Visibility from the air depends on a lot of factors, not just water clarity.
For example:
- wave action (even relatively small random ripples break the light a lot)
- type of bottom (white sand vs. abyssal plain or deep reefs)
- sun location (noon vs early evening/morning)
- cloud cover (can cast shadows)
etc. etc.
So, if the conditions are just right, I believe you'd see a sub at 50-60m, possibly even a bit deeper. 200m is dysphotic zone, where it's basically dark, and you'd not see anything for sure. I'd say in perfect condotions, over a white sand bottom, you'd be able to see about 100m if you know it's there.
But in most of the Pacific, in good weather, calm weather, persicope depth sub would be very visible from the the air.
--smm
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