An instrument that measures the total ozone in a vertical column of atmosphere. Measurements are made by comparing the amount of backscattered ultraviolet radiation with the amount of incoming solar energy. These changes in this ratio, the earth's albedo, at specific wavelengths can be used to determine the amount of ozone present. Four satellites create global maps daily of the earth's ozone measurements. [Ozone Science and Engineering; v24i6; page399; 2002] [Atmospheric Environment; v34I17; pages 2681-2690; 2000]