The drawback to the ultrasonic detector is it can't see like a camera can. The ultrasonic detector may get you to the right pole but after you replace everything on the pole you may still have corona if it was a design problem or maybe it was something benign on a bolt where it wouldn't cause damage for 50 years but keeps the neighbors up at night. The infrared camera can't see a corona problem but the corona camera may see a problem the infrared camera couldn't, if the current flow in a conductor with broken strands is too low to cause heating you would not see a problem with an infrared camera but might see corona from the broken strands. The corona and infrared cameras are complementary technologies. Corona can also occur in enclosed high voltage switchgear, the minimum voltage for corona is about 1,000 volts.
Some people question what corona is unacceptable.
Compare this to a new high quality test equipment specification of 2 to 5 pC partial discharge. Thus if you can image corona with a camera it should be fixed. Many people have seen the images recently of a driver after a crash running for the infield to roll in the grass to smother the invisible flames of an alcohol fire. The DayCor can see the UVc part of the alcohol flame warning the fire crew before they get to the car of the danger to the driver. The DayCor can also see hydrogen flame and rocket plumes.