The Dobson Spectrophotometer was developed in 1924 and measures the concentration of ozone in the upper atmosphere. The spectrophotometer compares the absorption spectrum of UV radiation through an ozone rich atmosphere to one that is not. The UV radiation is provided by the sun or moon but the measurements are sensitive to pollution and aerosols and thus are often only used to calibrate measurements from other sources such as satellites. There are many sites around the world equipped with Dobson Spectrophotometers.
Satellite measurements have been made since the Nimbus-7 satellite was launched in 1978. Since then the Total Ozone Mapping Spectrometer (TOMS) has provided daily ozone measurements. Data on other chemical species is measured in order to examine the effects of one on the other.
Taken from: http://www.albany.edu