How can scientists tell if the ozone is actually depleted?? They can't just go right up to it and see holes.

the scientist yze the thickness of ozone layer in terms of dobson units .......... they chek the intensity of the UV radiations in incident radiations at a place as compared to the intensity present when 0.01 mm thick ozone layer is present at 0 deg ....... if intensity is increased then it means ozone layer is depleted .............