The first satellite to be designed specifically for observing the Earth's surface was called ERTS-1 (Earth Resources Technology Satellite-1). It was later renamed LANDSAT.
The US Geological Survey wanted to obtain information about rocks and geological structures. The US Department of Agriculture needed information for increased efficiency in managing, monitoring and forecasting in the agricultural sector. It proved to be a very successful mission, producing images which were useful not only for agriculture and geology, but for numerous other applications.
Several LANDSAT satellites have been operated since the launch of ERTS-1 on 23rd July 1972. The LANDSAT 4 and LANDSAT 5 satellites carried a multispectral scanner (known as MSS) and another multispectral scanner, called the Thematic Mapper (TM). LANDSAT 5 is expected to remain operational until the year 2000. LANDSAT 7 was launched on 15th April 1999 and carries a sensor known as the Enhanced Thematic Mapper Plus (ETM+).
LANDSAT 6 failed to achieve orbit.
Landsat Multispectral Scanner (MSS)
Landsat Thematic Mapper (TM)
The Thematic Mapper is an optical sensor carried on board LANDSAT 4 and LANDSAT 5. It detects reflected sunlight and emitted heat energy from the Earth's surface. It collects the information in lines across the satellite path (185 km on the ground), as the satellite moves along the orbital path. A rotating mirror synchronised with the satellites' forward motion collects data on both the forward and backward scans. The system is designed so that the movement of the mirror fits in with the movement of the platform so that each strip is next to the previous one.
Energy coming from the Earth's surface hits the mirror and is directed through a series of optical lenses and onto a bank of detectors. Before the energy reaches the detectors it is split into a number of different wavelength bands. TM is therefore known as a multispectral sensor. It detects energy across seven wavelength bands. Photoelectric detectors are used for six of the wavelength bands but heat sensitive detectors must be used for recording the thermal infrared energy.
The pixel resolution of six of the wavelength bands is 30 metres but the thermal infrared band has a pixel resolution of 120 metres.
Landsat Enhanced Thematic Mapper Plus (ETM+)
This instrument is carried on LANDSAT 7. Data are collected from the instrument in different ways so that a number of types of images can be produced. The wavelength bands include:
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