The Earth-Sensing Legacy
NASA pioneered the first remote-sensing Earth satellites with the
"Landsat" series. The first of these spacecraft, originally called ERTS
(Earth Resources Technology Satellites), was launched on July 23, 1972.
Landsat 4, a second-generation Landsat satellite, was launched on July
16, 1982, followed by Landsat 5 on March 1, 1984. Landsat 5, which is
still providing data, contributed to the production of the first
composite multispectral (multiple spectral bands) mosaic of the 48
contiguous United States.
Landsat 7, launched on April 1, 1999, is designed to extend and improve
upon the more than 25-year record of images of Earth's continental
surfaces provided by the earlier Landsat satellites. The continuation of
this work is an integral component of the U.S. Global Change Research
Program. Landsat 7 is providing essential land surface data to a broad,
diverse community of national security, civilian, and commercial users.
Enter EO-1
Future NASA Earth-observing spacecraft will be an order of magnitude
smaller and lighter than current versions, thus saving millions of
dollars in launch costs alone. The EO-1 mission will provide the
on-orbit demonstration of six revolutionary spacecraft technologies
which if successful, will enable future Earth and space science missions
to be conducted using smaller, lower weight and reduced power spacecraft
buses.
EO-1 will also demonstrate three advanced land-imaging instruments,
each having unique filtering methods for passing light in only specific
wavelengths of radiant energy, called "spectral bands." EO-1 spectral
bands will allow researchers to best look for specific surface features
or land characteristics based on scientific or commercial applications.
These advanced imaging instruments will lead to a new generation of
lighter weight, higher performance, and lower cost Landsat-type imaging
instruments for NASA's Earth Science Enterprise.
The centerpiece of this mission is the Advanced Land Imager (ALI)
instrument. This new instrument will demonstrate remote-sensing
measurements of the Earth that are consistent with data collected by the
Landsat series of satellites. These data are used by farmers, foresters,
geologists, economists, city planners, and others for resource
monitoring and assessment. ALI will lay the technological groundwork for
future land-imaging instruments to be more compact and less costly. A
Landsat-style instrument based on ALI would have a mass of 106
kilograms, consume only 118 watts of power while performing scans,
occupy a volume of .25 cubic meters, and possess finer spectral coverage
over the current Landsat 7 imager, the Enhanced Thematic Mapper Plus
(ETM+). In comparison, the ETM+ has a mass of 425 kilograms, consumes
590 watts of power while performing scans, and occupies a volume of 1.7
cubic meters. Earth Observing-1
Advanced Technologies
Related EO-1 Links
EO-1 Home Page
EO-1 In Depth with Images & Movies
Landsat 7 Project Page
Sensors aboard the Landsat satellites were built in a "whisk broom" (across track) configuration. In a whisk broom sensor, a mirror scans across the satellite's path, reflecting light into a single detector which collects data one pixel at a time. The moving parts make this type of sensor expensive and more prone to wearing out.
Data from the ALI might help ranchers identify the most suitable lands
for livestock grazing, or help farmers improve crop yields by
identifying areas that need additional fertilizer or irrigation.
EO-1 will also carry an advanced high-resolution hyperspectral
(capable of resolving a large number of spectral bands per pixel)
imager, called Hyperion. Hyperion will be capable of resolving 220
spectral bands at wavelengths from 0.4 to 2.5 micrometers with a
30-meter resolution (i.e., the smallest object observed will be 30m x
30m). This is a vast improvement over the current Landsat technology,
which supports only eight multispectral bands at a similar resolution.
Because of the large number of spectral bands on Hyperion, complex land
ecosystems can be imaged and more-accurately classified. A "pushbroom" (along track) sensor like ALI consists of a line of sensors arranged perpendicular to the flight direction of the spacecraft. Different areas of the surface are imaged as the spacecraft flies forward. Pushbroom sensors are generally lighter and less expensive than their whisk broom counterparts, and can gather more light
because they look at a particular area for a longer time, like a long exposure on a camera. One drawback of pushbroom sensors is the varying sensitivity of the individual detectors. (Animations by Robert Simmon)
For example, detailed classification of land assets will enable
improved remote mineral identification and hazardous waste monitoring.
Researchers estimate that there may be more than 20,000 active and
abandoned mines in the western U.S. alone. It is a daunting task to use
field methods alone to inventory and assess how acidic drainage from
mines affects surface water quality and impacts the environment. EO-1
will help land resource managers greatly accelerate this inventory.
The third instrument on EO-1 is the Atmospheric Corrector. Earth
imagery from space is often degraded by the absorption and scattering of
solar radiation due to the aerosol and water vapor content of the
atmosphere (analogous to looking through a dirty window). The
Atmospheric Corrector is a moderate spatial resolution (250 meters)
imaging spectrometer with a 185-kilometer (115 mile) swath, the same as
Landsat 7's ETM+. Using the Atmospheric Corrector, instrument
measurements of actual, rather than modeled, absorption values will
enable more accurate measurement and classification of land resources
and better models for land management in the future. Additionally NASA
will provide its Atmospheric Corrector technologies to U.S. industry with
the explicit purpose of expediting technology transfer to the commercial
sector. Hyperion, the hyperspectral imager on EO-1, will measure much finer spectral information than the ETM+ or ALI. In nature, spectral information is continuous - the amount of sunlight reflected off a point on the Earth's surface varies smoothly with changes in wavelength. Hyperion's 220 bands (green line) provide a more accurate depiction than the discrete bands of Landsat (blue dots). (Graph by Robert Simmon)
This true-color image of Houston, Texas, (acquired by the Moderate-resolution Imaging Spectroradiometer) was not corrected for the effects of the atmosphere. Note the blue tone of the image, and the overall brightness.
For each scene, EO-1's three sensors will collect more than 20
gigabits (20 trillion bits) of data that are stored at high rates on the
on-board solid state recorder. When the EO-1 spacecraft is in range of a
ground station, the spacecraft will automatically transmit its recorded
image to the ground station for temporary storage. The ground station
will store the raw data on digital tapes which will be forwarded to
NASA's Goddard Space Flight Center for processing and sent to the EO-1
science and technology teams for validation and research purposes.
next: Advanced Technologies
back: Introduction
This image is based on the same data as the image above, but the red, green, and blue channels have been corrected for the scattering that occurs as light passes through the atmosphere. The Atmospheric Corrector aboard EO-1 will allow scientists to improve their data even further, a necessity for the precise measurements made by EOS sensors. (Images courtesy Jacques Descloitres, MODIS Land Team)
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