The PC6 is often used in LIDAR work because you need to fly at constant ground speed to get uniform point density which can require an aircraft with low stall speed and highish top speed if the winds are strong. I haven’t looked on FR24 but if he is flying constant groundspeed of 120 knots or so, and relatively low like 3000ft, then probably LIDAR. There are LIDARs that can fly higher and faster, but they are very expensive.
Most orthophoto work in UK is now done at higher altitudes and higher groundspeeds as the cameras are now getting so good. With something like an Eagle Ultracam you can fly 25cm GSD (ie better than Google Earth) at FL180-200 at 250kts+ groundspeed - obviously not PC6 territory.