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Watchful eyes in space

The coming of age of Earth observation satellites

The beautiful, spiralling white mass on a blue background looks like an abstract painting – but no human artist has been at work here. The swirling cloud pattern was photographed from space and TV viewers have seen many others like it, whenever a hurricane storm somewhere in the world has been in the news. And yet the very first time that meteorologists were able to observe this typical cloud formation from above was not so long ago. On 5 October 1954, a US Navy rocket was launched into the sky from White Sands in New Mexico.

A journey to the edge of space © Airbus Defence and Space

It rose to an altitude of 160 kilometres and, when it reached the apogee of its flight, the two 16-millimetre film cameras on board shot a series of photos of the ground below. By today’s standards, the pictures might seem pale and out of focus, but at the time the scientists were very excited, because they could immediately see the huge potential of space-based images as a means of advancing weather research and forecasting techniques.

A journey to the edge of space © Airbus Defence and Space

 

This first experimental rocket flight was quickly followed by permanently stationed Earth-orbiting satellites, such as the American TIROS satellite that broadcast the first-ever TV images of Earth from space, on 1 April 1960. By the end of 1977, Europe also had its own first weather satellite in space, Meteosat-1 (built by Airbus Defence and Space’s predecessor Aerospatiale). 

Image on the right: First television image of the Earth from space. Taken by TIROS-1 (1 April 1960).© NASA

The adventure that started with NASA’s ‘Mission to Planet Earth’, as the Earth observation research programme launched by the National Aeronautics and Space Administration in the early 1980s was called, has since grown into one of the largest and most complex space projects ever undertaken.

First television image of the Earth from space. Taken by TIROS-1. © NASA

Today, there are more than 1,000 remote-sensing satellites circling the Earth at different altitudes and in different orbits. Not only does their elevated vantage point give them an unprecedented view of events on Earth, the advanced sensors they carry on board also enable them to capture data in regions of the electromagnetic spectrum that are invisible to the human eye.

Whereas humans are only capable of sensing colours and degrees of brightness in the narrow band of frequencies with wavelengths between 0.4 and 0.8 micrometres (blue and red respectively), the ‘eyes’ of a satellite such as Envisat, the European flagship designed and built by Airbus Defence and Space and launched in 2002, can also detect light in the ultraviolet, infrared and microwave regions of the spectrum.

Envisat: Europe’s largest and most complex Earth observation satellite, the ENVIronmental SATellite, Envisat, was launched in 2002 by an Ariane 5 into an 800-km polar orbit. © Airbus Defence and Space

And in the same way as the different shades of green in the woodland canopy tell us about the health of a forest, we can also gather important data on the basis of the wavelengths or ‘colours’ of invisible light. For instance, the intensity of infrared light emitted by an object at a wavelength in the thermal imaging region of 11 micrometres allows us to calculate its temperature.

Envisat: Europe’s largest and most complex Earth observation satellite, the ENVIronmental SATellite. © Airbus Defence and Space


This same principle is used by satellites orbiting 800 kilometres above the Earth to measure the surface temperature of the oceans to an accuracy of 0.5° Celsius, thus providing important data not only to meteorologists but also to climate researchers, marine biologists and the fishing industry.

It is also thanks to Earth observation satellites that the ozone hole was first discovered. When the American satellite Nimbus 7, which was launched in 1978, detected exceptionally low concentrations of ozone in certain parts of the stratosphere, these were initially interpreted as a measurement anomaly and automatically corrected to a higher value. It was only later, when measurements obtained by research stations in Antarctica indicated that the ozone layer was being depleted, that the Nimbus data were re-examined and proved to be entirely correct.

The correct interpretation of data delivered by remote-sensing satellites will continue to be an issue that preoccupies researchers. Each new question will inevitably lead to improved sensors and new satellite missions. But there is no doubt that remote-sensing satellites have long since come of age.

Successful missions such as ERS-1 and ERS-2 (both under the system management of Airbus Defence and Space’s predecessor DASA) and Envisat have paved the way for Europe’s future GMES (Global Monitoring for Environment and Security) system, which is scheduled to go fully operational in 2014/2015, to make remote-sensing data a natural part of everyday applications. 

This was the first ever image taken by ERS-1 on 27 July 1991 of the Frisian Islands in the The Netherlands. © ESA

This was the first ever image taken by ERS-1 on 27 July 1991 of the Frisian Islands in the The Netherlands. © ESA

The system consists of a finely orchestrated group of instruments, comprising sensors of all imaginable types, designed to scan the Earth’s land masses, oceans and atmosphere in repeated cycles. They will provide a rolling global survey of the state of the environment and the natural cycles that influence the climate, enabling information packages to be put together to meet the needs of a wide range of users and delivered as GMES services.

For this is the great advantage of satellite-based remote sensing: every point on the Earth is monitored at regular intervals, the length of which varies according to the number of satellites and their orbit.

Low-ozone event over Northern Hemisphere © ESA

The data obtained in this way are not only of inestimable value to weather and climate researchers but also form the basis of new information services of interest to farmers, the fishing industry, archaeologists and many other users. Images from the watchful eye in space, updated on a regular basis, help relief organisations to plan rescue missions in areas struck by a natural disaster, and provide worried citizens, anxiously following the progress of a swirling white cloud on the TV news, with sufficient time to take shelter.

Low-ozone event over Northern Hemisphere © ESA

 

 

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