Perhaps others had different practices or flew different instruments such as optical photogrammetry.

If you're seeing gridding at 80m ground clearence perhaps it's crop spraying or perhaps your software is infilling lines from turnpoint position blipping with nothing for the next 50km.

EDIT: I note you submitted this article and have an interest in aerial surveillance programs, I'm simply recounting the practices of one rather busy Australian geophysics company thta was subsumed into Fugro some time past. We considered aircraft and crew safety and had a 20+ year no crash no lives lost record and regularly considered aircraft position signals .. that said we avoided "polluting" the spectrum with broadcasts when aquiring signal and largely relied on off grid checkins (even just three radio blips) ever few completed lines.

I dare say some operators contracted for non EM work (say, radiometric survey) might broadcast during aquisition lines but I find it hard to believe that a good operator would broadcast during EM runs.