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For more than 10 years, NASA Landsat satellites have been
recording pictures of the Earth's surface. Landsat 1, the first
satellite in this series, literally changed the way we looked at our
planet. Instead of returning exposed film it transmitted an
astounding stream of numbers. Through its complex optical system, the
Earth's surface was broken into narrow slices or scan lines. While
moving roughly north to south over the sunlit side of Earth a mirror
directed Earth's reflected light from the east/west sending scan lines
into detectors. Before reaching the detectors, the light was broken
down into spectral bands, two in the near infrared region invisible to
the human eye and one each in the red and green light. Furthermore
each scan line was subdivided into individual segments 79 by 79 meters
in size so that the reflected light levels of acre-sized plots of land
could be recorded. Back on Earth, the streams of numbers received
from Landsat 1 were assembled by a computer into black and white
images, either of the color bands, or "false color" images. Using
false colors, healthy vegetation can be made to stand out in bright
red, while diseased or insect-infested plants appear gray. To make
just one colored view, more than six million pieces of Landsat 1 data
had to be assembled. Once assembled, the data could be manipulated.
Unusual or unique combinations of reflected light levels could be
intensified by computers to reveal features and trends on the Earth's
surface not readily apparent to the human eye alone. When combined
with observations made on the ground itself, Landsat 1 data could be
processed into land-use classification maps.
The first three Landsat satellites, launched in July 1972,
January 1975, and March 1978, were basically similar in function.
These satellites are no longer in service. Landsat 4, launched July
16, 1982, and Landsat 5, launched March 1, 1984, are "second
generation" spacecraft, with both the multi-spectral scanner and a new
instrument called the "thematic mapper." In its first few days of
operation the mapper demonstrated its ability to produce data of such
detail and clarity that its use represents a major advance in Earth
observations from space.
Landsats 1, 2, and 3 have enabled agricultural interests in
the United States and other nations to inventory fields of different
crops in a fraction of the time this task would require by other
means. For example, investigators used Landsat images of California's
Imperial Valley to count more than 25 separate crops in 8,865 fields
covering 458,000 acres in only 45 manhours.
This experiment and others demonstrated the potential of
satellite systems for swift and frequent crop inventories of the sort
that are fundamental to accurate crop forecasting. Good forecasts are
a big help in planning the amounts of labor, fuel, and transportation
needed for crop harvesting and distribution.
In another experiment NASA, the Department of Agriculture,
and the National Oceanic and Atmospheric Administration used Landsat
in support of a large area crop project. This was to demonstrate the
ability of a satellite system to help forecast the production of an
important world-wide crop, in this case wheat. The total wheat
average was calculated from Landsat surveys. The potential yield per
acre was determined on the basis of regional weather forecasts, and
past meteorological data showing how much wheat grew in that region
under the expected weather conditions. The regional forecasts were
then added together to obtain a figure for the entire world.
The ability to obtain timely crop area estimates can lead to
a world-wide crop forecasting system. This would offer significant
potential benefits. As an example, according to a study performed
recently, a 25 percent improvement in the accuracy of foreign wheat
production forecasts could yield the United States as much as $200
million annually in benefits.
With Landsat it becomes possible to establish a global food
watch that could help humanity avoid disastrous food shortages. At
the World Food Conference in Rome in November, 1974, then United
States Secretary of State Henry Kissinger referred to the experiment
as a "... promising and potential vital contribution to rational
planning of global (food) production."
Landsat imagery of circulation and sedimentation patterns
along seacoasts has been used by Delaware to devise a strategy for
deploying equipment to contain oil spills, by Alaska to aid navigation
in Cook Inlet, by California to select recreational areas, and by
Japan to monitor pollution in Osaka Bay.
Information about faults and fracture zones derived from
Landsat imagery has been used in the United States and abroad to
select locations for new power plants, and determine the best routes
for oil and gas pipelines. in one case, Landsat data revealed a fault
across the proposed path of a new gas pipeline in Bolivia. Engineers
chose a different route that avoided the fault zone. The new path was
actually shorter than the original one, decreasing the cost of
building the pipeline - an unexpected but welcome benefit.
In the later 1970's a prolonged drought brought starvation
and death to millions of people in the Sahel, a vast African prairie
just south of the Sahara Desert. The desert has been creeping
steadily south for years, eliminating the marginal livelihood offered
by the dry prairie. At the request of a number of countries in the
area, Landsat surveyed the Sahel. One of the photographs dramatically
illustrated the problem. A polygonal-shaped patch of vegetation stood
out from the surrounding dry parched land. This was the area enclosed
from the fenced ranch, where careful management had prevented the
livestock from overgrazing and denuding the land. Despite the
dryness, the grass survived if not required to support too many
animals.
The lesson of the successful ranch, applicable to other
semiarid regions of the world, is that livestock management techniques
and control of the number of animals can preserve the grass cover,
preventing the encroachment of deserts or the formation of new
dustbowls.
Landsat pictures have helped Alaskan Indians select
thousands of acres of timberland and mineral exploration areas from
vast wilderness tracts offered by the federal government to settle
native claims going back to 1867, when the United States purchased
Alaska from Russia. Ninety-nine million acres were set aside for the
selection of 40 million acres of surface title and mineral rights by
about 210 villages and regional corporations, representing some
100,000 Indians, Eskimos, and Aleuts.
In remote Antarctica, Landsat cameras revealed previously
unknown groups of mountains in southern Victoria Land and at the head
of Lambert Glacier. They also disclosed significant changes in the
location of Burke Island, in the size and position of the Thwaites
Iceberg Tongue, and in long stretches of the Antarctic coastline.
Although water or ice covers three-quarters of the globe,
less than one-hundredth of one percent of this can be economically
extracted for a water supply. Landsat can help identify and monitor
these limited resources.
Landsat images can also indicate the accumulation of winter
snows in the mountains and help to estimate the springtime runoff of
water from melting snow. This water will later be available for
farming, hydroelectric power, and industrial and consumer use. A
single Landsat image can cover an entire region, such as the
Salt-Verde Watershed in the Arizona mountains. A mosaic of many
aerial photographs would have to be constructed to cover this
extensive, sprawling area.
While helping to monitor water quality in two Virginia
reservoirs, Landsat revealed small lakes that were not depicted on
Virginia maps. Landsat also keeps watch on water levels in a number
of Canadian reservoirs that serve hydroelectric power plants.
Landsat imagery is used to help government and private
organizations assess flood damage and plan disaster relief and flood
control programs. In 1975, for example, the governors of Arkansas,
Mississippi, and Louisiana requested rapid deliveries of Landsat
information showing the extent of flooding in their respective states
by the rampaging Mississippi River. They received the data in about
36 hours. It would have taken several days to collect the same
information by aerial photography. Pakistan and Australia have also
employed Landsat data to assess flood damage in their territories.
Landsat images clearly show ice types and the distribution,
growth, movement, and break-up of sea ice. This information grows in
importance as the resources of Alaska and the Arctic are developed.
Shippers can learn which ports are ice free, and can chart courses
through open waters in largely ice-covered seas. Canada has also used
Landsat images to route ships through its icy Arctic waters.
Perhaps one of the most dramatic illustrations of the
usefulness of Landsat data to ships operating in frozen polar seas
occurred in 1975, during the scientific expedition of the U.S. Coast
Guard icebreaker "Burton Island." The ship was guided through almost
solid pack ice in Antarctica's relatively unexplored Pine Island Bay,
following narrow channels of open water that were visible only in
Landsat photographs.
The Landsat program has demonstrated an ability to provide a
wide variety of highly useful information. Some other benefits
include using Landsat data as courtroom evidence in reaching agreement
on land development, to show how air pollution can affect weather, to
aid planning for control of forest fires that can plague California in
the summer, and to map forest fires in other countries.