A NASA satellite launched on 18 December 2001 as the flagship for its Earth-observing system. It began collecting data on 24 February 2000 and has exceeded its expected lifespan of 15 years. Terra weighs 5 190 kg and is 6.8 m long. Its instruments include the moderate-resolution imaging spectroradiometer (MODIS), which uses a radiometer to measure biological and physical processes on land and sea; measurements of pollution in the troposphere (MOPITT), provided by the Canadian Space Agency to measure carbon monoxide and methane in the troposphere with a spectroscope; and Japan's advanced spaceborne thermal-emission and reflection radiometer (ASTER) that uses three sensors for images of land, water, ice, and clouds.

http://terra.nasa.gov/ Attractive site presenting images and results from the instruments carried by the Terra Earth-observation satellite. There are galleries presenting the best recent images, as well as background information on climate and land-surface monitoring.