This is the first ever pic of a human powered ultrasonic rail crack detection jig being used.

There seem to be two ultrasonic probes mounted in tandem near the rails, an oscilloscope like viewing unit, a power pack, a water tank (to wet the rails and provided a 'fluid filled membrane' in which the ultrasonic work the best) and of course an umbrella for the operator :-)
Some background of the ultrasonic crack detection process here. Talegaon, 28th April 2007.