So I was doing some reading and one article mentioned that a group
mounted an FM transmitter on a hot air balloon. I was also researching
on the methods used by the FCC to measured field strengths. So how does
one go about measuring field strength levels if a company somewhere,
somehow, sometime decides to mount their transmitter on a hot air
balloon to avoid building a tower?

Would the FCC procedures still be valid? I wondering how the field
strength tester would go mobile 30 meters from the radial or
measurement point if the transmitter is changing position constantly.