Landsat Multispectral Scanner (MSS) and Thematic Mapper (TM)

Landsat MSS and TM scenes are digital images, like pictures from digital cameras. Each digital image covers a ground area of 185 km x 170 km (115 x 105 miles) and consists of an array of dots called picture elements (pixels) in rows and columns. Every pixel contains numerical values expressing its brightness. Each pixel in an MSS scene represents a 68 m x 82 m ground area, while each pixel in a TM scene represents a 30 m x 30 m ground area (except in the case of the far-infrared band 6 which uses a larger 120 m x 120 m pixel). An ordinary digital camera records only blue, green, and red brightness values corresponding to the range of human vision. The Landsat MSS sensor has 4 bands that simultaneously record reflected radiation from the earth's surface in the green, red, and near-infrared portions of the electromagnetic spectrum. The Landsat TM sensor has 7 bands that simultaneously record reflected or emitted radiation from the earth's surface in the blue-green, green, red, near-infrared, mid-infrared, and the far-infrared portions of the electromagnetic spectrum.

Landsat data have been used by government, commercial, industrial, civilian, and educational communities in the U.S. and worldwide. They are being used to support a wide range of applications in such areas as global change research, agriculture, forestry, geology, resources management, geography, mapping, water quality, and oceanography. The images can be used to map anthropogenic and natural changes on the Earth over periods of several months to two decades. The types of changes that can be identified include agricultural development, deforestation, desertification, natural disasters, urbanization, and the development and degradation of water resources.

The following summary of the Landsat system was derived from the Landsat MSS and Landsat TM on-line user guides published by the U.S. Geological Survey (USGS). These user guides provide detailed information about the Landsat Program and system characteristics, and include diagrams, sample images, and direct links to a glossary of important terms and acronyms. It is important to keep in mind that satellite images can be either classified or unclassified. Classified satellite images differentiate forest cover types as well as other vegetation and land uses. An unclassified satellite image is raw data and can be used as a backdrop in GIS maps with other GIS data layers placed on top.

Technical Background Summary
On July 23, 1972, NASA launched the first in a series of satellites designed to provide repetitive global coverage of the earth's land masses. It was designated initially as the Earth Resources Technology Satellite-A (ERTS-A). When operational orbit was achieved, it was designated ERTS-1. The satellite continued to function beyond its designed life expectancy of 1 year and finally ceased to operate on January 6, 1978, more than 5 years after its launch date. The second in this series of Earth resources satellites (designated ERTS-B) was launched January 22, 1975. It was renamed Landsat 2 by NASA, which also renamed ERTS-1 to Landsat 1. Three additional Landsats were launched in 1978, 1982, and 1984 (Landsats 3, 4, and 5, respectively). Each successive satellite system had improved sensor and communications capabilities.

Landsat 5 was launched in 1984 and is still fully operational. It was placed in a polar (north to south path), sun-synchronous orbit at a nominal altitude of 705 km (438 miles) above the earth. A sun-synchronous orbit ensures that the satellite always passes over the earth at the same local sun time so that sun illumination conditions are consistent. Although sun elevation, relative position, and intensity still vary with the seasons, every Landsat scene has the illumination of the same time of day. The Landsat 5 orbit has an equatorial crossing time of 9:45 a.m. and a return period of 16 days (i.e. every 16 days the orbit path would repeat itself). Landsat 5 carries both the multispectral scanner (MSS) and the thematic mapper (TM) sensors.

The multispectral scanner (MSS) was the primary sensor on Landsats 1-3 and was included on the Landsat 5 platform to provide continuity with previous Landsat data. However, the routine collection of MSS data was terminated in late 1992. The MSS sensor images a swath 185 km (115 miles) wide. Each pixel (picture element) in an MSS scene represents a 68 m x 82 m ground area. This sensor has 4 bands that simultaneously record reflected radiation from the earth's surface in the green (band 1), red (band 2), and near-infrared (bands 3 and 4) portions of the electromagnetic spectrum. The characteristics of the MSS bands were selected to maximize their capabilities for detecting and monitoring different types of earth's resources. For example, MSS band 1 can be used to detect green reflectance from healthy vegetation, and band 2 is designed for detecting chlorophyll absorption in vegetation. MSS bands 3 and 4 are ideal for recording near-infrared reflectance peaks in healthy green vegetation and for detecting water-land interfaces.

The thematic mapper (TM) is an advanced, multispectral scanning, earth resources sensor designed to achieve higher image resolution, sharper spectral separation, improved geometric fidelity, and greater radiometric accuracy and resolution than the MSS sensor. This sensor also images a swath 185 km (115 miles) wide but each pixel in a TM scene represents a 30 m x 30 m ground area (except in the case of the far-infrared band 6 which uses a larger 120 m x 120 m pixel). The TM sensor has 7 bands that simultaneously record reflected or emitted radiation from the earth's surface in the blue-green (band 1), green (band 2), red (band 3), near-infrared (band 4), mid-infrared (bands 5 and 7), and the far-infrared (band 6) portions of the electromagnetic spectrum. TM band 2 can detect green reflectance from healthy vegetation, and band 3 is designed for detecting chlorophyll absorption in vegetation. TM band 4 is ideal for near-infrared reflectance peaks in healthy green vegetation and for detecting water-land interfaces. TM band 1 can penetrate water for bathymetric (water depth) mapping along coastal areas, and is useful for soil-vegetation differentiation and for distinguishing forest types. The two mid-infrared bands on TM are useful for vegetation and soil moisture studies, and discriminating between rock and mineral types. The far-infrared band on TM is designed to assist in thermal mapping, and for soil moisture and vegetation studies.

Landsat MSS and TM Metadata and Other Information Resources:

Land Satellite (LANDSAT) Multispectral Scanner (MSS) - USGS generic metadata for unclassified Landsat MSS data

Land Satellite (LANDSAT) Thematic Mapper (TM) - USGS generic metadata for unclassified Landsat TM data

Minnesota Land Use - Forested Area - Metadata for a 16-class land use/land cover data set derived from Landsat TM satellite imagery for 14 forested counties in northern Minnesota

ImageView is a ForNet application that allows the user to interactively browse more than 10 gigabytes of Landsat TM satellite data covering the entire state of Minnesota. Through a point-and-click map-based interface, users can specify geographic areas of interest and manipulate the display characteristics of the imagery.

ChangeView is a ForNet application that presents browsable "forest change" images, which are derived from two Landsat TM satellite images of the same area on different dates. These images highlight areas of recent, relatively major changes to the forested landscape, including areas of both vegetation loss and gain.

The goal of NASA's Landsat Pathfinder Program is to establish long-term, medium- to high-resolution data sets for particular regional and global applications to global change research.

Current Landsat TM and MSS data is available commercially from EOSAT

TM and MSS data is archived at the USGS's EROS Data Center (EDC)

General technical information on the Landsat Program and the Landsat 7 project is available through the GSFC Landsat Gateway web page