They’re up there now, scanning the planet at all wavelengths, taking the measure of its shifting seas, winds, and landforms. Earth-viewing satellites have been around for 40 years, but none like these. A new generation of remote sensing spacecraft has brought unprecedented clarity and coverage to the study of Earth from space, and we now live on a continuously monitored planet.
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In the 1980s NASA conceived of a grand “Mission to Planet Earth”—a fleet of large satellite platforms, each carrying a suite of sensors that together would provide a long-term record of environmental change. It didn’t turn out that way, mostly due to the multibillion-dollar cost. But a less expensive Earth Observing System (EOS) is reaching orbit, with the first major component launched in 1999.
Terra, as it’s called, retains the original concept’s Swiss army knife approach to Earth observation. Each of the five onboard sensors has its own specialty. A versatile spectrometer called MODIS takes regional-scale pictures in 36 wavelengths. The multi-angle MISR has nine separate cameras—four pointing forward, one straight down, and four looking backward—so that hard-to-see phenomena like atmospheric haze can be photographed in different angles of illumination. ASTER, the one Japanese instrument on board, is Terra’s zoom lens; its high resolution is suitable for a range of tasks, from studying glaciers to tracking changes in land use. MOPITT is tuned to the infrared signatures of pollutants in the lower atmosphere, and CERES measures global radiation to help answer the critical question of what role clouds play in global warming or cooling.
Documenting global change is in fact the main quest of Terra and the rest of the new satellite sensors. They watch for signs that coral reefs are dying, that snowpacks are melting, that forests are disappearing, or shorelines are shifting. More importantly, they collect fundamental data—trillions of bytes’ worth—revealing the complex interplay of land, air, ice, and water driving our planet’s weather.
Terra will be followed later this year by the second large EOS platform, Aqua, which will focus on the atmosphere and ocean. By the end of 2003, some two dozen EOS satellites of varying size and scope will be in space. Add the data from non-EOS projects, like the Shuttle Radar Topography Mission, which last year mapped 80 percent of Earth’s surface in 3-D, and Earth scientists are happily swamped with information. “These days there’s so much data around that you can’t possibly look at it all,” says Alexander Goetz, who heads the University of Colorado’s Center for the Study of Earth from Space.
More is on the way. With the launch of the EO-1 (Earth Observing 1) technology-testing satellite in November, NASA has made its first foray into space-based hyperspectral imagery, which sees in more than 200 wavelengths instead of the few bands covered by older satellites like Landsat, and lets scientists better characterize surface materials based on the way they reflect or absorb light. The first commercial space images with one-meter resolution have already hit the market, with more sharp-eyed competitors on the way.
For students of planet Earth, the view is getting better all the time.
Browse images in the Photo Gallery at right.