Figure 1 SeaWiFS data over the Pacific Ocean, including a 32-day average from September 22, 2006 to October 23, 2006. Dark blue represents warmer areas where there is little plant life due to lack of nutrients, and greens and reds represent cooler nutrient-rich areas with more abundant plant life.

Zooming in on Climate Change

Dan Stillman
Science Communications Specialist
Institute for Global Environmental
Strategies
Arlington, Va.
www.strategies.org

Thanks to the routine display of cloud cover during TV weather forecasts and the incorporation of satellite imagery into mapping platforms, including Google Earth and Microsoft Virtual Earth, the value of satellite technology has never been more apparent. However, such applications do not come close to demonstrating the full potential of satellites to serve society, especially those of high-resolution commercial satellites in the increasingly important area of climate change.

Two recent reports by the Intergovernmental Panel on Climate Change have elevated the urgency of climate change research. The panel said in February 2007 that “warming of the climate system is unequivocal,” and then in April warned that “many natural systems are being affected by regional climate changes, particularly temperature increases.”

Citing cost concerns and a need to view broad geographic areas, scientists have traditionally gravitated toward publicly available, lower-resolution satellite imagery for the purposes of studying climate change signals and impacts. But Mark Brender, vice president of marketing and corporate communications at GeoEye (Dulles, Va.), a major producer of satellite, aerial and geospatial information, says that evolving technology is turning up a growing number of uses for commercial imagery in climate-related research.

Figure 2 This four-meter IKONOS satellite image of Baker Island, located approximately 1,650 miles southwest of Honolulu, Hawaii, is being used by NOAA to monitor the coral reef ecosystem surrounding the island. Baker Island is about 1.6 square kilometers in size with the highest elevation of only 20 feet above sea level, and is a national wildlife refuge under the authority of the U.S. Fish and Wildlife Service. NOAA research has shown that IKONOS imagery has been found to have a depth penetration of up to 30 meters in clear water. Visible on the island is an abandoned airstrip.

Baker Island is a national wildlife refuge, with sparsely scattered vegetation and no trees. It is not within the jurisdiction of any specific state of the U.S. Administrative authority was transferred from the Office of Territorial Affairs to U.S. Fish and Wildlife Service in 1974. The island has remained unoccupied since 1942 when it was attacked by the Japanese during World War II. At this time, public use is restricted to scientists and educators by special permit. IKONOS satellite image courtesy of GeoEye.

“The commercial remote sensing industry is an extra set of eyes in the sky that can be utilized in looking at a host of climate change indicators, including glaciers and coral reefs, and in the verification and monitoring of carbon sequestration efforts,” Brender said. “While high-resolution imaging satellites can't see climate change, they can certainly see the impact climate change has over the long term.”

That sentiment is echoed by Chuck Herring, director of corporate communications at DigitalGlobe (Longmont, Colo.), also a major provider of commercial satellite imagery and geospatial information. The resolution, accuracy and coverage of high-resolution commercial satellite imagery “makes it a perfect fit for documenting changes in the Earth for many different applications, from coastal monitoring to glacier melting to wildlife habitat mapping,” Herring said. Spot Image (Toulouse, France) also supplies imagery for a variety of climate change applications.

OBSERVING OCEANS

One discipline already benefiting from commercial satellites is the monitoring of oceans. The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) on the OrbView-2 satellite, owned by GeoEye, has led to a better understanding of the ocean's role in the carbon cycle.

Figure 3  Buck Island Reef National Monument is located 1.5 miles off the northeast side of the island of St. Croix in the U.S. Virgin Islands. This image clearly shows an extensive underwater coral reef ecosystem. The reef is being studied and monitored by NOAA. Six thousand feet long and a half-mile wide, uninhabited Buck Island rises to 340 feet above sea level. The 880-acre National Monument includes 176 acres of land and 704 acres of water and coral reef system.

First protected in 1948, the area was proclaimed a national monument in 1961. Many endangered species nest on the island, including the brown pelican, hawksbill, leatherback and green sea turtles. Buck Island is not volcanic in origin: its sedimentary rocks were uplifted by tectonic pressures. Two thirds of this largely tropical dry forest island are surrounded by an Elkhorn coral reef, which includes the Marine Garden area, closed to fishing and collecting activities. Resembling haystacks, Elkhorn coral patch reefs are scattered along the outside of the forereef and rise nearly to the water's surface from the seabed as much as 40 feet below. IKONOS satellite image courtesy of GeoEye.

By comparing climate records with SeaWiFS measurements of ocean plant life, as indicated by ocean color, NASA scientists found that as Earth's climate warms, ocean plant life is decreased. This reduction in ocean plant life has negative impacts not only on fisheries and ecosystems, but also on the ocean's capacity to store carbon dioxide from the atmosphere, thus potentially producing a feedback effect of further warming. See Figure 1.

“SeaWiFS has been instrumental in increasing our understanding of the ocean's role in the carbon cycle, which affects what happens to all the carbon dioxide emitted by human activity,” said Greg Hammann, a senior director and chief oceanographer at GeoEye.

Figure 4 Pearl and Hermes Atoll, Northwestern Hawaiian Islands. The islands and atolls in the Hawaiian Archipelago are moving west at a rate of approximately 9 centimeters a year from the geologic “hotspot” from which all were formed. IKONOS image courtesy of GeoEye.

One of the ocean's most precious victims of warming may be coral reefs. A vital natural resource, coral reefs provide a safe habitat for about one million species of fish, act as a natural barrier in protecting tropical coasts from high waves and storm surges, and generate billions of dollars per year for local economies through recreational and commercial fishing. Warmer waters can lead to coral bleaching—the whitening of coral reefs due to the loss of microscopic algae—and the eventual death of coral. See Figures 2-6.

Measurements of sea-surface temperatures by the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer (NOAA's AVHRR), onboard its polar-orbiting satellites, are used to identify areas at risk for coral bleaching. High-resolution commercial satellites, like GeoEye's IKONOS and DigitalGlobe's QuickBird, can then penetrate 30 to 40 meters deep in clear water to detect features on the seafloor as small as a few meters in size. NOAA scientists are using data from these instruments to map every shallow-water coral reef within U.S. waters.

Tim Battista, a biological oceanographer for NOAA's Center for Coastal Monitoring and Assessment, explains that, for this purpose, satellite imagery is less expensive than airborne methods.

“A satellite allows us the flexibility to repeatedly shoot an area until we get an optimal scene, whereas the alternative is that you put an airborne platform over there, and you're kind of dictated on where you go based on where the clouds are on a given day, or the sea state,” Battista said. “It's much more cost-effective for us to shoot with a commercial satellite and wait the additional time for a good collection, than to put a plane on the ground somewhere with a limited time window.”

Figure 5 Kure Atoll in the Northwest Hawaiian Islands is located approximately 2,200 km west-northwest of Honolulu, and is the oldest emergent land area in the Hawaiian archipelago (approximately 30 million years). IKONOS image courtesy of GeoEye.

In the future, Battista expects commercial satellites to help coastal managers regularly monitor the distribution and health of coral reefs and their ecosystems, including the progress of reef restoration projects. “In order to do that, we have to have the imagery and methodologies that are cost-effective and efficient, and the commercial satellite imagery certainly plays a big part in that,” he said.

Commercial imagery has a role to play along the coast as well. In its effort to map shoreline change, NOAA augments medium-resolution data from Landsat with images from IKONOS and QuickBird.

“When you get down to right along the coast, the Landsat data fall apart—they're too coarse,” said Nicholas Schmidt, chief of NOAA's Coastal Geospatial Services. “When we start noticing trends or rapid development in certain areas, our plan is to use the high-resolution imagery to concentrate on those areas of high change.”

IMAGING ICE

Even more than coral reefs and shorelines, ice can provide some of the most telling and dramatic signs of climate change. In this area, too, commercial satellites are proving to be an important monitoring and mapping tool.

A recent study by scientists at Texas A&M University used 1-meter IKONOS imagery to measure the retreat of tropical glaciers on New Guinea's Mount Jaya. The researchers found that from 2000 to 2002, the total area covered by ice on the mountain decreased by 7.5 percent, continuing a trend that began in the mid-1800s.

The increasingly small size of these glaciers makes high-resolution imagery all the more critical. According to Texas A&M researcher Joni Kincaid, in 2000 the largest of the Mount Jaya glaciers occupied an area slightly larger than one square kilometer. With IKONOS, Kincaid was able to measure glacial changes to within one square meter, whereas lower-resolution imagery may not have captured changes on such a small scale.

“There are thousands of tropical glaciers. Unlike large glaciers, these small glaciers respond quickly to climate changes, and therefore it's important to be able to determine change over small time periods,” Kincaid said.

While Kincaid concentrates on tropical land ice, Burcu Cicek is focused on Antarctic sea ice. Late last year, the University of Texas, San Antonio researcher sailed with an international team of scientists on a Swedish icebreaker as it chiseled a channel through frozen McMurdo Sound, clearing the way for supply and fuel ships to reach McMurdo Station. Using IKONOS imagery, Cicek now plans to map the channel's length, its width, and the amount of ice inside it.

Figure 6 This image of the French Frigate Shoals in the Northwest Hawaiian Islands covers approximately 690 square km. IKONOS image courtesy of GeoEye.

IKONOS will also aid Cicek in the mapping and detection of change in Antarctic melt ponds, areas of water that form as snow melts on top of ice. As these ponds absorb more sunlight than surrounding ice, they gradually grow in area and depth. The resulting imbalance between absorbed and reflected energy can impact regional and global climate. Therefore, knowing when and where melt ponds form could lead to improved climate projections.

“High resolution means more detail,” Cicek said. “We especially need better resolution for the remote areas such as Antarctica, since we have limited access to the region.”

Melting ice is more than just a signal of a warming climate—it can disrupt wildlife and entire ecosystems. For example, melting sea ice is stranding Pacific walrus in the Arctic Ocean, threatening the stability of a species that native Alaskans rely on for food, clothing and shelter. Biologists with the U.S. Fish and Wildlife Service have been testing the usefulness of IKONOS and QuickBird to assist them in reliably estimating walrus counts.

Satellite imagery has long been a valuable tool for monitoring general characteristics, such as sea surface temperatures and water circulation, of marine mammal habitats. Now, with the advance of commercial high-resolution satellites, detailed population information can be collected in remote areas that are otherwise difficult to access.

“Earlier-generation satellites with lower spatial resolution were useful for imaging habitat features,” said Douglas Burn, a biologist at the U.S. Fish and Wildlife Service. “The advantage of high-resolution satellite imagery is that it allows us to image the animals themselves.”

CAPTURING CARBON

The capacity of high-resolution satellites to collect detailed, small-scale information may also play an important role as Europe and many U.S. states work to limit and reduce carbon emissions through carbon-trading programs. Some of these programs allow carbon emitters to gain carbon “credits” by paying farmers to maintain their land in a way that stores more carbon in soil, trees and grass, instead of releasing it to the atmosphere.

William Pickles, a physicist at the Lawrence Livermore National Laboratory, has tested the ability of airborne hyperspectral imagery to detect increases in soil carbon dioxide levels by observing resulting changes in plant life, and he says there's the potential to do the same from satellites. “Suppose you had a thousand sites over the whole world where CO2 was being sequestered, and you had a satellite that could measure one part per million CO2 and it could revisit all these sites every week or two.”

Another way carbon producers can earn credits is by agreeing to plant a certain amount of trees to store enough carbon to make up for that which they emit. Here again, Brender suggests, high-resolution commercial satellites may help to zoom in on specific locations to monitor and verify that trees were planted, and not subsequently damaged or lost.

“If, for example, a big oil company plants 1,000 trees in Laos in exchange for being able to build a plant in South Korea, who verifies the trees were planted, and not logged or destroyed by a storm?” Brender said. “High-resolution satellites are an ideal tool for verification and monitoring.”

As for cost, a factor that many government and university scientists say deters them from using commercial imagery, Brender says that it's not as expensive as some might think at $7.70/square km (minimum order of 49 square km). He also mentions the recently announced GeoEye Foundation, which awards imagery to university students and faculty, and to nongovernmental organizations, to advance research in GIS, environmental studies and humanitarian efforts.

“In the grand scheme of things, given the seriousness and impact of climate change, commercial satellite imagery should be considered another tool in the tool kit to help us better understand how changes in climate impact the environment,” Brender said.

Such tools are expected to become even more powerful with the next generation of commercial satellites scheduled to launch this year. GeoEye's GeoEye-1 and DigitalGlobe's WorldView I will boast resolutions of a half-meter or better, enabling even more detailed observations to support studies of Earth's changing climate.

 
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