[defrost]

You'd think that was quick, ... but generally this kind of thing would be done from a crop duster airframe flying at an industry standard 70m/sec (252 km/hr).

I'm guessing the local Perth geophysical survey companies that routinely fly magnetics and radiometrics were all fully engaged flying pre booked contract work .. so they dragged in a couple of white transit vans and fitted them out to get the job done.