Landsats 4 and 5, launched in 1982 and 1984, respectively, were augmented with an advanced version of an Earth observation sensor known as the Thematic Mapper (TM). The TM provides a significant increase in data acquisition capability over the MSS in a number of ways, as shown in the Figure of Observation Characteristics. The TM sensor has seven spectral bands: Six acquire Earth reflectance data, and one acquires Earth temperature data. The spatial resolution of bands in the visible and reflective infrared regions is 30 m, some 2 1/2 times better than the Multispectral Scanner (MSS). The TM sensor also has greater overall radiometric sensitivity than the MSS.
To date, the Landsat TM sensor represents the most sophisticated satellite sensor to provide Earth observation data. The sensor's complement of seven spectral bands offers the most comprehensive set of multispectral measurements for land and water surface mapping, monitoring, and analysis. Data must be ordered from the Earth Observation Satellite Company (EOSAT), who holds the commercial rights to all TM data less than 10 years old. The U.S. Geological Survey's Global Land Information System (GLIS) provides information on the sensor, and acquisition and availability of Thematic Mapper Landsat Data.
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 was lost during launch, however, when it failed to reach orbit in October 1993.
With passage of The Land Remote Sensing Policy Act of 1992 (Public Law 102-555), development of future Landsat satellites was transferred back to the Federal Government. The National Aeronautics and Space Administration (NASA) is now building Landsat 7, planned for launch in late 1997. This satellite will carry an ETM sensor which includes the 15-m panchromatic band intended for Landsat 6 and the additional improvement of 60-m spatial resolution for Earth temperature data, as illustrated in the Figure of Observation Characteristics. The higher spatial resolution will enable more precise information on widespread land-use changes.