Measuring the ozone layer. A researcher making notes next to a Dobson photospectrometer. This instrument is used to measure the total ozone content in the air column directly above the observer. It does this by analysing the spectrum of the sunlight received through the atmosphere. Ozone is a good absorber of high-energy ultraviolet light (UV-B). The more UV-B content of light measured, the lower the ozone content. Such instruments were used to discover the 'ozone hole' over the Antarctic, and now monitor global ozone depletion. This instrument was photographed at the US Climate Monitoring and Diagnostic Laboratory on Mauna Loa, Hawaii.