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Terra: Mission To Planet Earth

A look at the technology behind NASA's new Earth observation satelittes.

By Sammy Isreb

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Since it's beginning in 1958, NASA has focused not just on space exploration but also on the furthering of scientific knowledge regarding planet Earth. With so much unknown about the factors effecting the climate on Earth, NASA embraced Earth System Science, a field encompassing meteorology, oceanography, biology and atmospheric sciences.

In the early 1990s, NASA commenced what is known as the Earth Science Enterprise, a detailed study into the Earth as an environmental system. The Earth Science Enterprise is composed of three main components: a series of satellites, an advanced data storage and processing system and various teams of scientists working to analyse the data.

On the 18th of December 1999, the first of the Earth Observing System (EOS) series of satellites was launched. The Terra satellite, formally known as the EOS AM-1, was built at a cost of over US$1.3 billion by Lockheed Martin Missiles and Space. The 5190kg Terra circles the Earth at an altitude of around 705 kilometres, with a polar orbit of inclination of 98°.

This orbit is specifically designed to descend southwards over the equator at 10:30am (local time), at which time cloud cover is usually at its daily low. Terra orbits the Earth once every 99 minutes. During the 6-year initial duration of Terra, its orbit will be periodically adjusted to maintain its integrity (once per orbit).

Five state-of-the-art instruments make up the scientific payload of Terra. These are used to generate an integrated snapshot of the Earth which is far superior to anything available from previous orbital remote sensing techniques. Dr Grassem Asrarm, NASA's Associate Earth Science Director, commented that Terra "has nearly unlimited potential to improve scientific understanding of global climate change".

Let's now have a look at the five different measurement systems on Terra.

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This map shows the abundance of airborne particulates, or aerosols, over Southern Africa during the period August 14 - September 29, 2000. Low particle concentrations are shown in shades of blue, high concentrations in shades of red. These results were generated from MISR imagery acquired over this time period and processed using MISR's automated software system. The approach for deriving aerosol amount makes use of the variation of scene brightness and contrast as a function of observation angle.

Black areas over the land area correspond to places where a result was not obtained; eg, due to the presence of clouds. Extensive burning of grass and shrubland for land management and agriculture comprises a principal source of these aerosols.

Vegetation availability increases northward, hence the greater abundance of haze and smoke in Angola and southern Zaire. The lower aerosol abundance around Lesotho and southeastern South Africa is consistent with the higher terrain elevations near the Drakensberg Mountains.

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