THEMATIC MAPPER BANDS
The Landsat MSS (Landsat 1) launched in 1972 imaged the earth’s surface in 4 spectral bands (3 in the visible and 1 in the NIR regions) at a spatial resolution of 79 X 79 m. Based on the success of the Multispectral Scanner, the Thematic Mapper (TM), a second generation sensor for monitoring earth resources was developed for Landsats 4 and 5, launched in 1982 and 1984, respectively. The Thematic Mapper has a better spatial, spectral, and radiometric resolution and extends spectral coverage into the blue, the short-wavelength infrared, and the thermal infrared regions, and is therefore a more sophisticated multispectral sensor.
The Landsat 6 (launched in October 1993) also carried this sensor but failed to attain orbit during launch. Although similar in operational modes to the MSS (which was also part of the Landsat 4 and 5 payloads to maintain continuity), the TM consists of 7 bands that have the following characteristics:
To date, the Landsat TM sensor represents the most sophisticated satellite sensor to provide Earth observation data. The seven spectral bands offers the most comprehensive set of multispectral measurements for land and water surface mapping, monitoring, and analysis.
As can be seen from the table above, the TM sensor has seven spectral bands: Six bands (Bands1-5 and 7) acquire Earth reflectance data, and one (Band 6) acquires Earth temperature data. The spatial resolution of bands in the visible and reflective infrared regions is 30 m, some 2.5 times better than the Multispectral Scanner (MSS). The TM sensor also has greater overall radiometric sensitivity than the MSS.
Six reflectance bands (1-5 and 7) obtain their effective resolution at a nominal orbital altitude of 705 km (438 miles) through an IFOV of 0.043 mrad. The seventh band (but designated as Band 6) is the thermal channel, which has an IFOV of 0.172 mrad, which reduces resolution.
Currently, the TM sensor on Landsat 5 is still collecting data. EOSAT's construction of a Landsat 6 satellite was intended to continue acquisition of TM data with a so-called “Enhanced Thematic Mapper” (ETM). The ETM included the addition of a 15-m panchromatic band to obtain higher spatial resolution. Landsat 6 (as stated above) was lost during launch. The Landsat 7, launched in 1999 carries the ETM.
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