THE COMPLETE COSMOS Chapter 11: Earth Patrol Launched into Earth orbit, the satellites that monitor the health of our planet - ozone, melting ice-caps, weather, deforestation, navigation. Outline From Earth-orbit, satellites keep watch for us. Meteosat scans global weather patterns. It tracks severe storms - saving lives and minimizing disruption. And to reduce flooding, satellite images assist engineers select the best locations for dams and barriers. The Topex-Poseidon satellite measures changes in sea level and ocean temperature. Our weather is driven by exchanges between the oceans and the atmosphere. In the Pacific, satellites reveal the phenomenon of El Nino. Thanks to satellites, ships avoid fog banks, icebergs and rough seas. Satellites enable mariners to make accurate navigational fixes. Earth's ever-changing environment is monitored by satellites volcanic eruptions, industrial emissions, the ozone hole, global warming and the damage inflicted by oil spills, fires and the destruction of the rainforest. The SPOT satellite provides a fresh perspective on urban and rural developments – by combining images to produce 3-D pictures. Satellite radar gets beneath clouds of volcanic dust and the sands of the Sahara. Agriculture benefits as false-color satellite images check the health of crops and direct spray planes to where they are needed. Sub-chapters Keeping Watch • Satellites chart the Earth. They help us understand the workings of planet. They speed information around the globe. • The launch of Meteosat - and its vantage point 36,000 kilometers above the equator. • Global weather. How satellites keep track of hurricanes and tornado-generating storms. Storms and Floods • How meteorologists use satellite data to produce weather forecasts that help save lives and minimize disruption. • To reduce the risk of severe flooding, engineers use satellite images to pinpoint the best locations for barriers and dams. Oceans and Atmosphere • From orbit, Topex-Poseidon scans the oceans, measuring changes in sea level and ocean temperatures. • The exchange of heat between the oceans and the atmosphere helps drive our weather. By monitoring ocean currents and temperatures, we can predict the weather. • In the Pacific, satellites reveal the curse of El Nino. It brings heavy rain to South America and drought to Indonesia and Australasia. Eyes in the Sky • Satellites enable vessels to skirt fog banks and heavy seas and to fix navigational positions to within ten meters. Satellites spot the best way through pack-ice and keep track of icebergs. • Monitoring volcanic eruptions - and a global temperature drop as volcanic dust girdles

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the Earth. Tracking industrial emissions and levels of atmospheric gases. The ozone layer, our shield against ultra-violet radiation from the Sun. Above Antarctica, a great hole is revealed in the ozone layer. Chemical emissions are blamed.

Environmental Monitoring • Earth may be warming up. Our eyes-in-the-sky watch the mercury. • They monitor the damage to Earth's environment. • Images from orbit assist with the clean-up after major oil spills. Satellites reveal the environmental cost of war. • They watch the destruction of tropical rainforests - the "lungs" of our planet. Getting the Picture • The SPOT satellite makes for better use of land - with a fresh perspective on urban and rural developments. • By combining images from different positions, SPOT produces 3-D pictures. Then, by adding computer visualizations of prospective developments, their suitability can be assessed. • With satellite radar, we can peer through clouds of volcanic dust and beneath the sands of the Sahara. • False-color imagery provides farm reports from space. • Season by season, satellites monitor the health of crops, alerting growers to pests and blight. • Satellite information shows where pesticides should be sprayed. Background El Nino El Nino is an oceanic and atmospheric phenomenon. It happens in the Pacific Ocean when unusually warm ocean conditions appear along the coasts of Ecuador and Peru. The result can be climatic disturbances of varying severity. El Nino occurs every two to seven years. It can affect weather around the world for months, even years, before patterns suddenly switch back to normal. El Nino, which is Spanish for "the child", refers to the infant Jesus Christ. The ocean current associated with the phenomenon usually begins around Christmas, the season of Christ's birth. And because El Nino is accompanied by a fluctuation of air pressure and wind patterns in the southern Pacific, the phenomenon is correctly known as El-Nino-Southern Oscillation (ENSO). El Nino happens when ocean current are sufficiently warm and persistent to cause a reversal in the usual weather conditions of the eastern and western Pacific. Normally, in the tropical areas of the western Pacific, the waters are warm and the air pressure above them is quite low. Moist air rises, causing the clouds and heavy rain characteristic of south-east Asia and northern Australia. Meanwhile, in the eastern Pacific, the waters are cold and the air pressure high. This creates the arid conditions typical of the western coast of South America. The trade winds blow from east to west, pushing Sun-warmed surface waters westwards and exposing cold water to the surface in the east. During El Nino, however, the easterly trade winds weaken and even reverse. This causes a change in the surface temperature of the ocean. With the wind-change comes an increase in atmospheric pressure. As a result, the warm waters of the western Pacific start to flow back

eastwards and the surface temperatures of the ocean increase significantly off South America. The result is that the normal wet weather of the western Pacific moves to the eastern Pacific. And the usually arid climate of the eastern Pacific moves to the western Pacific. This brings heavy rains to South America and droughts to south-east Asia, India and southern Africa. It can also bring severe weather to large parts of North America. The Ozone Hole The ozone layer lies between 19 and 48 kilometers above Earth's surface. Created by the action of sunlight on atmospheric oxygen, ozone is a form of oxygen that packs three oxygen atoms into each molecule, instead of the normal two. The great benefit of ozone is that it absorbs up to 90 per cent of the harmful ultraviolet (UV) radiation that reaches us from the Sun. Full solar UV radiation can damage crops, marine life and human health. It is, therefore, vitally important that ozone levels are maintained in the atmosphere . Since the 1970s, chlorofluorocarbons (CFCs) have been accused of damaging the ozone layer. CFCs have long been used as refrigerants, in foam plastics and in aerosol cans. When released into the atmosphere, CFCs are broken down by sunlight and the chlorine constituent reacts with and destroys ozone molecules. CFCs have now been banned in many countries but the ozone layer continues to be attacked by bromine halocarbons, nitrous oxide and other chemicals. In 1982, a periodic loss of ozone was detected above the southern polar region. This "ozone hole" develops at the start of the Antarctic spring in early October. After a few months, the hole closes again - but it never disappears completely. By 1995, it covered an area more then twice the size of the USA. More recently, the hole has stretched as far north as the southern tip of South America to inhabited areas. The authorities have warned people to stay indoors during late morning and early afternoon. Research has now shown that the ozone layer is periodically thinning over Arctic regions, although not to the extent as above the Antarctic. Whilst there is a general decline in the amount of ozone throughout the atmosphere, the Antarctic is particularly vulnerable due to the enhancing effect of ice particles in the air and the effects of the wind, especially the south polar vortex. The international response has been to support further research - and to curb the use of ozonedepleting chemicals. The 1985 Montreal Protocol was signed by 49 countries. Its aim was to phase out the use of CFCs by 2000. Scanning the Earth Since the 1960s, our planet has been continuously scanned by a series of Earth resources satellites fitted with high quality cameras and sensors. They have enabled us to see the Earth from a scale and perspective never previously possible. Two kinds of satellite are currently in operation. The first passes over the north and south poles, scanning both the atmosphere and whatever is directly below. These satellites orbit at a height of about 1500 kilometers. During successive orbits, each lasting about 100 minutes, the Earth has rotated by 25 degrees in longitude. This means that at every orbit the satellite conveniently scans a different pole-to-pole strip. The other type of satellite orbits above the equator at an altitude of about 35,900 kilometers. These satellites are geostationary - orbiting at precisely the speed of Earth's rotation and remaining over exactly the same spot. Satellites use remote-sensing to view Earth in both visible light and infrared. Images are interpreted by receiving stations on Earth. By digitizing the images,

computers analyze and manipulate the information beamed from orbit. Colors can be added to highlight differences picked up by the images. For example, "false color" is used to monitor plant growth - to differentiate between healthy plants and those suffering from disease and drought. Remote-sensing detects these differences because plants absorb large quantities of red wavelengths when plants are photosynthesizing normally. As well as monitoring the health of crops and forests, remote sensing helps with map-making and pin-pointing floods, droughts and large-scale fires. Remote-sensing images reveal pollution in the atmosphere and oceans. They plot the movement of icebergs and are even used to locate precious minerals. Weather satellites have greatly improved the accuracy of weather forecasting. In the case of geostationary satellites, they can look at a complete hemisphere of the Earth - useful in viewing cloud formations and global weather systems. Satellites can measure wind speed at sea level and higher in the atmosphere. They can observe the height and the distance between ocean waves. And satellites are invaluable in tracking devastating tropical storms. The idea geostationary satellites was first suggested by Arthur C. Clark in 1945. They have revolutionized communications - relaying everything from phone call to television pictures. Signals can be bounced around the world at the speed of light. By 1997, there were 150 communication satellites in Earth-orbit - and that doesn't include meteorological or scientific satellites. Nor does it include spy satellites. Such satellites eavesdrop on radio messages from thousands of sources across the world. They watch troop movements, track ships and detect submarines. Spy satellites photograph military bases and missile launching sites. Links for Further Information Data and links to Meteosat imagery. http://ftp.csr.Utexas.edu/sst/ A site about El Nino including most frequently asked questions. http://www.usis.it/wireless/wf971021/97102118.htm A theme page about El Nino - with forecasts. http://www.pmel.noaa.gov/toga-tao/el-nino/home.html A general page about the ozone layer. http://www.calidad-del-aire.gob.mx/sima/sima/o3e.html Information about the Upper Atmosphere Research Satellite - images, information and data about its launch and mission. http://uarsfot08.gsfc.nasa.gov/UARS_HP.html Rainforests and link to other sites - news, campaigns, information. http://www.ran.org/ran/ A site about SPOT with images, interpretation of information, programs, production, projects and cartography. http//www.orstom.fr/hapex/spot/spotimg.htm

Questions and Activities for the Curious 1. How do weather satellites help to reduce loss of life from severe tropical storms, such as hurricanes, cyclones and typhoons? 2. Explain how ocean currents play a major role in determining the Earth's weather patterns. 3. What are the probable effects of El Nino on the fishing industries of Peru and Ecuador? 4. If satellites had existed when the Titanic sailed in April 1912, would the liner have sunk? 5. What are the effects of major volcanic eruptions - like Mount Pinatubo in 1991 – on climate, both locally and worldwide? 6. Why is the Antarctic ozone hole largest at the start of Antarctic spring (early October)? 7. What is the role of satellites in assessing the rate at which tropical rainforests are being destroyed? What are the consequences of such destruction? 8. Describe the importance of satellites to farming and agriculture.