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Red & Green Lasers on Subs

Morepower

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Mainly just a question. I've noticed on a few Doco's about deep sea exploration that the submersibles now have one red laser and one green laser, when before they just had two red ones. Does anyone know why they use the two different colours ?? I know they use them for determining distance, etc. from an object.
 

Hemlock_Mike

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When scuba diving, I found that after about 40 ' deep, there's very reduced red, yellow and orange for taking pictures. I used a strobe light below 40' even though it was bright to the eye. Without flash, pictures looked blue and green. The water acts as a filter to daylight.
Even the flash was only good for about 15' --- 15' out and 15' back !!

Mike
 

Daedal

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Well... logically speaking, a camera will not care for the difference between wavelengths when it comes to determining distance using a laser scope. There are several ways to check distance using coherent light. Such as:

Beam elevation: say you put the beam at 2 degrees above the horizontal, for every X amount of pixels the dot moved up, that's how far you are.
Multi-beam separation: 2 beams start at 2cm apart and separate at 30mm per meter, the farther apart they are, the farther away they are. This is particularly easier with 2 different wavelengths, and this is what I'm guessing they are using if they are in fact using the laser for distance measurement.
Response time: strobe it and wait for it to come back... used with IR mostly.
Projection size: The bigger/smaller the dot, the farther it is.

All these require very sophisticated computer software and very clear imaging. The easiest being the echo response time, although very difficult in areas saturated with the projected wavelength. On the other hand, if you were to use a green laser where the beam would be pretty much as good as a solid steel rod going through the water to a camera with the aid of a red 'dot' you get very easy measurement and much more accurate results. It took me about 3 months to make a code that uses only 2 red laser pointers to judge distance. I am positive that if I had the ability to have 2 green fully visible beams going through the field of view, it would have been much more accurate and much easier to program ;)

Obviously the 3 months included the full final product... but the logic was a very bad time guzzler! ;D

--DDL
 

Morepower

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Hey DDL, good explanation on the different ways of using lasers to measure distance. It appears they align them slightly outwards so the closer they get to an object the closer the dots come together. The other thing I just thought of, and I hope it is not as stupidly simple as this, but red and green are nautical navigation light colours and I noticed that indeed red was on the port(left) side and green on the starboard.
 

Daedal

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You know... I don't think it would be that simple... It's would be rather odd... Are they trying to tell submarines that they "come in peace"? ;D

If that is the case, then I wouldn't be too surprised if they used sound pulses to measure distance rather than light ::)

--DDL
 

Merlous

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Well I know its rumoured that you can attract different marine life with lasers too so maybe this also has something to do with it, but i really need to look into that more as if thats a case it might be worth getting one for when I am diving.

Hemlock Mike: have you tried using a red filter as well? I find that it helps alot to bring the colours back out, another tip is to take something white down with you and reset the white balance once you get to 12 meters and below. You might already know all that though....
 




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