WHEN artificial satellites became reality some 40 years ago, meteorologists were among the first to tap into their potential. The main requirement of the weather forecaster was for a snapshot of the atmosphere at a particular place and time, but as spacecraft became more sophisticated, it became obvious that their images could be useful to many other disciplines as well.
They can be used, for example, to monitor ice on rivers, reservoirs and lakes, and allow the probable opening and closing dates of ice prone waterways to be predicted. Another useful application is snow mapping: an accurate assessment of the area covered by snow in a river catchment area can be used to forecast the future supply of water, thereby helping with the management of irrigation systems and with the scheduling of hydro electric power.
Flood waters and drainage patterns can also be monitored by satellites. So too can sedimentation and pollution in our lakes and rivers: most types of pollution are injected at a temperature somewhat different to that of the main body of water and can therefore be detected by pictures taken in the infrared. And water vapour data from a satellite, combined with ground temperatures, can be used to assess the moisture content of the soil, with important implications for productivity in agriculture.
Satellites in low orbits have also been used in California to track the spread of Phylloxera vastatrix - a parasite which attacks and kills the grapevine. It has been found that the temperature of a sick plant differs slightly from that of a normal, healthy one; the difference between healthy and infested zones in a large vineyard can therefore be detected from the infra red images provided by the satellite, long before any signs of infestation are detectable at ground level to the human eye. This allows the damage to be contained.
And at a more adventurous level, drug enforcement agencies throughout the world are excited about the prospects of using environmental satellites to pinpoint illegal crops in remote locations. Poppy fields, which provide the raw material for opium, the cocoa plants from which cocaine is made, and marijuana, all possess a unique "signature" which instruments aboard the satellites can sense. At present these crops are difficult to isolate from all the other flora that appear on satellite images, and the task is made even more difficult by wily growers who, aware they are being watched, intersperse other crops with the illegal drugs. Scientists, however, are hopeful that, with a little practice, all these difficulties will be resolved.