A new space-borne instrument helps NASA scientists come to a 'comprehensive' conclusion that the earth is being exposed to increasing amounts of solar radiation
the first comprehensive global analysis of National Aeronautics and Space Administration's ( nasa 's) 15-year satellite data reveals that increasing amounts of solar ultraviolet ( uv ) radiation have been hitting the earth's surface, with the thinning of the atmospheric ozone shield (see Down To Earth , Vol 5, No 7).
The nasa analysis is being called comprehensive as it takes the masking effect of clouds and pollution into account. According to atmospheric scientist, Jay R Herman of nasa 's Goddard Space Flight Centre in Greenbelt, Montana, us , the team has used a new and more accurate analytical technique. The technique, which was developed over the past year, is being used to eliminate errors and recaliberate data obtained from the total ozone mapping spectrometer or ( toms ), flown aboard the orbiting Nimbus-7 satellite. toms is a part of nasa 's Mission to Planet Earth, a long-term, coordinated research effort to study the earth as a global system. The new technique involves the use of a space-borne instrument to determine the uv-b radiation at ground level. The Nimbus-7 toms measures neither ozone nor surface uv-b radiation directly. Instead, it measures the amount of radiation scattered back through the ozone layer.
To validate the new technique, the team has compared its findings with those arrived at by ground-based spectrometers in Canada, New Zealand and South America. These earlier ground-based studies on radiation have been comparatively limited as none of them have been in operation long-enough. Moreover, their findings have not been caliberated well-enough. As a result, their findings have been controversial and have reported the decrease and even the lack of any increase in radiation.
According to Herman, "The increase in radiation is the largest in the middle and high latitudes, where the majority live and where most of the agricultural activity takes place." "At 55 N orth -- the latitude at which England, Scandinavia, Germany, Canada and Russia are located -- the average exposure to uv-b radiation has increased by 6.8 per cent, per decade. At 55 S outh -- at which the southern portions of Argentina and Chile are placed -- the increase has amounted to 9.9 per cent, per decade." Herman also found that uv-b radiation increased by two per cent for every one per cent decrease in the ozone layer.
According to the scientists at nasa, the increases need not be a cause for alarm because the amount of uv-b radiation striking the earth's surface could vary routinely by as much as 20 per cent. But they warn that if these trends persist, radiation levels could be high-enough to produce effects like increasing the incidence of skin cancer and cataract in humans, harming crops and affecting marine life. Thanks to international restrictions on key industrial emissions, experts believe that the radiation bombardment is not likely to build towards the dangerous levels as some had once feared.
To ensure that such global ozone data will be available throughout the next decade, nasa plans to continue using both American and international spacecrafts. Another toms spectrometer was launched on July 2, 1996, aboard a nasa Earth Probe satellite called toms/ep . A fifth toms instrument is being prepared for flight in the year 2000, aboard a Russian spacecraft.
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