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Mission


The Landsat program consists of a series of U.S. satellites designed to acquire high resolution remotely sensed images of the Earth's land surface and surrounding coastal regions. For more than 25 years, these satellites have provided detailed observations about the surface of our planet. Agricultural evaluations, forest management inventories, geological surveys, water resource estimates, coastal zone appraisals, and a host of other applications have been performed with Landsat data to meet the needs of business, government, science and education and national security.


Data from Landsat is used for monitoring population changes in and around metropolitan areas, monitoring global deforestation and fire damage, estimating soil moisture and snow water equivalence, and monitoring flood, storm, earthquake and volcanic eruption damage. Additional applications include studies of tropical deforestation, timber losses in the U.S. Pacific Northwest, soil moisture and snow water. The success of Landsat has established the United States as the world leader in land remote sensing and contributed significantly to our understanding of the Earth's environment.


With the 1999 launch of Landsat 7, the Landsat program's most recent addition, the program became part of a global research program known as NASA's Earth Science Enterprise, a long-term program that is studying changes in Earth's global environment. The goal of the Earth Science Enterprise is to provide people with a better understanding of natural environmental changes using a fleet of satellites, each designed to target a specific component of our environment. Landsat's primary role is to provide global, high-resolution measurements of land surface and surrounding coastal regions. All of the Earth Science Enterprise data will be distributed to researchers worldwide and will become an essential tool for making informed decisions about our environment.


History


In the mid to late 1960's NASA recognized the potential of using space technology to study the Earth's environment and initiated efforts to develop a program for remote sensing of earth resources from space. The objective of this program was to gather data about natural resources from earth observing satellites carrying remote sensing instruments. As a result the Earth Resources Technology Satellite (ERTS) was launched by NASA in July, 1972. The ERTS satellite, later re-named Landsat 1, marked the beginning of nearly three decades of the Landsat program, which continues to build a photographic record of our changing planet that is unmatched by any other research program in history.


Landsat 1 carried a television camera and an experimental sensor called the Multi-Spectral Scanner (MSS). This sensor was developed following several years of studies with airborne multispectral scanners, which provide scanned data of the Earth's surface in different portions of the electromagnetic spectrum. During its operational lifetime, Landsat 1 acquired over 300,000 images of the planet and established a rich set of data about global land surfaces that exceeded all expectations. The MSS proved so valuable and successful that it was included on the next four Landsat satellites, including Landsat 2, launched in January, 1975 and Landsat 3, launched in March, 1978. The historical record created by the early Landsat satellites forms the basis of comparison used to detect and measure change on our planet's surfaces.


Landsat 4, launched in July, 1982, carried a newly improved multispectral sensor called the Thematic Mapper, which marked the beginning of a second generation of remote sensing satellites. The Thematic Mapper added three new spectral bands and provided improved resolution of 30 meters (compared to the MSS resolution of 80 meters). Landsat 5, launched in March, 1984, also carried the Thematic Mapper and remains in limited operation today, continuing to contribute to Landsat's historical archive of images of the Earth.


In 1985, operation of the Landsat program was commercialized and the Earth Observation Satellite Company (EOSAT) assumed responsibility for operation of Landsat 4 and 5, managed the distribution of Landsat data, and built two new spacecraft (Landsat 6 and 7). Landsat 6 was launched in October, 1993 but failed to reach orbit and was lost. This satellite carried an improved version of the Thematic Mapper known as the Enhanced Thematic Mapper (ETM), which would have provided improved resolution and accuracy.


Landsat 7


The operation and distribution of data for new Landsat satellites was placed back into the federal government hands with the Landsat 7 satellite, which is currently maintained by a joint NOAA/NASA/USGS task force. When Landsat 7 was launched in April, 1999 it signaled a new era for Landsat with a new mission and a new sensor called the Enhanced Thematic Mapper Plus (ETM+).


Artist Rendition of Landsat 7 in Orbit
 
Figure 1. Artist Rendition of Landsat 7 in Orbit

The ETM+ provides 7 channels in the visible, near, mid, and thermal infrared channels, along with a 15 meter resolution panchromatic sensor. Landsat 7 also included improvements such as increased storage and data transmission capabilities which dramatically increase the number of images that can be obtained and stored each day.


Landsat 7 Being Prepared for Launch
 
Figure 2. Landsat 7 Being Prepared for Launch

The spectral resolution of each of the 7 bands, plus the panchromatic band, are summarized in the following table, along with a description of the spatial resolution and the primary use of data in each band:


Band Spectral Range (microns) Electromagnetic
Spectrum
Component
Ground Resolution
(meters)
Uses
1 0.45 - 0.52 Visible blue-green
(reflected)
30 Band 1 is useful for mapping water near coasts, for differentiating between soil and plants, and for identifying manmade objects such as roads and buildings.
2 0.53 - 0.61 Visible green
(reflected)
30 Band 2, which spans the region between the blue and red chlorophyll absorption bands, shows the green reflectance of healthy vegetation. It is useful for differentiating between types of plants, for determining the health of plants, and for identifying manmade objects.
3 0.63 - 0.69 Visible red
(reflected)
30 Band 3 is one of the most important bands for discriminating among different kinds of vegetation. It is also useful for mapping the boundaries of soil and rock types.
4 0.75 - 0.90 Near Infrared
(reflected)
30 Band 4 is especially responsive to the amount of vegetation biomass present in the scene. It is useful for crop identification, for distinguishing between crops and soil, and for identifying the boundaries of bodies of water.
5 1.55 - 1.75 Mid-Infrared
(reflected)
30 Band 5, a reflective infrared band, is sensitive to turgidity--the amount of water in plants. Turgidity is useful in drought and plant vigor studies. In addition, Band 5 can be used to discriminate between clouds, snow, and ice.
6 10.40 - 12.50 Thermal Infrared
(emitted)
60 Band 6 measures the amount of infrared radiant flux (heat) emitted from surfaces. Band 5 helps to locate geothermal activity, to classify vegetation, to analyze vegetation stress, and to measure soil moisture.
7 2.09 - 2.35 Mid-Infrared
(reflected)
30 Band 7 is particularly helpful for discriminating among rock types.
Pan 0.52 - 0.90 Visible light
(reflected)
15  

Table 1. Spectral Resolution and Related Information for Landsat 7 Bands

Landsat Bands


Landsat Band 1 for Howard County, Maryland
 
Figure 3. Landsat Band 1 for Howard County, Maryland

Band 1. The spectral response of Band 1 is in the Visible portion of the electromagnetic spectrum that corresponds with blue-green light. Energy at this portion of the electromagnetic spectrum is easily scattered by particles in the atmosphere, often giving images in this band a hazy appearance. This band is capable of being transmitted through water and is especially sensitive to particles suspended in water (such as sediments and algae). Data from this band can be used with bands 2 and 3 to create "true" color composite images, which most closely approximate how the scene would appear to the human eye.


Landsat Band 2 for Howard County, Maryland
 
Figure 4. Landsat Band 2 for Howard County, Maryland

Band 2. The spectral response of Band 2 is in the Visible portion of the electromagnetic spectrum that corresponds with green light. It can be used with bands 1 and 3 to create "true" color composite images.


Landsat Band 3 for Howard County, Maryland
 
Figure 5. Landsat Band 3 for Howard County, Maryland

Band 3. The spectral response of Band 3 is in the Visible portion of the electromagnetic spectrum that corresponds with red light. It is also one of the three component bands used to create "true" color composite images.


Landsat Band 4 for Howard County, Maryland
 
Figure 6. Landsat Band 4 for Howard County, Maryland

Band 4. The spectral response of Band 4 is in the Near Infrared (NIR) portion of the electromagnetic spectrum. This form of infrared sits just outside the visible red light portion of the electromagnetic spectrum. The radiation is reflected to a high degree by leafy vegetation since chlorophyll (the green pigment in green vegetation) reflects much of the NIR that reaches it.


Landsat Band 5 for Howard County, Maryland
 
Figure 7. Landsat Band 5 for Howard County, Maryland

Band 5. The spectral response of Band 5 is in the Middle Infrared (Mid-IR) portion of the electromagnetic spectrum. This portion of the spectrum is sensitive to variations in water content in both leafy vegetation and soil moisture. This band allows an observer to distinguish between clouds (which appear dark) and bright snow cover (which appears light). Sensors in this band also respond to variations in ferric iron (Fe2O3) in rocks and soils, showing higher reflectance as iron content increases. This allows one to use these data to determine mineral content and soil types from space.


Landsat Band 6 for Howard County, Maryland
 
Figure 8. Landsat Band 6 for Howard County, Maryland

Band 6. The spectral response of Band 6 is in the Thermal Infrared portion of the electromagnetic spectrum. Thermal infrared is radiation that is detected as heat energy, therefore the thermal IR band effectively measures the temperature of the surfaces it scans. Band 6 on the ETM+ sensor can distinguish temperature difference of about 0.6 Celsius, which allows it to detect relatively small differences in land and water surface temperatures. This makes the thermal IR band useful for a variety of purposes. For example, using band 6 data, researchers can discriminate among rock types whose thermal properties show differences in temperature near the surface. This assists researchers in creating geologic mapping of land surfaces from space. This data supports agricultural and mineral exploration efforts. Band 6 data can detect changes in ground temperature due to moisture variations, assisting in drought planning, flood forecasting, and agricultural assessment. The cooling effect of water evaporating from vegetation can be detected, assisting in efforts to map land use characteristics of a region.


Landsat Band 7 for Howard County, Maryland
 
Figure 9. Landsat Band 7 for Howard County, Maryland

Band 7. The spectral response of Band 7 is in the Middle Infrared (Mid-IR) portion of the electromagnetic spectrum. This portion of the electromagnetic spectrum is sensitive to moisture and thus responds to the moisture contents in soils and vegetation. The sensitivity to moisture contents is suited to detecting certain water-loving minerals, such as clays, in geologic settings. This band is also useful in detecting moisture levels in leafy vegetation, which can change under certain environmental conditions (e.g. drought, pollution, insect infestation) and thus provides a means to monitor productivity and identify agricultural areas that are under stress.

Panchromatic Band (Landsat 7 Only). 0.52 to 0.90 picometers black and white sensor with a 15 meter spatial resolution. The higher resolution of this data assists land-use researchers by making identification of smaller objects easier. Items smaller then 30 meters will appear fuzzy or ill defined in the 30 meter bands of the ETM+ sensor. The 15 meter resolution of the panchromatic band will allow researchers to make better determinations of land cover and will assist in producing accurate land cover maps of a region.


Panchromatic Band for Howard County, Maryland
 
Figure 9. Panchormatic Band for Howard County, Maryland

References



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