Eyes in space,
A tool for geographers and
geologists
A new type of agriculture
Protecting the Earth
Green satellites
Digital simulation of public
works
and natural hazard mapping
Flying over the planet
Before the space age, humankind had never been able to take in the whole of a hemisphere in a single glance. In fact it had never had a global view of the world in which it lived. It was not until the first spacecraft went into orbit that our horizons expanded and we saw our planet as never before.
Today, observation satellites are indispensable to scientists, industry and the military, offering each with innumerable reasons to observe the Earth from space in the visible and infrared ranges but also with radar waves which pass through clouds.
Observation satellites are equipped with increasingly efficient viewing systems and are capable of systematically and regularly covering huge territories while producing highly detailed images. This is true for the French satellite "SPOT", which is the reference in civilian remote sensing. It can detect objects of about 10 metres across, within 60 km square images which it acquires from an orbital altitude of 830 km. Its oblique viewing capabilities enable it to acquire both stereopairs, from which the relief of the terrain can be reconstructed, and also repeated observation of the same area without having to fly over the same local vertical. Its specific advantages of offering hindsight based on archives, its detailed imagery, its revisit capability and its flexible programming possibilities make it invaluable for customers, be they national or international bodies or individuals.
United Nations statistics reveal that less than half of the planet's exposed land has been mapped at scales suitable for economic development measures. The need is particularly great for Africa. The answer lies in satellite image maps, which are accurate and can be quickly compiled, which are systematically updated and which cost between one third and one quarter that of airborne remote sensing. "Satellite image maps" have become the mapmaker's benchmark for small and medium scale mapping. The secret behind the unequalled richness of satellite imagery is due to the fact that instead of taking a photograph, their video-type CCD imaging instruments transmit light intensities to the ground. These are then processed by computers to extract the required information for so-called "thematic"maps.
Thematic maps provide large volumes of data on a regional scale whenever needed. This includes data on land-use for town planners or monitoring of population changes, the state or type of vegetation for agricultural inventories, or again geological structures for detecting natural resources or water tables which are often trapped in the vicinity of geological faults.
Earth observation satellites have, moreover, become the precious allies of a new type of agriculture managed from the sky, especially in developing countries where agricultural management is still at an early stage. With a single glance they report on crop areas, identify soil types and inventory water resources. All of which can be used to plan future agricultural development. Likewise, as the season changes, they monitor crop changes and enable early detection of diseases. By averaging yield hypotheses based on field surveys, they can also be used to forecast yields and thus optimize harvest logistics such as agricultural machinery and trucks and the availability of storage silos, etc.
How is it that the world was able to physically see the ripped-open reactor of the Chernobyl nuclear power station, on 29 April 1986, even before any real information on the type of explosion was available? An explosion which had occurred in the Ukraine three days earlier!
The answer : SPOT imagery of the damaged reactor, confirmed for the specialists that they indeed faced a major nuclear accident.
Satellites are an extremely valuable monitoring and decision-making tool, whether this involves detecting a real drama affecting the world, as for Chernobyl, or local pollution due to flushing by an oil tanker at sea. They observe the planet with unequalled efficiency, providing early warning, assessing damage or monitoring a worrisome problem over several days.
Apart from crises, satellite observation has also become one of the best means available to environment specialists for watching the Earth while continuously monitoring threats posed by human activity. Remote sensing satellites are being used today for more efficient assessment, month by month, of the extent of the destruction of tropical forests. Likewise, mapping data provided by SPOT have become indispensable for regularly taking the pulse of those ecosystems which are the most sensitive to human presure or sometimes even to natural pressure. The sky is the best place from which to monitor silting-up of the Venice lagoon or, even the more spectacular drying-up of the Aral sea due to deviation of the rivers flowing into it.
Turning to regional or national development, apart from their monitoring capabilities, satellites can also be used to simulate the effects of public works on the environment, thus making impact studies more efficient. SPOT stereopairs enable engineers to create "digital elevation models", computer-generated images of the landscape incorporating the planned structures, thus showing the whole edifice in its environment, with the possibility of viewing it from any perspective. Even before the first sod has been turned, planners can "see "a highway, a hydro-electric dam or a new railway line as they would fit into the landscape, and even simulate the filling of the dam on a computer. In short, such tools can take environmental constraints into account during planning for development of a given site.
As a simulation tool, satellite imagery can be used to study environmental vulnerability to natural hazards. Comparison of a topographic or digital elevation model with "field" data on past flooding of a large river makes it possible to identify flood-risk areas, thus identifying any structures which might be threatened.
How did it become possible for humankind to move from a regional to a global perspective ?
page updated on the 00-06-06