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Monday, 20 December, 1999, 10:37 GMT
Terra leaves the ground

Nasa: Nasa: "Terra has unlimited potential to improve understanding"

The $1.3bn Terra satellite finally got off the ground on Saturday. It had been delayed by a day due to a hang-glider encroaching on the rocket's air space and a faulty sensor triggering a safety warning.

The satellite is the centrepiece of Nasa's Earth Observation System programme which intends to gather unprecedented remote-sensing data of our planet.

Terra satellite
705 km altitude
6.8m length
3.5m wide
5,190 kg weight
2,530 W solar power
Nasa says it will study the land, oceans, air, ice and life to produce "a new global data set on which to base future scientific investigations about our complex home planet".

Terra will orbit the Earth 16 times a day, synchronised with the movement of the Sun. Its path will cross the equator at the same local time every day, about 1030. Observing in the morning minimises the time that clouds obscure the land surface.

The satellite's design has been led by the US, Japan and Canada and includes five instruments for observing the Earth.
  • Measurements of Pollution In The Troposphere (Mopitt) - Analysing global air pollution in the lower atmosphere
  • Clouds and the Earth's Radiant Energy System (Ceres) - Analysing the energy budget of sunlight reaching the Earth and heat leaving it
  • Multi-Angle Imaging Spectroradiometer (Misr) - Analysing how sunlight is reflected from clouds and the Earth's surface
  • Moderate-Resolution Imaging Spectroradiometer (Modis) - Analysing land and ocean surface temperatures and snow and vegetation cover
  • Advanced Spaceborne Thermal Emission and Reflection Radiometer (Aster) - Analysing cloud properties, surface topography and soil properties
Scientists from Oxford University in the UK helped build the Mopitt instrument, the first to be able to detect air pollution in the lower atmosphere from space.

Dr Guy Peskett, from the Department of Atmospheric Physics, told BBC News Online: "We may be able to see plumes of carbon monoxide and methane from cities but the main aim is to get a handle on the chemistry of the troposphere, which is very complex.

Terra has one huge solar panel Terra has one huge solar panel
"And with Mopitt, we also hope to advance the art of the remote sensing of pollutants near the Earth's surface."

Analysing the high atmosphere is relatively easy, as it can be done from the ground, with the blank background of space behind. But to analyse the air near the surface it is necessary to look down on the Earth from above.

"That's a real problem," said Dr Peskett, because there is a lot of background radiation coming from the ground.

The first data from Mopitt is expected in a month. Terra is expected to operate for at least six years, perhaps much longer.

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See also:
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