NASAs Total Ozone Mapping Spectrometer (TOMS) provides measurements that enable scientists to accurately estimate how much of the suns UV-B (290 to 320 nm) radiation reaches the Earth's surface. Too much exposure to these wavelengths causes sunburn in human skin.
The false-color image above is a global map, averaged from TOMS snapshots collected every day over a one-month period, showing where more or less UV radiation reaches the surface. Yellow pixels show the highest levels of radiation at the surface, red and pink hues are intermediate values, and white indicates little or no UV exposure.
The TOMS sensor flies in a polar orbit, crossing the equator every day at 12 noon local time, allowing it to measure the total amount of ozone in a column of atmosphere as well as cloud cover over the entire globe. Ozone and clouds absorb most of the ultraviolet light passing through the atmosphere. TOMS also measures the amount of solar radiation escaping from the top of the atmosphere. It is the combination of those three measurements that enables scientists to accurately estimate the amount of UV radiation that reaches the Earth's surface.
Ultraviolet radiation exposure data and images.
Data courtesy TOMS science team, NASA Goddard Space Flight Center