I have to admit, I haven't spent any time on a boat as a police officer. In fact, I don't think my agency even owns a police boat. Sure, we have a few reservoirs in the city, but considering they are mostly enjoyed by tourists on two-person paddle boats, the need isn't really there.
I have, however, spent too much time in a rescue boat as a firefighter in Illinois. A river ran through the middle of our county and all water rescue calls were handled as a county-wide mutual aid call. Our two most common calls were for cars driving into the river (there was a major street where if you didn't see the sign to bear left, you drove right down a boat ramp) and people jumping off bridges.
Now, none of these bridges were exceedingly high. I'd guess the furthest fall was 25 feet or so. Nonetheless, we had people that thought this was a good way to commit suicide. And they usually did it at night...in the winter.
TIs for Rescue
During each of these incidents, we could have deployed a thermal imager to help our efforts. First, we could scan the entire area to see if the person was still in the river, head above water. Remember, a TI cannot see through water, so it could not have helped us find people who were actually under the water. However, by scanning the area, we could have seen the unique heat signature of a head or arm poking above the water line.
Second, we could have scanned the shore line. As you know, most suicide attempts are really pleas for help. And when these poor souls land in 40 degree water, they quickly realize not only that jumping in a Northern Illinois river in December was a really bad idea, but they don't really want to die. So, they would frequently self-rescue.
If they self-rescue, they rarely show the courtesy of calling 911 to say, "Hey, I'm not in the water any more...don't bother risking boats and divers in the middle of the night." By scanning the shoreline, we could have seen one of two clues. First, we may have found a heat source where the person was sitting on the shore, gathering his wits. Second, when he pulled himself from the river, he would have left a huge splash of water on the shore. This cold water would chill the shore, creating an unusual cold spot on the shore. As the person walked away, he would leave a diminishing trail of water spots on the ground. This would indicate someone recently left the water and walked away.
Now, neither of these is obviously a guarantee that the same person who jumped is the same person who was on the shore. But, it would have helped us balance the risk we submit rescuers to against the likelihood someone was still in the water.
TIs for Patrol
On open water, there is no practical way to hide the natural heat from a boat or watercraft. Officers doing night time water patrol can use the TI to monitor large areas for suspicious activity. For example, coastal patrols may know of potential smuggling routes. By stationing a patrol boat nearby and monitoring with a thermal imager, officers can track and observe boaters along that path. The key part is that the boaters have no idea they are being watched. Unlike a spotlight, which throws a beam on the target, the TI is passive, merely receiving heat without sending any indication to the target.
If a boat is involved in smuggling, it may be dropping bales in the water. Assisted by a TI, officers can track the bales as well as scan the shore for potential associates who intend to retrieve the bales. Larger boats with significant portions of the hull above the waterline may also demonstrate unique heat signatures that indicate hidden compartments. Again, all of this can be seen without the suspects being aware you are watching.
Obstructions or stranded boaters can also be identified with a TI. Again, as long as the object is above the waterline and has a different temperature than the water, it will give a separate heat signature to the TI. Dark objects can blend into the surface of the water when viewed with a spotlight; however, the heat difference is not hidden, giving officers another tool to help ensure water safety.