Role of Satellite Measurements in the Discovery of Stratospheric Ozone Depletion

This chapter discusses the role satellite total ozone measuring instruments have played in the study of stratospheric ozone depletion. By the early 1980s total ozone measured from two NASA satellites had produced a record that spanned more than a decade, with quality comparable with best ground-based stations. It was therefore a puzzle to many why NASA did not report the discovery of the Antarctic ozone depletion until late 1985. This was initially described as a computer error and continues to be described that way in both scientific and popular media. This simplistic labelling has unfortunately served to hide deeper issues about the ability of satellite instruments in making new scientific discoveries as the nature of the satellite retrieval problems make them critically dependent on the availability of prior information. Lack of such prior information and the unavailability of “ground-truth” data were key contributing factors that caused the delay in reporting the discovery of the Antarctic ozone hole, though it was clearly seen in the data by the summer of 1984. The strength of the satellite instruments is their capability to expand the limited view provided by ground-based and aircraft instruments into a global view. This view played a crucial role in making the public and policy makers aware of the seriousness of the ozone depletion problem that led to the phase-out of the ozone-destroying chemicals. This case is even stronger for the surface UV radiation where large spatial and temporal variability due to clouds and aerosols make it very difficult to see patterns in the data without the perspective that only satellites can provide.