Space Today Online - Terra - NASA's Earth Observing System satellite flagship

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Terra: Earth Observing System Flagship

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Click to enlarge this photo of our planet by the Earth Observing System flagship Terra. This spectacular "blue marble" was the most detailed true-color image of the entire Earth to date. Using a collection of satellite-based observations, scientists and visualizers stitched together months of observations of the land surface, oceans, sea ice and clouds into a seamless true-color mosaic of every square kilometer (.386 square mile) of our planet. More images for educators, scientists, museums and the public can be found at Goddard Space Flight Center's Earth Observatory page.

Terra is the flagship of NASA's Earth Observing System, a series of satellites gazing down on our planet from the unique vantage point of space.

Focused on measurements identified as important by U.S. and international scientists, Terra enables research into how Earth's lands, oceans, air, ice and life function together as an environmental system.

Earth has been changing constantly during its 4.5-billion-year history. Natural geological forces have been rearranging the surface features and climatic conditions of our planet since its beginning.

Today, there is scientific evidence that human activities have attained the magnitude of a geological force and are speeding up the rates of global changes. For example, carbon dioxide levels have risen 30 percent since the industrial revolution. About 40 percent of the world's land surface has been transformed by humans.

We don't understand the cause-and-effect relationships among Earth's lands, oceans and atmosphere well enough to predict the impacts rapid changes will have on future climate conditions.

About the Terra spacecraft:

Terra, formerly known as EOS AM-1, is the size of a small school bus. It carries a payload of five sensors that study interactions among Earth's atmosphere, lands, oceans, life and radiant energy (heat and light). Each sensor is designed to meet a wide range of science objectives. Two of the instruments were supplied by Canada and Japan.

Terra is in a 100-minute polar orbit 437 miles above Earth, flying in close formation with the photography satellite Landsat 7, which was launched in April 1999. Terra will be joined later by a complementary satellite, Aqua, formerly known as EOS PM-1, that will cross over the equator each orbit at a later time.

Click to enlarge NASA artisit's view of Terra, the Earth Observing System flagship, in orbit

Terra circles Earth from pole to pole in an orbit that descends across the equator at 10:30 a.m. when cloud cover is minimal and its view of the surface is least obstructed. The orbit is perpendicular to the direction of Earth's spin.

Swaths viewed from each overhead pass are compiled into whole-globe images. Over time, the global images enable scientists to show and tell stories of the causes and effects of global climate change. Terra eventually should allow meteorologists to create forecasts months, even seasons, ahead.

Terra sensors:

The sensors on Terra do not actively scan the surface like laser beams or microwave pulses might. Rather, they work like a camera. Sunlight reflected by Earth, and heat emitted by Earth, pass through the apertures of Terra's sensors. That radiant energy is focused on detectors that are sensitive to selected regions of the electromagnetic spectrum, ranging from visible light to heat.

The information produced by the detectors is transmitted down to Earth and processed by computers into images that people can interpret. Terra will send down as much as one terabyte of data a day.

Terra's instruments monitor Earth's radiation balance, including the effect of heavier cloud cover on the amounts of solar radiation absorbed by the planet. Sea surface temperatures and levels of greenhouse gases are gauged. They also measure changes in land cover use, including those attributable to human activity; ice sheet volume; chemistry of the mid to upper atmosphere; and the effects of volcanic activity on the atmosphere.

Terra's life expectancy is 6 years. It and Aqua will be followed in space by other EOS satellites using later remote sensing technology. EOS will continue to build the climate database for fifteen to eighteen years.

NASA TV shows the launch of Terra on December 18, 1999, from Vandenberg Air Force Base, California, aboard an Atlas 2-AS rocket.

What we want to know:

As we learn more about our home planet, new questions draw us deeper into thecomplexities of Earth's climate. There are many important questions for which we don't have answers:

Is the current warming trend temporary or the start of a permanent increase in global temperatures?

How will rising temperatures affect weather, food production and sea level?

Are the number and sizes of clouds increasing? How will they affect the amount of incoming and reflected sunlight, as well as the heat emitted from Earth's surface?

What are the causes and affects of ozone fluctuations?

How will climate change affect health, natural resources and economies?
Terra and EOS will help researchers answer these questions, and probably some we haven't thought of today.

Click to enlarge NASA's EOS logo

Earth Observing System:

Scientists need to take measurements all over the world, over a long period of time, to be able to assemble the information needed to construct accurate computer models that will enable them to forecast the causes and effects of climate change.

At this time, the only feasible way to collect such widespread information is through the use of so-called remote sensors in space. That is, satellites orbiting Earth and carrying instruments that can measure things like temperature from a distance. Terra, Aqua and Aura are such satellites.

NASA built its Earth Observing System (EOS) as an international study of planet Earth. EOS has three main parts:

a series of satellites designed to study the complexities of global change

an advanced computer network called EOSDIS for processing, storing and distributing data

teams of scientists around the globe studying the data
EOS Direct Broadcast:

The EOS satellites broadcasts data for reception by anyone around the world.

Aqua broadcasts data from its science instruments AIRS/AMSU-A/HSB, AMSR-E, CERES, and MODIS on X-Band radio. The satellite broadcasts continuously except for five-minute interruptions once per obit when it contacts its ground stations at Poker Flat, Alaska, and Svalbard, Norway.

Terra broadcasts portions of the data from its MODIS science instrument on X-Band. The broadcast is continuous except when the satellite is dumping its play-back data to ground stations for 15 minutes each orbit, and when Terra is within line-of-sight of NASA Deep Space Network (DSN) stations at Goldstone, California, Canberra, Australia, and Madrid, Spain.

Anyone interested in obtaining direct broadcast data or establishing a downlink site should navigate to the EOS Direct Broadcast Web site.
[ EOS Direct Broadcast Web site »» ]

Earth Science Enterprise:

NASA has positioned EOS as the centerpiece of what it calls an Earth Science Enterprise (ESE). In the U.S. space agency's words, EOS is a scientific information gathering system and a data storage and retrieval system supporting a coordinated series of polar-orbiting and low inclination satellites for long-term global observations of the land surface, biosphere, solid Earth, atmosphere and oceans.