratio of the intensities will show me how much glare I have in 
> the swimming pool.
>
Wow, this sounds like a not so trivial problem... ;-) I think you need 
first to study on what surface shapes to expect. On a perfectly even 
surface, you could easily look through to the ground, as long as you do 
not hit the total reflection by very low angles. But as the lifeguard 
will usually be interested in the pool when there are occupants, the 
surface will not be a plane any more, but wavy. And now everything 
depends on the shape - having big, smooth waves will allow good view, 
but small wrinkly waves (ok, here I hit the limits of my English 
language skills) would cause a lot of reflections by total reflection, 
and at the same time caustics resulting in uneven illuminances on the 
ground. If you are able to model the water surface geometries which you 
need to consider, it will be possible to make some estimates on 
visibility of anything below the surface. There are two ways afaik, one 
being rtcontrib, the other one pmap. rtcontrib comes with recent 
distributions, but is not really documented. pmap comes with a nice 
documentation, but is currently supported only with radiance 3.7.

By the way, I think there are two effects to consider. One is glare. 
Even more important may be the total-reflection that simply does not 
permit you to look through a water-air interface (aka the water surface) 
under narrow angles, with or without glare. Glare alone might render the 
task of the lifeguard tiring, but non-visibility renders it impossible...

Cheers, Lars.