Interview with Edward Llewellyn: The OSIRIS Mission is
Extended for a Year

The mission of OSIRIS (Optical Spectrograph and InfraRed Imager System), a Canadian instrument that captures data on ozone depletion, has been extended for another year. Since its launch aboard the Swedish satellite Odin two years ago, OSIRIS has proved to be extraordinarily reliable and continues to analyse the Earth's atmosphere.

Edward Llewellyn of the Institute of Space and Atmospheric Studies at the University of Saskatchewan is in charge of the mission. He explained how OSIRIS is different from other missions that are studying the atmospheric environment.

Question - Odin is not the only satellite studying ozone depletion. How does it differentiate from other satellites?

Pr. Llewellyn - The traditional approach to ozone observations is to measure either vertical columns, i.e. the total amount of ozone directly below the satellite, or to use solar occultation to derive a height profile. Thus the generation of a global height profile map takes approximately one month. The Odin approach is to use scattered sunlight to act as a source against which we can measure ozone. As the sunlight travels through the atmosphere so it acquires the signature of the ozone column that it passes through and by making observations of the Earth's atmospheric limb we can recover this ozone height distribution. In this way Odin provides a global height profile map in 1 day. Here Odin/OSIRIS leading the world.

Q - What makes OSIRIS unique?

Pr. Llewellyn - Odin provides global height profile maps of ozone on a daily basis, it can also do the same for aerosols and nitrogen dioxide, an important gas in ozone depletion and in atmospheric pollution.

One area in which OSIRIS has made unprecedented advances is in atmospheric tomography, essentially a CAT scan of the atmosphere. When Odin/OSIRIS was first proposed the idea of tomography was interesting but considered by many to be an academic pipe-dream; indeed our desire to persist was questioned in some places. With OSIRIS we have shown that the atmosphere is structured in ways that we had not been able previously to identify.

The OSIRIS findings and approach are becoming the backbone of most new satellite proposals to study the atmosphere. This means that Canada, and Canadian graduates, will be requested to lead new attempts to improve our understanding of the terrestrial atmosphere. We can also make similar studies on Mars. As dust storms on Mars can last 6 months. It is of value to study them for their potential insight to Earth's duststorms. For a prairie person this is important.

Thus the real potential for OSIRIS and its findings is only limited by our imagination. We are a true research satellite that the capability to provide new and unexpected information that may be of value to Canada.

Q - What recent data did OSIRIS record and what conclusions can be drawn from them?

Pr. Llewellyn - In 2002 the splitting of the Antarctic ozone hole was accompanied by a lessening in the depletion. This persuaded many to suggest that the models, which indicated a recovery of the ozone layer, were correct and that the threat to the atmospheric ozone had been averted by international action. In 2003 the Antarctic ozone hole is larger than ever before and is filling in much slower than normal. Thus if we ignore last year we reach the opposite conclusion. It is perhaps correct to say that we actually don't know and that we need to have as much knowledge as possible. The Earth is a very complicated system and a limited knowledge may be very dangerous.