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Landsat
Orbit
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The Landsat satellites have repetitive, circular, sun-synchronous, near-polar orbits, providing full coverage between 81°N and 81°S. The sensors always scan the ground at satellite nadir. The sun-synchronous orbit means that all acquisitions over a given area occur at the same time, giving consistent shadows for the time of year. The equatorial crossing time during descending passes (ascending passes are at night) is, for all Landsat Missions, between 9:30 and 10:00 local time.
A Landsat track is 183km wide. The repeat cycle for Landsat 4,5 & 7 is 16 days. Landsat 7 was launched on April 15, 1999, and orbits 8 days behind Landsat 5.
Sensors
Landsats 1—3 carried the Return Beam Vidicon (RBV) camera and the Multispectral Scanner (MSS). The second generation of Landsat satellites, beginning in 1982 with Landsat 4, carries a Thematic Mapper (TM) in addition to the MSS. Landsat 7 is equipped with an Enhanced Thematic Mapper, ETM+.
ETM+ brings a number of advantages over its predecessor, with a Panchromatic band with 15 metres resolution intrinsically registered with the multispectral bands, while the resolution of the thermal infrared has improved to 60m. There is an on-board Solid State Recorder (SSR) with 378 Gb (500 full scenes) of data capacity.
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