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The View From Above

Satellite imagery is giving biologists a whole new perspective on the phenomena they study.

By | February 1, 2012

The Millennium Coral Reef Mapping project created the first ever map of coral reefs around the world using more than 1,000 coastal images obtained from the Landsat 7 satellite, such as this coral reef system in Los Roques, Venezuela. NASA/USGS

The Millennium Coral Reef Mapping project created the first ever map of coral reefs around the world using more than 1,000 coastal images obtained from the Landsat 7 satellite, such as this coral reef system in Los Roques, Venezuela. NASA/USGS

The Millennium Coral Reef Mapping project created the first ever map of coral reefs around the world using more than 1,000 coastal images obtained from the Landsat 7 satellite, such as this coral reef system in Los Roques, Venezuela. NASA/USGS
Landsat 7 image of coral reef in Male, Maldives. Red areas denote photosynthetic vegetation.Courtesy of Frank Muller-Karger
Landsat 7 image of coral reef in Takebone, Indonesia. Red areas denote photosynthetic vegetation.Courtesy of Frank Muller-Karger
For a couple of days in January 2010, the waters off the Florida coast plunged to a record-low 11°C—well below the 15°C temperature threshold at which corals begin to bleach. The blue areas in the map corresponds to anomalously cold sea surface temperatures in the coastal waters of Florida during January 2010. This was enough to cause a massive die-off of corals near the Florida shore. Of the two bleached corals from Florida pictured above, the top still has a few areas of pigmentation due to the presence of algal endosymbionts, while the coral on the bottom is completely bleached. Fluctuations in water temperature that lead to thermal stress in corals are being monitored on a daily basis by NOAA’s Coral Reef Watch Satellite Bleaching Alert system, which is based on daily sea-surface temperature satellite measurements. Diego Lirman (corals), Frank Muller-Karger (map)
Marine biologist at the University of Technology in Sydney, Elizabeth Madin, uses Google Earth to study grazing halos—rings of bare sand surrounding coral reefs formed by tiny herbivores grazing close to the reef—which are readily visible in this image of a Red Sea coral reef.Google Earth on January 10, 2011, Copyright 2011 Europa Technologies, Tele Atlas, Digitalglobe
Marine biologist Elizabeth Madin first got the idea of using Google Earth to look at grazing halos while on a field trip to Australia's Heron Island pictured here.Google Earth on January 10, 2011, Copyright 2011 Europa Technologies, Tele Atlas, Digitalglobe
In the 1960s, microbiologist Rita Colwell proposed that Vibrio cholerae was a marine bacterium that lives in association with zooplankton. Many decades later, Colwell uses satellite measurements of chlorophyll concentrations in the oceans to track and predict cholera outbreaks. Chlorophyll serves as a proxy for phytoplankton blooms, which are food for the cholera-laden zooplankton. This image shows a seven-year average of phytoplankton chlorophyll concentration in the world's oceansNASA's Goddard Space Flight Center
Scientists at NASA are using satellite measurements of sea-surface temperatures and land vegetation greening to predict outbreaks of Rift Valley fever in East Africa. This map shows anomalies in sea-surface temperatures and in the Normalized Difference Vegetation Index (NDVI), which quantifies the amount of vegetation cover (based on visible and near-infrared reflectance data from sensors onboard NOAA’s polar orbiting satellites), observed globally in January 2007. The unusually high sea surface temperatures (teal) sustained in the western equatorial Indian Ocean and the central and eastern equatorial Pacific Ocean since the summer of 2006 had caused an anomalous growth in vegetation (purple), in Eastern Africa due to heavy rainfall. This in turn led to a population boom of mosquitoes carrying Rift Valley fever virus.NASA/Goddard Space Flight Center Scientific Visualization Studio
Areas in East Africa that experienced unusual greening of vegetation (shown in the image on top in green) in December 2006, corresponded to areas under increased risk of a Rift Valley fever outbreak (shown in the image on the bottom as red). Indeed the yellow dots show human Rift Valley fever cases that occurred inside the predicted risk areas.NASA's Goddard Space Flight Center
Satellite measurements of artificial light intensity at night have been used in a variety of fields including ecology and epidemiology. For example, a team led by evolutionary biologist at Princeton University Nita Bharti recently used satellite imagery to track changes in concentration of nighttime light in Niger as a proxy for migrations of human populations into and out of cities. The researchers are currently using that data to get a better understanding of the environmental patterns underlying measles outbreaks.NASA
In 2001, researchers working for the US Army fenced off a lava-surrounded patch of forest, or kipuka, known as Alala (shown above), in order to save the native fauna and flora from the destructive grazing of goats. In order to get a better sense of whether the removal of goats had enabled the regrowth of native flora, researchers led by James Kellner from the University of Maryland turned to satellite imagery. to NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS)—an instrument aboard the Terra and Aqua satellites that has been measuring the visible and near-infrared light reflected from the Earth’s surface since the satellites were launched into space in 1999 and 2002. Using a data set encompassing nine years, the team was able to quantify how the vegetation cover had changed over time.Google Earth on January 10, 2012, Copyright 2011 Europa Technologies, Tele Atlas, Digitalglobe
By removing the goats from kipuka alala, Hawaiian authorities hoped to protect the critically endangered Palila honeycreeper bird, which nests and feeds mainly on the seeds of the mamane tree (far right), also endangered. Satellite, airborne, and on-the-ground analysis of vegetation density and composition in Kipuka Alala suggests that the removal of goats seems to have had the unintended effect of enabling the expansion of invasive weed species such as fountain grass and fireweed (weed with flowers). Both are of major concern because fountain grass increases the risk of intense wildfires, and fireweed is toxic to livestock.Ryan P. O'Donnell (bird); Jim Kellner (fireweed)

The View From Above Image Gallery

The Millennium Coral Reef Mapping project created the first ever map of coral reefs around the world using more than 1,000 coastal images obtained from the Landsat 7 satellite, such as this coral reef system in Los Roques, Venezuela. NASA/USGS

Life scientists from a wide range of fields—from ecology and epidemiology to anthropology, marine microbiology, and animal behavior—are increasingly turning to rapidly advancing and ever-more-accessible satellite imagery to gain a more sophisticated, big-picture understanding of how organisms interact not only with their immediate environments, but also with the more expansive, global landscape.

Read the full story.
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Tags

satellites, remote-sensing, Landsat, infectious disease, Google Earth, ecology, coral reefs and biodiversity
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