One wavelength is affected strongly by ozone, the other is not. The difference between the two is directly related to the total column ozone. Polar orbiting satellites are now used now give a map of total column ozone over the entire globe. To get the vertical profile of ozone through the atmosphere an ozonesonde is generally used. An ozonesonde is an electrochemical cell and radio transmitter attached to a hydrogen filled balloon that can reach a height of about 35km.
Air is drawn through the cell by a small pump.
The solution in the cell reacts with the ozone, producing a small electric current that is directly proportional to the ozone amount. The signal from the cell is converted into a code and transmitted via radio to a receiving station. The Bureau conducts weekly ozonesonde flights from Laverton, near Melbourne. A pilot weekly program, funded by the Cooperative Research Centre for Southern Hemisphere Meteorology, is being conducted at Macquarie Island commencing in December 1996. Dobson spectrophotometers can also be used the derive vertical ozone profiles, the results of which do not have the detail of the ozonesonde.