Landsat Program
History
Originally known as the Earth Resources Technology Satellite (ERTS) Program, the Landsat program was established in the early 1970s. The program was conceived as a collaboration between the National Aeronautics and Space Administration (NASA), the United States Geological Survey (USGS), and the
National Oceanic and Atmospheric Administration (NOAA) (NOAA). The primary goal of the Landsat program was to provide a space based remote sensing platform that could provide low cost imagery of the entire earth. Availability of data was to be unrestricted and focused on land resource study.There have been five operational Landsat satellites, offering continuous earth coverage from 1972 to present. The graph below illustrates the operational life span of Landsats one through five.
As is clear from the graph above, Landsats four and five are still operational, though Landsat four has diminished functionality. Additionally, as the list below shows, although Landsat six was launched, it did not achieve successful orbit and was never operational.
Sensors
Landsat satellites function by orbiting the earth in an overlapping pattern that covers every spot on the earth every 18 days(Landsat 1,2,3) or 16 days (Landsat 4,5).
The only sensor onboard, which offers continuous data collection since 1972, is the Landsat Multispectral Scanner (MSS). Though the early Landsat satellites also carried a Return Beam Vidicon (RBV) sensor on board, this was replaced on Landsats 3, 4, and 5 by the Thematic Mapper (TM) sensor. The MSS functions by focusing the imagery from the ground, by way of a rotating mirror, onto a series of photosensors as the satellite orbits the earth.
These radiance levels are recorded by the photosensor array in four different bands representing the green, red, near infrared, and middle infrared (see below). The resolution afforded by the MSS is nominally 60 to 70 meters.
