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History of Remote Sensing: Thematic Mapper (TM)

A more sophistical multispectral imaging sensor, named the Thematic Mapper (TM) has been added to Landsats 4 (1982), 5 (1984), 6 (failed to attain orbit during launch and thus has never returned data) and 7 (1999). These TMs flew on a redesigned, more advanced platform. 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 these characteristics:

Band No. Wavelength
Interval (µm)
Resolution (m)
1 0.45 - 0.52 Blue-Green 30
2 0.52 - 0.60 Green 30
3 0.63 - 0.69 Red 30
4 0.76 - 0.90 Near IR 30
5 1.55 - 1.75 Mid-IR 30
6 10.40 - 12.50 Thermal IR 120
7 2.08 - 2.35 Mid-IR 30

Six reflectance bands obtain their effective resolution at a nominal orbital altitude of 705 km (438 miles) through an IFOV of 0.043 mrad. The seventh band is the thermal channel, which has an IFOV of 0.172 mrad.

Band 1 is superior to the MSS band 4 in detecting some features in water. It also allows us to form quasi-natural color composites. Band 5 is sensitive to variations in water content, both in leafy vegetation and as soil moisture. It also distinguishes between clouds (appearing dark) and bright snow (light). This band also responds to variations in ferric iron (Fe2 O3) content in rocks and soils, which show higher reflectances as the iron content increases. Band 7 likewise reacts to moisture contents and is especially suited to detecting hydrous minerals (such as clays or certain alteration products) in geologic settings. Band 6 can distinguish a radiant temperature difference of about 0.6° C and is helpful in discriminating rock types whose thermal properties show differences in temperatures near their surface. It often can pick out changes in ground temperatures due to moisture variation and can single out vegetation due to its evaporative cooling effect. The higher resolution achieved in the reflective bands is a significant aid in picking out features and classes whose minimum dimension is usually on the order of 30 m (98 ft) . Thus, it can often discern houses and smaller buildings, which were unresolvable in MSS images.

The size and shape of full TM images from Landsats 4 and 5 are identical to the MSS images. At first glance, the quality and characteristics of these full scene TM images seem similar to those made by the MSS after optimal computer-based processing, but on closer inspection they do appear sharper. This apparent similarity is due to the need to resample the TM images for TV monitor displays (which are not high resolution systems capable of reproducing all TM pixels) by dropping some pixels. The influence of the better TM resolution (when un-resampled) becomes apparent whenever photographs of full scenes are enlarged (pictures more than a meter on a side can be produced with exceptional clarity) or subscenes are extracted and enlarged.

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Primary Author: Nicholas M. Short, Sr. email:

Collaborators: Code 935 NASA GSFC, GST, USAF Academy
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