A new technology that has recently been developed is visual ultrasound.
There are products available now (the image below comes from a Fluke device) that allow you to see a color-coded representation of where the leaks are.
The red center indicates precisely where the leak is, and as you get outside of that leak location, the colors change to green, and then light blue and dark blue, to indicate that we’re moving away from the center of the sound source.
This is a pretty cool factor, but regular ultrasound devices that are not visual still work just fine too.
The way visual ultrasound works is that the testing equipment has an array of sensors, allowing the sensor to sort of triangulate on where the sound is coming from and to graphically represent that.
These devices still take ultrasound measurements – such as Peak, RMS, etc. – but they also allow you to see the location and intensity of the ultrasound.