NASA: Pacific Ocean - Steam Plume at Gaua Volcano - Australia coast - A Better Eye on Reefs - 07.07.13

Posted by ricardo marcenaro | Posted in | Posted on 17:46

Steam Plume at Gaua Volcano
acquired May 31, 2013 download large image (2 MB, JPEG, 3824x2549)
Just 20 kilometers (12 miles) in diameter, Gaua Island is actually the exposed upper cone and summit of a stratovolcano that is 3,000 meters (10,000 feet) high and 40 kilometers (25 miles) in diameter. Most of the volcano is submerged beneath the Pacific Ocean. Also known as Santa Maria Island, Gaua is part of the Vanuatu Archipelago, a group of volcanic islands in the South Pacific Ocean governed by the Republic of Vanuatu.
According to the Smithsonian Institution Global Volcanism Program, the most recent report of eruption activity at Gaua was a steam plume observed on April 29, 2013. This photograph records subsequent steam emissions observed on May 31, 2013, by an astronaut on the International Space Station. The steam plume extends east-southeast from its likely source at Mount Gharat (also spelled Garat or Garet), a historically active cinder cone located along the southwest flank of a 6 by 9 kilometer (4 by 6 mile) collapsed summit caldera. Gaua is one of several volcanoes monitored by the Vanuatu Geohazards Observatory.
The dark blue-green waters of Lake Letas, formed within the caldera, are visible at image center. The majority of Santa Maria Island is covered in green vegetation, with areas directly west and south of Mount Gharat covered with grey ash deposits. Patchy cloud cover is visible to the west and south, but is easily distinguished from the steam plume by its linear nature and brighter tone.
Astronaut photograph ISS036-E-5647 was acquired on May 31, 2013, with a Nikon D3S digital camera using a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Laboratory, Johnson Space Center. The image was taken by the Expedition 36 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by William L. Stefanov, Jacobs/JETS at NASA-JSC.
ISS - Digital Camera

A Better Eye on Reefs

A Better Eye on Reefs
acquired April 20, 2013 download large image (4 MB, JPEG, 4000x3000)
acquired April 20, 2013 download GeoTIFF file (20 MB, TIFF)
The concept behind Landsat is to gather images of Earth’s land surfaces. But in four decades of service to science, the satellites have proven to themselves quite useful for observing some blue parts of the planet, too.
The study of coral reefs has been particularly enriched by Landsat. Scientists used earlier generations of Landsats to create a global image library of coral reefs. They have also been able to do time-series assessments of the health of some reefs. For instance, researchers used 18 years of Landsat data to show a decline in the health of reef habitat across roughly 68 percent of the Florida Keys National Marine Sanctuary. Satellite images also can detect signs of trawling and other fishing activities that can be harmful to reefs.
“The remote location and massive size of reefs make them an ideal subject for Landsat remote sensing,” said Phillip Dustan, a marine biologist at the College of Charleston (South Carolina) who has worked with Landsat to map reefs around the world. “Reef management benefits from satellite imagery through mapping, change analysis, and threat assessment, While a single image can be used to provide mapping data, the long-term data set provided by Landsat makes for powerful time series of images that can probe the dynamics of ecological change.”
This image of Princess Charlotte Bay in Australia was acquired by the Operational Land Imager (OLI) on Landsat 8 on April 20, 2013, while the satellite was still being calibrated and checked out. The area lies along the east coast of Queensland’s Cape York Peninsula. The scene shows Claremont Isles National Park, where coastal waters are protected as part of Great Barrier Reef World Heritage Site. The islands are important habitat and breeding grounds for seabirds, and they are off-limits to humans.
“Coral reefs continue to change rapidly in response to stresses applied at scales from local to global,” Dustan added. “The very adaptations that make corals so successful in nutrient-poor, clear tropical waters also leave them vulnerable to climate- and ocean chemistry change.”
Landsat 8 has better spatial resolution and greater sensitivity to brightness and color, known as dynamic range. The OLI image above uses a combination of red, green, and shortwave blue light—a special band of wavelengths (0.43–0.45 micrometers) that scientists call “coastal blue”—to better distinguish features in coastal waters.
Near the coast, weather patterns, natural aerosols, air pollutants, waves and currents, and floating material can distort, reflect, and refract light signals. The coastal blue band can be compared with other wavelengths to remove this environmental “noise” and better tease out fine structures. The blue band is also similar to wavelengths observed by previous NASA satellite sensors, so Landsat 8 allows researchers to extend scientific records that go back decades.
Earth Observatory images by Jesse Allen and Robert Simmon, using data provided by the U.S. Geological Survey. Caption by Michael Carlowicz.
Landsat 8 - OLI

NASA: Pacific Ocean - Steam Plume at Gaua Volcano - Australia coast - A Better Eye on Reefs - 07.07.13

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