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 flay 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.

Switzerland uses Superpumas flying 90m over areas to measure radiation on the ground[1] . In around 3 hours they can measure 100 square kilometers.

[1] https://www.tagblatt.ch/ostschweiz/im-tiefflug-ueber-der-sta... (german)