Terra is the flagship of the Earth Observing System, a series of spacecraft that represents the next landmark step in NASA´s role to observe Earth from the unique vantage point of space. Focused on key measurements identified by a consensus of U.S. and international scientists, Terra enables new research into the ways Earth´s land, oceans, air, ice and life function as a total environmental system. Terra was launched into sun-synchronous Earth orbit on December 18, 1999, and started sending data back to earth in February 2000.

Terra carries five scientific instruments: ASTER, CERES, MISR, MODIS, and MOPITT.

MODIS (or Moderate Resolution Imaging Spectroradiometer) is a key instrument aboard the Terra (EOS AM) and Aqua (EOS PM) satellites. Terra’s orbit around the Earth is timed so that it passes from north to south across the equator in the morning, while Aqua passes south to north over the equator in the afternoon. Terra MODIS and Aqua MODIS are viewing the entire Earth’s surface every 1 to 2 days, acquiring data in 36 spectral bands, or groups of wavelengths (see MODIS Technical Specifications).