SBUV/2 looks down at the Earth’s atmosphere and the reflected sunlight at wavelengths characteristic of ozone. The SBUV/2 wavelength "channels" range from 252 nanometer (nm) to 340 nm. Ozone is measured as a ratio of sunlight incident on the atmosphere to the amount of sunlight scattered back into space. From this information, the total ozone between the instrument and the ground can be calculated.