Can an IR sensor be used to count a swimmers laps?

Hello, I was thinking of building a swim lap counter for my wife. It would set up on a pool lane and the sensor would see her motion as she gets near and spin/kicks off the wall and count a lap an a display. Before starting the project I was wondering if the usual IR sensors seen in the tutorials would work for this application, or would about 3 to 4 feet be too far or if the IR sensor senses a wide degree would the swimmers in neighboring lanes cause be picked up too,etc.?

Thank you!
Bob

I think that would depend entirely on the sensor you choose and on the difference in temperature between the water and your wife.

Paul

Lets be clear as to which type of IR sensor we are talking about? far IR heat detector or near IR beam-break?

Could she just strike a board , connected to a switch as she goes past .

Beware of electricity and swimming pools, use a low voltage battery , check the regulations

hammy:
Could she just strike a board , connected to a switch as she goes past .

Not with a tumble turn no.

And if she's a serious athlete in training, they won't want her to do anything outside the norm, where perfecting the turn is a big thing.

Competitive pools have a board that the athlete kicks off against after a turn and that records the lap; not sure how they make sure the finish time is caught though.

Does IR time-of-flight distance sensing work in water? Swimming pool water is clear enough.

wvmarle:
Does IR time-of-flight distance sensing work in water? Swimming pool water is clear enough.

But water is blue, it absorbs more and more as you go past red to IR.

Check it out: https://www.ijser.org/researchpaper/Comparison-of-Underwater-Laser-Communication-System-with-Underwater-Acoustic-Sensor-Network.pdf

MarkT:
But water is blue, it absorbs more and more as you go past red to IR.

No - pure water is colourless. There are IR absorption bands at a.o. the H-O stretch frequency, other than that as far as I know IR passes through just fine.
In northern regions of the world, and cold places (high up in the mountains) it tends to colour blue due to the blueish algae. In warmer regions the water tends to colour green instead. As people tend to like the blue colour most swimming pools use blue tinted tiles to give it that hue.
I have never heard of underwater IR ranging being used, only ultrasound (sonar) based. That made me wonder, can it be done at all?