Water: A Precious Resource in the Yanqi Basin. Editor’s Note: Today’s caption is the answer to Earth Observatory’s August satellite puzzler. The Yanqi Basin, in China’s Xinjian Province, lies in the Taklamakan Desert. The basin receives an average of just 80 mm (3 inches) of precipitation per year, making it one of the driest places in the world. An indication of this are the dunes visible in the top image, which was acquired on September 17, 2000, by the Enhanced Thematic Mapper Plus (ETM+) on Landsat 7.
Snow and glacial melt from the Tian Shan and Borohoro Mountains, which lie to the west, provide enough water to feed the Kaidu River (lower image). The Kaidu drains into Bositeng Lake, the largest body of fresh water in Xinjian. The shallow lake, 17 meters (58 feet) at its deepest point, used to be much saltier. West of the dam, there is a marshy area dense with reeds. The agricultural activity has not come without consequences. Instrument(s): Landsat 7 - ETM+ Sea Ice Retreats in the Northwest Passage. Ice retreated rapidly in the Parry Channel—part of the famous and elusive Northwest Passage—between mid-July and early August 2012.
These images, acquired by the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite, show significant changes over two weeks. The top image shows Parry Channel on July 17, 2012, when ice filled the channel. The bottom image shows the same region on August 3, when some ice was still clinging to the shores of Victoria and Melville Islands but open water otherwise dominated the region. The Canadian Ice Service reported that ice cover in Parry Channel began to fall below the 1981–2010 median after July 16, 2012, and the loss accelerated over the following two weeks. These photo-like images show widespread open water in early August, though patches of ice linger south of Melville Island. Whether or not ships can easily pass, recent studies have suggested that certain organisms have begun to take advantage of the open water. Terra - MODIS. Image of the Day.
Greatest Hits from Landsat : Feature Articles. Deforestation in the Amazon Rainforest takes on many different patterns. In Rondônia, a state in Western Brazil, deforestation took on the fishbone pattern revealed in these Landsat images from 1975 and 2012. Access to this remote region began with the building of a major road stretching from north to south. Secondary roads were then slowly cut through the dense forest at right angles to the initial road. Settlers cleared the area by first cutting and then burning the forest. As farmed lands grew larger and closer together, they began to merge into a large area of deforestation with a distinctive pattern. “Because these roads cut deep into the rainforest and then spread outwards, there’s a much greater loss of habitat and species than if there was a single area of deforestation because the amount of edge is critical for biodiversity,” said Compton Tucker, a biologist at NASA’s Goddard Space Flight Center.
First of Three Million. Forty years ago, after more than a decade working to leave our planet, NASA launched an unprecedented mission to look back at home. Four decades later, the Landsat program is still going strong, with more than three million images of Earth in its archives and a new mission slated for launch in 2013. On July 23, 1972, the Earth Resources Technology Satellite (later renamed Landsat 1) lifted off on a Thor-Delta (Delta 900) rocket from Vandenberg Air Force Base in California. The first images from the satellite’s Multispectral Scanner System (MSS) were received a day later by scientists gathered at NASA’s Goddard Space Flight Center in Maryland. The very first image in the Landsat archive is the MSS image above, showing the greater Dallas area of Texas on July 25, 1972.
Scientists involved in the mission weren't sure what to expect of the MSS, which used new fiber-optic technology, took pictures in four different bands of the spectrum, and scanned the Earth in strips. Instrument(s): Tahiti, French Polynesia. In August 1768, Captain James Cook, naturalist Joseph Banks, and a shipload of sailors set sail from England to Tahiti to observe the Transit of Venus. Camped out on Point Venus, they witnessed the event on June 3, 1769. Cook sketched the transit, but Banks had surprisingly little to say about it. Perhaps he was distracted by the wonders of the island itself. The Enhanced Thematic Mapper Plus on the Landsat 7 satellite captured this natural-color image of Tahiti on July 11, 2001. This island is part of a volcanic chain formed by the northwestward movement of the Pacific Plate over a fixed hotspot.
Although Tahiti-Nui now has a fairly symmetrical contour, it has an asymmetrical three-dimensional shape. Yet something else besides volcanic activity has shaped Tahiti: rain. Though the Transit of Venus was the stated objective of the British expedition, Banks was likely more interested in Tahiti’s plants. Complementing the rich life on land is marine life around Tahiti’s perimeter. World of Change: Columbia Glacier, Alaska : Feature Articles. The Columbia Glacier descends from an ice field 3,050 meters (10,000 feet) above sea level, down the flanks of the Chugach Mountains, and into a narrow inlet that leads into Prince William Sound in southeastern Alaska.
It is one of the most rapidly changing glaciers in the world. The Columbia is a large tidewater glacier, flowing directly into the sea. When British explorers first surveyed it in 1794, its nose—or terminus—extended south to the northern edge of Heather Island, a small island near the mouth of Columbia Bay. The glacier held that position until 1980, when it began a rapid retreat that continues today.
These false-color images, captured by Landsat satellites, show how the glacier and the surrounding landscape has changed since 1986. The images were collected by similar sensors—the Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+)—on three different Landsat satellites (4, 5, and 7). The retreat has also changed the way the glacier flows. Retreat of Alaska’s Columbia Glacier. The Columbia Glacier descends from an ice field 3,050 meters (10,000 feet) above sea level, down the flanks of the Chugach Mountains, and into a narrow inlet that leads into Prince William Sound in southeastern Alaska.
It is one of the most rapidly changing glaciers in the world. The Columbia is a large tidewater glacier, flowing directly into the sea. When British explorers first surveyed it in 1794, its nose—or terminus—extended south to the northern edge of Heather Island, a small island near the mouth of Columbia Bay. The glacier held that position until 1980, when it began a rapid retreat that continues today. These two false-color images, both captured by the Thematic Mapper (TM) instrument on Landsat 5, show the glacier and the surrounding landscape in 1986 and 2011. In 1986, the glacier's terminus was just a few kilometers north of Heather Island.
Like bulldozers, glaciers lift, carry, and deposit sediment, rock, and other debris from Earth’s surface. The Seafloor Focuses and Merges Tsunami Waves. Scientists have known for years that the shape of the seafloor plays a role in how tsunami waves build up as they approach the coastline. Underwater topography also determines why some areas get hit worse than others.
But in the wake of the Tohoku-oki tsunami, scientists now know that seafloor topography affects the strength and height of a tsunami even in the deep ocean and at great distances from the genesis of the wave. Scientists had suspected that underwater mountains and chasms, as well as islands, played a role in deflecting tsunami waves in some places and amplifying them up in others. But it was not until three satellites passed over such waves in March 2011 that they could confirm it. Researchers from NASA’ Jet Propulsion Laboratory (JPL) and the Ohio State University (OSU) used satellite altimeters to observe “merging tsunamis”—wave fronts that combine to form single waves at double the previous height. Instrument(s): The Dead Sea. The Dead Sea is so named because its high salinity discourages the growth of fish, plants, and other wildlife. This salt lake resides in a depression in the Earth's crust, where the continents of Africa and Asia are pulling away from each other.
It has pulled in visitors and industries for thousands of years. The Dead Sea is the lowest surface feature on Earth, sitting roughly 1,300 feet (400 meters) below sea level. On a hot, dry summer day, the water level can drop as much as one inch (two to three centimeters) because of evaporation. The false-color images above were captured by the Landsat 1, 4, and 7 satellites. All three images include a combination of near-infrared, red, and green wavelengths. The ancient Egyptians used salts from the Dead Sea for mummification, fertilizers, and potash (a potassium-based salt). The region is also famous for its historical and religious significance. NASA and the U.S. Instrument(s): Landsat 7. Effects of the Tohoku Tsunami on the Kitakami River. In March 2011, a magnitude 9.0 earthquake—the fourth largest recorded since 1900—triggered a powerful tsunami that pummeled the northeastern coast of Japan.
The earthquake occurred offshore, about 130 kilometers (80 miles) east of Sendai at 2:46 p.m. on March 11. Within 20 minutes, massive swells of water started to inundate the mainland. The tallest waves and most devastating flooding from the 2011 Tōhoku-oki tsunami occurred along the jagged coast of northern Honshu, a landscape dimpled with bays and coves known as ria coast.
The steep, narrow bays of ria coasts trap and focus incoming tsunami waves, creating destructive swells and currents that can push huge volumes of water far inland, particularly along river channels. That's exactly what happened in the days before the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), an instrument on NASA's Terra satellite, captured the middle image above (on March 14, 2011). Instrument(s): Closeup of Tsunami Damage, Rikuzentakata. Situated along the coast of northeastern Japan, the town of Rikuzentakata once had a seemingly peaceful seascape, including pine trees and white-sand beaches. But on March 11, 2011, a tsunami wave traveling up Hirota Bay reduced the town of 23,000 residents to rubble. This natural-color image from the WorldView-2 satellite shows Rikuzentakata three days later, on March 14. In the wake of the tsunami, several large buildings stood out from a landscape of debris.
Both the town and the nearby bay appear in shades of tan; farmland south of the town hall is inundated, while sediment colors the water off the coast. The mud in Hirota Bay was scraped from the richly vegetated barrier island that once stood between the town and the sea. (Other NASA satellite images show this area in 2011 and in 2007, when the barrier island was still intact.) More than two centuries ago, settlers planted more than 60,000 trees along the beach to protect inland fields from salt and sand. Instrument(s): Ice on the Dnieper River, Ukraine. Wreckage and Recovery in Ishinomaki, Japan. At the northern end of Sendai Bay, Ishinomaki once boasted one of the world’s largest fish markets.
On March 11, 2011, the earthquake and tsunami destroyed about 28,000 of the port city’s houses. More than 3,000 residents perished, and nearly three months later, almost as many people remained missing. These false-color images compare conditions in Ishinomaki immediately after the earthquake and tsunami, and then a year later. The top image, acquired by the Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite, shows Ishinomaki on February 21, 2012. The bottom image, acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite, shows the same area on March 14, 2011. In these false-color images, water is blue, vegetation is red, and bare ground and urban areas range from blue-gray to pink-beige.
The biggest difference between these images is the retreat of flood water. ReferencesCyranoski, D. (2012, March 8). Tiny Shrimp, Big Changes. Along the Pacific coast of Honduras and Nicaragua, in the Gulf of Fonseca, the landscape has changed over the past forty years. An aquaculture industry has developed, producing a bountiful harvest of shrimp within sight of coastal mangroves and wetlands. The shrimp farms also produce a rich harvest of arguments, with some people seeing an economic success story and a reasonable use of coastal land, while others decry unnecessary and destructive changes to wetlands. All three images above show the eastern end of the Gulf of Fonseca as viewed by the Thematic Mapper (TM) instrument on Landsat 5.
The top image was acquired on January 19, 1986; the middle on January 23, 1999; and the bottom image on January 8, 2011. In these natural-color images, tidal (salt) flats are shades of beige and gray, mangroves are dark green and edged in brown, and inland agricultural lands are shades of brown and light green. In the images, more ponds are dry in January 2011 than in January 1999. Instrument(s):
The Many Hues of London. The Enhanced Thematic Mapper Plus (ETM+), the sole instrument on the Landsat 7 satellite, is far more than a camera. While a typical point-and-shoot digital camera takes one picture of a scene based on information from the visible portion of the electromagnetic spectrum, the ETM+ generates eight separate views of everything it images. The ETM+ senses electromagnetic radiation in seven different bands, plus an additional panchromatic band that combines a broad range of wavelengths to create a high-resolution image.
Three of them (bands 1, 2, 3) are in the visible portion of the spectrum and correspond to blue, green, and red light. The other four bands (4, 5, 6, 7) fall in the infrared portion. Band 4 is near infrared, with a slightly longer wavelength than visible light. Combining the three visible bands produces a natural-color view, such as the top image of London. Further Reading NASA Landsat Education and Public Outreach Team (2006, June) How Landsat Images Are Made (pdf). Satellites Map Fine Aerosol Pollution Over China. Many types of aerosol particles circulate in the atmosphere, but one of the most damaging to human health is known as PM2.5, a technical term for microscopic bits of matter less than 2.5 microns in diameter (one thirtieth the width of a human hair). These small pollutants, which come mostly from burning fossil fuels and biomass, can lodge deep in the lungs, where they exacerbate a variety of respiratory and cardiovascular diseases.
Ground-based instruments are the standard for monitoring PM2.5 in many industrialized nations. For example, the U.S. Environmental Protection Agency, along with state and local governments, maintain a network of about 10,000 ground stations that generate real-time air quality measurements for hundreds of cities. However, not all countries have ground-based monitoring systems that measure such fine-grained pollutants. Satellites offer a perspective on PM2.5 that is particularly useful when ground instruments are unavailable or offer limited information. Deforestation in the Democratic Republic of the Congo.