can this be picked up by pir sensor

[pcmad]

question would a scuba diver just surfaced from a dive water temp (10-15c) fully suited up and with hood mask regulator in  a neoprene or trilaminate drysuit bobing on the surface would you be able to pick up the divers heat signature on infrared equipment such as a pir sensor

[DaJMasta]

A PIR sensor isn't really a precision instrument, but maybe some would?  It would be dependent on distance (they're usually not built for large areas like outdoors), and it may depend on its evaluation criteria (how much change is required and whether a drop in temperature would work).

While a diver is going to be warmer, their suits will be designed to hold in heat and their faces will be recently exposed to cold and wet, so it would take some time for the exposed skin to really get above the water temperatures after evaporative cooling and the circulation returning to the surface of the skin.  Then you've only got a small portion exposed in the water, and I would assume the equipment isn't going to be radiating any significant heat.

So the short answer would be maybe, at least in some situations.  If you took a sensitive camera and pointed it at them, you would be able to make something out (at least in calm waters), but with a wider field, a longer distance, and uncertainty in how the thresholds of the sensor are set - you'd need a lot of testing to be reasonably sure.

Maybe someone's done that - I'd assume for locating people for rescue from the air - and written up some details.