Looking at Earth


  • Landsat 1

  • Landsat 4

  • Landsat 7

The Landsat satellites have been monitoring the Earth since 1972. Tens of billions of square kilometers of the Earth have been covered by Landsat sensors and this imagery has provided practical information to scientists from many different Earth science disciplines.

Landsat I (originally called ERTS) was launched into an orbit 917 kilometers (570 miles) above the Earth. It made 14 revolutions of the Earth each day and flew over the same spot every 18 days. Succeeding Landsats had the same characteristics until the advent of Landsat 4, launched in 1982. Landsats 4 and 5 were placed in an orbit 705 kilometers (approximately 440 miles) high and repeated their cycle every 16 days. Landsat 4 malfunctioned early in its mission, but Landsat 5 remains operational today.

The Earth-imaging sensor carried on Landsats 1, 2, and 3 was called a Multi-Spectral Scanner (MSS). To Provide continuity with early imagery and allow comparisons of changes in the land through time, Landsats 4 and 5 also carried an MSS. They carried a second more advanced sensor as well, called the Thematic Mapper (TM).

In 1993, Landsat 6 failed to attain its necessary orbit and was lost. In 1999, Landsat 7 began its mission with a new sensor, the Enhanced Thematic Mapper Plus (ETM+).

Multi-Spectral Scanner

The Multi-spectral scanner (MSS) is a sensor that was carried on the first 6 Landsat satellites. It produces images of the Earth that cover an area of about 34,000 square kilometers (about 13,000 square miles) with a resolution of about 80 meters (260 feet). The MSS, which acquires data in both visible and infrared wavelengths, employs an oscillating mirror to scan the Earth beneath the spacecraft.
The Museum's MSS is an engineering model provided by NASA and Santa Barbara Remote Sensing.

Thematic Mapper

The Thematic Mapper is an imaging sensor used on the Landsat 4 and 5 satellites. It can resolve features about three times smaller than earlier Landsat instruments and can collect data in more wavelength bands.
Full-scale model on display in Museum courtesy of Hughes Aircraft Company.

The farmlands of Southern Louisiana (bright green) contrast sharply with the local wetlands in this 1992 Thematic Mapper scene. Nestled between Lake Ponchartrain and the Mississippi River is the city of New Orleans.
Courtesy of EROS Data Center, U.S. Geological Survey

Las Vegas, Nevada. The city of Las Vegas can be seen just west of Lake Mead on this Thematic Mapper scene. One of the largest man-made lakes in the world, Lake Mead was formed by the Hoover Dam on the Colorado River.
Courtesy of ERIM International, Inc.

Enhanced Thematic Mapper Plus

The Enhanced Thematic Mapper Plus (ETM+) is the new sensor flown on the Landsat 7 satellite. The ETM+ has eight bands sensitive to different wavelengths of visible and infrared radiation and has better resolution in the thermal infrared band than the Thematic Mapper (TM) instruments carried by Landsats 4 and 5.
NASA Photograph

Cape Canaveral, the launch site for America's space exploration programs. The Kennedy Space Center (center) and Space Shuttle runway (top) can be seen clearly in this Landsat 7 image. Towards the northeast corner is Launch Pad 39A. Originally designed to support the Apollo program, it was later modified for Space Shuttle launches.
Courtesy of EROS Data Center, U.S. Geological Survey

This ETM+ image from September 1999 reveals the after effects of Hurricane Floyd on the Outer Banks of North Carolina. Flooding from the storm destroyed 7,000 homes and caused severe agricultural damage throughout the eastern portion of the state.
Courtesy of EROS Data Center, U.S. Geological Survey

Flood Effects

This sequence of images, collected by the Landsat Thematic Mapper, illustrates the physical effects of flooding, as seen along the Missouri River in the fall of 1993. During the flood, the river's boundaries are extended, creating wetland areas beyond the active river channel. One month later, water-saturated land can still be seen in the dark blues, blue-grays, and olive greens of the post-flood image. The white to light gray areas reveal the presence of overlying sand deposits.
Courtesy of EROS Data Center, U.S. Geological Survey

The Missouri River in the fall of 1993. This Landsat TM image shows the river before the flood.
Courtesy of EROS Data Center, US Geological Survey

The Missouri River in the fall of 1993. This Landsat TM image shows the river at the peak of the flood.
Courtesy of EROS Data Center, US Geological Survey

The Missouri River in the fall of 1993. This Landsat TM image shows the river after the flood.
Courtesy of EROS Data Center, US Geological Survey


These Landsat scenes vividly illustrate how much damage gypsy moths can inflict on forested regions. The image on the top is a view of an area in Pennsylvania in May 1977. The red color represents healthy vegetation. The picture on the bottom is from July when the gypsy moths have grown to full size. Note how much vegetation has been removed.
Courtesy of D. Williams, Goddard Space Flight Center

These Landsat scenes vividly illustrate how much damage gypsy moths can inflict on forested regions. The red color represents healthy vegetation. This scene is from May 1977.
Courtesy of D. Williams, Goddard Space Flight Center

These Landsat scenes vividly illustrate how much damage gypsy moths can inflict on forested regions. The red color represents healthy vegetation. This scene is from July 1977.
Courtesy of D. Williams, Goddard Space Flight Center


This Landsat image shows cornfields in Kansas planted using a circular irrigation pattern. The blue areas indicate healthy corn while the pink represents areas damaged by lack of water.
Courtesy of Patricia Jaccobberger-Jellison


Landsat images have been used to map sites of possible archaeological interest. Study of this image helped scientists to locate the lost city of Ubar in Southern Oman, on the Arabian Peninsula.
Courtesy of Jet Propulsion Laboratory

Satellite Eyes - Seeing Beyond the Rainbow

Satellites like Landsat can have sensors which "see" in visible light, but they may also be able to record radiation (such as infrared) that it is beyond our capability to see.

The Electromagnetic Spectrum

Visible light is only one kind of electromagnetic radiation that satellites can monitor. Infrared and radar are also part of the electromagnetic spectrum, and each represents radiation in a different wavelength. For example, yellow light has a longer wavelength than blue, and red is longer than yellow. Infrared and radar wavelengths are longer still. By collecting data in different regions of the spectrum, satellites can reveal information that would go undetected by our eyes alone.

Satellite Sensors

The same scene can appear very different when viewed by different satellite sensors. Imagery of California's Imperial Valley illustrates the differences in appearance, coverage, and detail acquired by various orbital missions.

Compare Satellite Images

Apollo 9 view in the visible range. Southern California's Salton Sea is bordered by a patchwork of irrigated crops and farmlands. In contrast to the fertile agricultural region, desert sands of the Algodones Dune Field stretch for 60 kilometers (about 40 miles) to the southeast.
NASA Photograph

Apollo 9 scene taken with color infrared film. In this view, vegetation is indicated by the red color. The straight boundary marking changes in farming patterns is the border with Mexico.
NASA Photograph

This Landsat image of a portion of the Apollo 9 scene uses a combination of near-infrared and visible wavelengths.
Courtesy of U.S. Geological Survey

Thermal infrared image from the Heat Capacity Mapping Mission (HCMM). This scene covers 15 times the area of a Landsat frame but can only resolve features larger than 600 meters (about 1900 feet). The warmest areas of the region, which show up in the lightest tones, are the deserts of Arizona and Mexico. Thermal imagery can reveal important information on the temperature and properties of surface materials.
NASA Image

Radar image from the Seasat mission. The smooth surface of the dune field appears dark, while the rough texture and orientation of the mountains give them a brighter appearance. The light and dark patterns in the Sea are due to variations in the water surface caused by the blowing wind.
NASA Image

Processing An Image

A satellite image is often not a photograph at all. Complex satellite sensors do not record a scene on film, but instead, collect information that can be converted to computer images. The computer scenes are composed of a mosaic of tiny rectangles called picture elements or pixels. By manipulating the image on the computer, different aspects of the terrain can be emphasized.

Digital Images

Digital images are collected as a series of numerical values, each value representing the amount of energy radiated or reflected from a unit of area on the Earth's surface. These images are collected in separate wavelength bands including, and beyond, the region of the spectrum detectable by film systems. Information from each band produces a discrete image from the swath of Earth below the spacecraft. Each image is composed of pixels which can be compared to the squares on a checkerboard. Individual pixel values (numbers representing the relative brightness of each point) are transmitted to a receiving station on Earth to produce the rows and columns of a numerical matrix comprising each scene. Pixels with high values will appear bright. Those with low values will be dark. A color composite image is produced by combining three images into one. Each of the three images of the scene, measured in different wavelengths, is assigned a different primary color: red, green, or blue. The brighter the pixel the more intense the color. When corresponding pixels (the same row and column) from each image are added together, the resulting color is a hue that represents the proportion of red, green, or blue from each of the three original digital images.

A color composite image showing the Washington, DC area.
Images processed at the Center for Earth and Planetary Studies

Numerical values indicate the brightness levels of individual pixels in digital images.
Images processed at the Center for Earth and Planetary Studies

Different wavelengths are assigned to different primary colors and then combined to produce a false color image.
Images processed at the Center for Earth and Planetary Studies

The large image shows a Landsat Thematic Mapper scene of Washington, D.C., including the Potomac and Anacostia rivers. The box indicates the area around the U.S. Capitol building that is enlarged below. Digital images of the Capitol area of Washington, D.C., from three different spectral bands are combined into a false color composite. The colors are called false because any primary color can be assigned to any band. Thus, vegetation can be featured in red by assigning this color to a near infrared band. Vegetation is very reflective in the near infrared and, therefore, has high brightness values in this band.
Images processed at the Center for Earth and Planetary Studies


Another way to look at the land is with radar. Radar "sees" through clouds and does not require the light of day. Imagery can therefore be recorded through poor atmospheric conditions at any time of day or night. The radar image of any feature is dependent upon its physical properties, such as surface roughness, orientation, moisture content, and composition, as well as the wavelength of the radar signal that "illuminates" the scene.

The San Andreas Fault extends from the upper left to the lower right on this radar image from the Seasat satellite which operated in 1978. The smooth surface of the Mojave Desert northeast of the fault appears dark, while the rugged San Gabriel Mountains to the southwest have a bright signature. The major roadways of the San Fernando Valley are clearly indicated at the lower right.
NASA Image

Seasat radar view of the folded Appalachian Mountains.
NASA Image

Shuttle Imaging Radar

The first Shuttle Imaging Radar instrument (SIR-A) was flown on the Space Shuttle in 1981. It acquired imagery of around 10 million square kilometers of the Earth's surface.

Landsat image of the Western Desert of Egypt showing the location of the SIR-A overlay.
Courtesy of G. Schaber, US Geological Survey

Shuttle Imaging Radar Experiment (SIR-A) data overlayed onto a Landsat image of the Western Desert of Egypt shows ancient dried up river channels.

A strip of data from the first Shuttle Imaging Radar Experiment (SIR-A) has been superimposed on a Landsat image of the Western Desert of Egypt. Ancient dried up river channels (wadis), often covered by a layer of sand, are delineated much more clearly on the radar imagery. Identification of wadis, where water once flowed freely, helps archaeologists to locate ancient sites of human habitation.

The third in the series, SIR-C/X-SAR (Spaceborne Imaging Radar-C/X-band Synthetic Aperture Radar) was flown in the cargo bay of the Space Shuttle Endeavour twice in 1994. The SIR-C/X-SAR antenna is 12 meters (almost 40 feet) long and 4 meters (13 feet) wide. During the SIR-C/X-SAR missions, scientists on the ground collected data at targeted sites in order to correlate ground characteristics with the data collected from orbit.

Courtesy of G. Schaber, US Geological Survey

This 3-D view of the Alcedo Volcano on Isabela, one of the Galápagos Islands, was created by overlaying topographic data with SIR-C/X-SAR radar imagery. In this image the radar data helps to delineate different volcanic features. The rougher textured lava flows appear as bright features, while smoother ash deposits and lava flows appear darker.
Courtesy of Jet Propulsion Laboratory


RADARSAT, launched in November 1995, is operated by the Canadian Space Agency and provides radar data in a variety of resolutions.

The Bear Peninsula (left) and the ridged terminus of the Thwaites Glacier (lower right) jut out into Antarctica's Pine Island Bay in this image collected by the RADARSAT spacecraft. The image was acquired as part of the joint Canadian/U.S. Antarctic Mapping Mission (AMM). The AMM, begun in Sept. 1997, is a program to map the entire continent of Antarctica from space at high resolution. More than 8000 radar images of Antarctica have been compiled into a detailed map of the icy Antarctic.
RADARSAT data © Canadian Space Agency/Agence spatiale canadienne, 1997. Data received by the Canada Centre for Remote Sensing. Processed and distributed by RADARSAT International. Printed by Imagetech Resource Laboratories (Montreal).