​What is this large yellow, hand held, remote control style detector thing being used at an airport?

Currently in Greece on an island and a group of three men have been walking around the airport clearly taking some sort of measurement.

One of them has this quite large remote control type device, they stop, hold it up in front of them. There is a long pole with a ball on the tip that comes out the top.

The second man behind him periodically holds up his phone, pointing it toward the tip of the ball. They then stop and scribble some sort of measurement (presumably) onto a clipboard.

I’ve Google for large yellow detectors, remote control detectors but no joy. They seem to be clearly measuring something at regular intervals both inside and outside the airport, does anyone know what?

Apologies for the quality of the second photo – the man is outside and there’s a pinhole screen on the window causing some distortion.