MAESTRO to Lead Ozone Research

From space, the atmosphere surrounding earth looks remarkably thin and fragile. Yet, without this ethereal envelope of gases to regulate temperature and protect us from the harmful rays of the sun, life on our planet would cease to exist. In the fall of 2002, the Canadian Space Agency will launch SCISAT-1—its first science satellite in nearly three decades—to learn more about how human activity is altering the delicate chemical balance in our stratosphere and troposphere.

One of the main components of the two-year Atmospheric Chemistry Experiment mission will be to measure ozone depletion over the high Arctic using a new instrument developed by Environment Canada's Meteorological Service of Canada (MSC) in partnership with the University of Toronto. The shoebox-sized spectrophotometer—called MAESTRO (Measurements of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation)—is the most advanced in a long line of MSC instruments that have flown on balloons, high-altitude research aircraft and space shuttle missions over the past 10 years.

MAESTRO and other spectrophotometers operate on the principle that different gases absorb different wavelengths of light, ranging from short, ultraviolet (UV) rays to long, near-infrared ones. Each gas, therefore, has its own "fingerprint" or distinct spectrum of absorption. This makes it possible to identify which gases are present from changes in the brightness of sunlight at different wavelengths between light coming directly from the sun and light that has passed through the atmosphere on the way to the spectrophotometer. Ozone, for example, absorbs UV light and is, therefore, essential to preventing high levels of these rays from reaching the earth's surface.

As the sun rises and sets, its rays slice through different layers of the atmosphere and out into space. MAESTRO will be equipped with more than 2000 separate detectors to record the full spectrum of wavelengths emitted by direct sunlight and by sunlight travelling through these layers. These data will then be analyzed to provide precise measurements of gases and aerosol particles at different heights in the atmosphere.

While similar in concept to its predecessors, MAESTRO is the first to have two separate spectrophotometers operating simultaneously to cover the full spectral range. Earlier instruments had to change filters to switch between the UV and visible parts of the spectrum, a process that used up valuable observing time. In order to obtain a complete vertical profile of the atmosphere as the sun is rising and setting, MAESTRO will collect information on the full spectrum corresponding to a given height in just one third of a second. This will allow scientists to detect details in the vertical profile of gases as fine as one kilometre in altitude.

SCISAT-1 will orbit the earth 15 times a day at a height of 650 kilometres, allowing MAESTRO to take measurements of 30 sunrises and sunsets every 24 hours. It will pass over the high Arctic during late winter—the time of year when severe ozone thinning occurs. As the seasons change it will move closer to the equator and pass over the Antarctic, where a major ozone hole develops during the Austral spring in September of each year.

The satellite will be controlled and data collected by the Canadian Space Agency at its ground stations in St. Hubert, Quebec, and Prince Albert, Saskatchewan. Additional data from Environment Canada's ground-based ozone-monitoring network will verify the accuracy of the space observations and add horizontal resolution. MAESTRO's data will be processed at the University of Waterloo and interpreted by MSC and the University of Toronto in near-real time.

Atmospheric scientists with MSC and the University of Toronto will also work closely with York University and Environment Canada's Canadian Meteorological Centre in Montréal to develop the capability to use MAESTRO's observations in models for forecasting chemical constituents—and ozone in particular—in the stratosphere and troposphere.

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