Mount Everest Avalanche Location

On Friday, April 26, an avalanche on Mount Everest killed at least 13 Sherpa guides. The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft captured this perspective view image of the mountain and avalanche location on April 28, 2014. The avalanche occurred in an area nicknamed the "popcorn field" (red star), which is surrounded by ice boulders along the route leading through the Khumbu Icefall. This perspective view looks toward the northeast, with Everest in the center of the view, and Lhotse, the fourth-highest mountain on Earth, on the skyline to the right center.

Image credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

Karst Landscape in Guangxi Province, China

Karst topography is a geological formation shaped by the dissolution of layers of soluble rock such as limestone. Mature karst landscapes, where more bedrock has been removed than remains, may result in karst towers, or haystack/eggbox landscapes. Beneath the surface, complex underground drainage systems (such as karst aquifers) and extensive caves and cavern systems may form. A good example is found in Guangxi Province in southeast China. The image was acquired December 3, 2013, covers an area of 28 by 31.5 km, and is located at 24 degrees north, 107.9 degrees east.

Image credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

The Netherlands

This image over the west coast of the Netherlands is one of the early radar scans by the Sentinel-1A satellite, which was launched on 3 April.

The satellite’s advanced radar can provide imagery under all weather conditions and regardless of whether it is day or night. It can scan Earth’s surface in a range of different modes, enabling it to monitor large areas in lower resolution or to zoom in on a smaller region for a sharper view.

One of the many application areas of the data will be the surveillance of the marine environment, including monitoring oil spills and detecting ships for maritime security, as well as measuring wave height.

In this image, we can clearly see radar reflections from the ships at sea, appearing like stars in a night sky. The two collections of ‘stars’ are reflections from large-scale offshore wind farms, used to generate electricity.

Other visible features include the city of Amsterdam on the center-right side of the image, and the runways of the nearby Schiphol airport. In the lower part of the image we can see the city of Rotterdam, with Europe’s largest port extending to the left.

Sentinel-1’s radar will also be used for monitoring changes in agricultural land cover – important information for areas with intensive agriculture like the Netherlands.

This image, also featured on the Earth from Space video program, was acquired on 15 April with the radar operating in ‘stripmap mode’, which provides coverage at a resolution of about 10 m.

Sentinel-1A is the first in a fleet of satellites being developed for Europe’s Copernicus environmental monitoring program. The satellite is not yet in its operational orbit, but early images like this have given us a taste of what’s to come.

Image credit: ESA

Drought in the Congo Rain Forest

A view of the entire African rainforest area (green) transitions into a view of the region included in the Nature study, primarily in the Congo forest (mostly brown). The study area represents intact areas in the Congo rainforest where satellite data are high quality.

A new analysis of NASA satellite data shows Africa's Congo rainforest, the second-largest tropical rainforest in the world, has undergone a large-scale decline in greenness over the past decade.

The study, led by Liming Zhou of University at Albany, State University of New York, shows between 2000 and 2012, the decline affected an increasing amount of forest area and intensified. The research, published Wednesday in Nature, is one of the most comprehensive observational studies to explore the effects of long-term drought on the Congo rainforest using several independent satellite sensors.

"It's important to understand these changes because most climate models predict tropical forests may be under stress due to increasing severe water shortages in a warmer and drier 21st century climate," Zhou said.

Scientists use the satellite-derived "greenness" of forest regions as one indicator of a forest's health. While this study looks specifically at the impact of a persistent drought in the Congo region since 2000, researchers say that a continued drying trend might alter the composition and structure of the Congo rainforest, affecting its biodiversity and carbon storage.

Previous research used satellite-based measurements of vegetation greenness to investigate changes in the Amazon rainforest, notably the effects of severe short-term droughts in 2005 and 2010. Until now, little attention has been paid to African rainforests, where ground measurements are even sparser than in the Amazon and where droughts are less severe but last longer.

To clarify the impact of long-term drought on the Congo rainforest, Zhou and colleagues set out to see whether they could detect a trend in a satellite measure of vegetation greenness called the Enhanced Vegetation Index. This measure is developed from data produced by the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on NASA's Terra satellite. The scientists focused their analysis on intact, forested regions in the Congo Basin during the months of April, May and June each year - the first of the area's two peak rainy and growing seasons each year.

The study found a gradually decreasing trend in Congo rainforest greenness. The decrease, sometimes referred to as "browning," suggests a slow adjustment to the long-term drying trend. This is in contrast to the more immediate response seen in the Amazon, such as large-scale tree mortality, brought about by more episodic drought events.

The browning of the forest canopy is consistent with observed decreases in the amount of water available to plants, whether that is in the form of rainfall, water stored in the ground, water in near-surface soils, or water within the vegetation.

These changes in available water were detected in part with NASA satellites including the NASA/JAXA Tropical Rainfall Measuring Mission, NASA's Quick Scatterometer (QuikScat), and NASA's Gravity Recovery and Climate Experiment, a joint mission with the German Aerospace Center. The latter two missions are managed by NASA's Jet Propulsion Laboratory, Pasadena, California.

"Combining measurements from different sensors has given us more confidence in the results of the MODIS data and provided us with insights into the environmental and physiological mechanisms of the browning observed by the MODIS data," said co-author Sassan Saatchi of JPL.

Climate factors known to affect vegetation growth were also in line with the observed browning. Land surface temperatures, for example, were observed to increase over most of the study area. Decreased cloudiness allowed more solar radiation to reach the plants, which typically promotes photosynthesis, but in this case it likely posed an extra stress on the plants from the resulting depletion of soil moisture.

"Forests of the Congo Basin are known to be resilient to moderate climate change because they have been exposed to dry conditions in the past few hundred years," Saatchi said. "However, the recent climate anomalies as a result of climate change and warming of the Atlantic Ocean have created severe droughts in the tropics, causing major impacts on forests."

How the changes affect individual plant species in the area remains to be seen. For example, drier conditions may favor deciduous trees at the expense of evergreen trees.

"Our assessment is a step toward an improved understanding of how African rainforests respond to increasing drought," Zhou said. "We need to consider the complex range of processes affecting different tropical rainforest species before we can fully assess the future resilience of tropical forests."

Image credit: NASA/Goddard Space Flight Center Scientific Visualization Studio

Copenhagen, Denmark

The theme for Earth Day 2014 is 'green cities.' As more and more people move to cities in search of jobs – and the reality of climate change becomes increasingly clear – the need to create sustainable communities is more important than ever. Recognized this year as the European Green Capital, Copenhagen has set a prime example with investments in sustainable technology, forward-thinking public policy and an educated and active public. The Danish city is a good model in terms of urban planning and design, and is working towards becoming carbon-neutral by the year 2025.

This SPOT-5 image was acquired 21 April 2011, with a resolution of 2.5 m.

Photo credit: Airbus Defence and Space

The Grand Canyon

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of the Colorado River canyon and its many side canyons make an intricate landscape that contrasts with the dark green, forested plateau to the north and south.

The Colorado River has done all the erosional work of carving away cubic kilometers of rock in a geologically short period of time. Visible as a darker line snaking along the bottom of the canyon, the river lies at an altitude of 715 meters (2,345 feet), thousands of meters below the North and South Rims. Temperatures are furnace-like on the river banks in the summer. But Grand Canyon Village, the classic outlook point for visitors, enjoys a milder climate at an altitude of 2,100 meters (6,890 feet).

The Grand Canyon has become a geologic icon — a place where you can almost sense the invisible tectonic forces within the Earth. The North and South Rims are part of the Kaibab Plateau, a gentle tectonic swell in the landscape. The uplift of the plateau had two pronounced effects on the landscape that show up in this image. First, in drier parts of the world, forests usually indicate higher places; higher altitudes are cooler and wetter, conditions that allow trees to grow. The other geologic lesson on view is the canyon itself. Geologists now know that a river can cut a canyon only if the Earth surface rises vertically. If such uplift is not rapid, a river can maintain its course by eroding huge quantities of rock and forming a canyon.

This astronaut photograph (ISS039-E-5258) was taken on March 25, 2014 by the Expedition 39 crew, with a Nikon D3S digital camera using a 180 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. It has been cropped and enhanced to improve contrast, and lens artifacts have been removed.

Image credit: NASA

Unexpected Teleconnections in Noctilucent Clouds

Earth's poles are separated by four oceans, six continents and more than 12,000 nautical miles.

Turns out, that's not so far apart.

New data from NASA's AIM spacecraft have revealed "teleconnections" in Earth's atmosphere that stretch all the way from the North Pole to the South Pole and back again, linking weather and climate more closely than simple geography would suggest.

For example, says Cora Randall, AIM science team member and Chair of the Department of Atmospheric and Oceanic Sciences at the University of Colorado, "we have found that the winter air temperature in Indianapolis, Indiana, is well correlated with the frequency of noctilucent clouds over Antarctica."

Noctilucent clouds, or "NLCs," are Earth's highest clouds. They form at the edge of space 83 km above our planet's polar regions in a layer of the atmosphere called the mesosphere. Seeded by "meteor smoke," NLCs are made of tiny ice crystals that glow electric blue when sunlight lances through their cloud-tops.

AIM was launched in 2007 to investigate these "night-shining" clouds, to discover how they form and to learn about their inner chemistry. As is often the case, however, when exploring the unknown, researchers found something they weren't even looking for: teleconnections.

"It has been a surprise," says Hampton University professor of atmospheric and planetary science James Russell, Principal Investigator of the AIM mission. "Years ago when we were planning the AIM mission, our attention was focused on a narrow layer of the atmosphere where NLCs form. Now we are finding out this layer manifests evidence of long-distance connections in the atmosphere far from the NLCs themselves."

One of these teleconnections links the Arctic stratosphere with the Antarctic mesosphere.

"Stratospheric winds over the Arctic control circulation in the mesosphere," explains Randall. "When northern stratospheric winds slow down, a ripple effect around the globe causes the southern mesosphere to become warmer and drier, leading to fewer NLCs. When northern winds pick up again, the southern mesosphere becomes colder and wetter, and the NLCs return."

This January, a time of year when southern NLCs are usually abundant, the AIM spacecraft observed a sudden and unexpected decline in the clouds. Interestingly, about two weeks earlier, winds in the Arctic stratosphere were strongly perturbed, leading to a distorted polar vortex.

"We believe that this triggered a ripple effect that led to a decline in noctilucent clouds half-way around the world," says Laura Holt of the University of Colorado's Laboratory for Atmospheric and Space Physics. "This is the same polar vortex that made headlines this winter when parts of the USA experienced crippling cold and ice."

Holt took a careful look at meteorological data and found that, indeed, there was a statistical link between winter weather in the USA and the decline in noctilucent clouds over Antarctica.

"We picked Indianapolis as an example, because I have family living there," says Randall, "but the same was true of many northern cities: cold air temperatures on the ground were correlated with NLC frequencies high above Antarctica two weeks later," she says.

The two week delay is, apparently, how much time it takes for the teleconnection signal to propagate through three layers of atmosphere (the troposphere, stratosphere and mesosphere), and from pole to pole.

It is a complicated topic, but this much is clear: "NLCs are a valuable resource for studying long-distance connections in the atmosphere," says Russell, "and we are just getting started."

Video credit: NASA

Brussels, Belgium

Acquired on 12 April 2014 at 17:18 GMT (19:18 CEST), just nine days after launch, this first image from Sentinel-1A captures Brussels and surrounds in Belgium. It was acquired in the satellite’s ‘strip map’ mode, which has a swath width of 80 km, and in dual polarization. The image also shows a more detailed view of the city in the ‘zoom in’. Antwerp harbour is also visible in the top left. The green colors correspond to vegetation, red–blue to urban areas, white to high-density urban areas and black to waterways and low-reflective areas such as airport runways.

Image credit: ESA

Flooding from the Zambezi River in Namibia

Acquired on 13 April 2014 at 03:50 GMT (05:50 CEST) by Sentinel-1A, this image shows the extent of flooding in the Caprivi plain from the Zambezi River in Namibia. Sentinel-1A acquired this image in its main ‘Interferometric Wide Swath’ mode with a swath width of 250 km and in dual polarization. Victoria Falls is also featured in the image, further east along the Zambezi River. The image was downloaded two hours after acquisition and the resulting products were available in less than an hour. Such images can be taken in adverse weather conditions and during the dark, demonstrating the value of Sentinel-1’s radar vision.

Image credit: ESA

Pine Island and Thwaites Glaciers, Antarctica

Acquired on 13 April 2014 at 09:03 GMT (11:03 CEST) this image covers parts of Pine Island Glacier and Thwaites Glacier in West Antarctica. This image is among the first from Sentinel-1A, which was launched on 3 April. It was acquired in ‘Interferometric Wide Swath’ mode with a swath width of 250 km and in single polarization. With Pine Island Glacier in a state of irreversible retreat, the Sentinel-1 mission is set to be an excellent tool for monitoring such glaciers as well as for providing timely information on many other aspects of the polar regions, such as sea ice and icebergs.

Image credit: ESA

Antarctica Peninsula

Acquired on 13 April 2014 at 23:57 GMT (14 April at 01:57 CEST) by Sentinel-1A, this image shows a transect over the northern part of the Antarctica Peninsula. It was acquired in the satellite’s ‘strip map’ mode with a swath width of 80 km and in dual polarization. The colors indicate how the land, ice and water reflect the radar signal differently.

Image credit: ESA

Salt Marsh, Kazakhstan

This satellite image was acquired over the edge of a salt marsh near the northeast Caspian Sea in southwestern Kazakhstan.

The Caspian Sea (not pictured) is the largest inland body of water by surface area. With an average depth of about 5 m, the northern part of the Caspian is very shallow, while the central and southern parts of the sea are much deeper. The salinity of the waters also change from north to south, being more saline in the northern, shallow waters and less in the south.

The salt marsh in the upper section of this image was once a gulf of the Caspian Sea, but fluctuating sea levels over the last decades cause it to be cut off occasionally from the main body of water and even dry up. In this image, it appears that the water has evaporated, leaving behind a white salt crust.

Rock formations dominate the central part of the image, while a plateau stretches south and east (not pictured). The visible shapes in combination with the dark color of the rocks may indicate that they are volcanic, with water erosion evident in the finger-like runoff patterns.

The grey rim between the land and salt pan comes from the sedimentary runoff from the land mixing with the saltwater. When the marsh is dry, a greyish color is left behind.

The arid climate in this region makes it easy to acquire optical imagery from satellites, without the obstruction of visibility by clouds.

This image was acquired on 6 November 2012 by the Korea Aerospace Research Institute’s Kompsat-2 satellite and is featured on the Earth from Space video program.

Photo credit: KARI/ESA

Liftoff of Sentinel-1A

Cameras mounted on the Soyuz Fregat upper stage that sent Sentinel-1A into space on 3 April 2014 captured this footage from liftoff to separation.

The 2.3-ton satellite lifted off on a Soyuz rocket from Europe’s Spaceport in Kourou, French Guiana at 21:02 GMT (23:02 CEST). The first stage separated 118 sec later, followed by the fairing (209 sec), stage 2 (287 sec) and the upper assembly (526 sec). After a 617 sec burn, the Fregat upper stage delivered Sentinel into a Sun-synchronous orbit at 693 km altitude. The satellite separated from the upper stage 23 min 24 sec after liftoff.

Sentinel-1 is the first in the family of satellites for Europe’s Copernicus program. It carries an advanced radar to scan Earth’s surface in all weather conditions and regardless of whether it is day or night. This new mission will be used to care for many aspects of our environment, from detecting and tracking oil spills and mapping sea ice to monitoring movement in land surfaces and mapping changes in the way land is used.

Video credit: Arianespace/ESA/Roscosmos; Music written by M. Oldfield/copyright EMI Virgin

Update: A slightly longer version of the video can be found here: Onboard Cameras Show Full Launch and Separation of Sentinel-1A.

Guitar-Shaped Memorial Forest in Argentina

Located in the fertile agricultural region of Argentina's Pampas is a guitar-shaped forest made up of cypress and eucalyptus trees. An Argentinian farmer planted the forest in memory of his departed wife. The image was acquired November 2, 2007, covers an area of 10.2 by 12.3 km, and is located at 33.9 degrees south, 64 degrees west.

Image credit: NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team

Arctic Melt Season Lengthens

A new study by researchers from the National Snow and Ice Data Center (NSIDC) and NASA shows that the length of the melt season for Arctic sea ice is growing by several days each decade. An earlier start to the melt season is allowing the Arctic Ocean to absorb enough additional solar radiation in some places to melt as much as four feet of the Arctic ice cap’s thickness.

"The Arctic is warming and this is causing the melt season to last longer," said Julienne Stroeve, a senior scientist at NSIDC, Boulder and lead author of the new study, which has been accepted for publication in Geophysical Research Letters. "The lengthening of the melt season is allowing for more of the sun’s energy to get stored in the ocean and increase ice melt during the summer, overall weakening the sea ice cover."

Arctic sea ice has been in sharp decline during the last four decades. The sea ice cover is shrinking and thinning, making scientists think an ice-free Arctic Ocean during the summer might be reached this century. The seven lowest September sea ice extents in the satellite record have all occurred in the past seven years.

To study the evolution of sea ice melt onset and freeze-up dates from 1979 to the present day, Stroeve’s team used passive microwave data from NASA’s Nimbus-7 Scanning Multichannel Microwave Radiometer, and the Special Sensor Microwave/Imager and the Special Sensor Microwave Imager and Sounder carried on board Defense Meteorological Satellite Program spacecraft. When ice and snow begin to melt, the presence of water causes spikes in the microwave radiation that the snow grains emit, which these sensors can detect.

Results show that although the melt season is lengthening at both ends, with an earlier melt onset in the spring and a later freeze-up in the fall, the predominant phenomenon extending the melting is the later start of the freeze season. Some areas, such as the Beaufort and Chukchi Seas, are freezing up between six and 11 days later per decade. Although melt onset variations are smaller, the timing of the beginning of the melt season has a larger impact on the amount of solar radiation absorbed by the ocean, because its timing coincides with when the sun is higher and brighter in the Arctic sky.

Despite large regional variations in the beginning and end of the melt season, the Arctic melt season has lengthened on average by five days per decade from 1979 to 2013.

Video credit: NASA

Cento, Italy

Hundreds of fields speckle the northern Italian landscape south of the Po River in this satellite image.

Agriculture is one of the main economic uses of the Po Basin because of the fertile soils, and this image clearly shows a landscape dominated by fields.

Throughout Italy’s history, agricultural landowners would often divide their properties among their male heirs. Generation after generation, land would be further fragmented, resulting in the millions of small plots found across the country today.

Optical satellite imagery like this can be used to monitor agriculture and changing landscapes. Satellites can provide the information necessary to make informed decisions on agricultural management, including yield prediction, irrigation, planting, pricing and regional need for food assistance if a harvest is likely to fail.

At the very bottom of the image, foothills of the Apennine mountains appear dark green.

The city of Bologna is visible in the lower-right corner, and Modena can be seen on the left. Two roads cutting across the flat Po Valley provide a nearly straight route between the cities.

The city of Cento – which means ‘hundred’ in Italian – is located in the upper-right section of the image on the Reno river.

This image, captured by Japan’s ALOS satellite on 4 July 2010, was selected to mark the 100th regular edition of the Earth from Space video program, which we launched in November 2011.

Photo credit: JAXA/ESA

Italy

Astronauts on the International Space Station fly over our planet at around 300 km altitude. From that distance it is not always easy to distinguish countries and cities – political borders cannot be seen from space. This image however clearly shows Italy’s distinctive outline as it contrasts with the blackness of the Mediterranean Sea at night.

The lights to the north of Italy that houses much industry stop more or less at the border with France, Switzerland and Austria. The cities of Turin and Milan show up brightly, as do Rome and Naples further to the south.

The island of Sicily can be seen at the bottom-right of this image with Italy’s other large island, Sardinia, to the left. Above, and almost touching Sardinia, is the island of Corsica that is not part of Italy.

The line of lights following the northern contours of the Mediterranean Sea is the French coastline known as the ‘Côte d’Azur’ or French Riviera.

The thin green line following Earth’s curve is our atmosphere that keeps us warm, protects us from the Sun and cosmic rays as well as the vacuum of space. These images from space show how populated and industrialized Europe is and the enormous impact humans have on our planet.

Photo credit: ESA/NASA

Orbiting Carbon Observatory-2 (OCO-2)

Technicians prep the OCO-2 instrument for shipping at JPL. The instrument consists of three parallel, high-resolution spectrometers, integrated into a common structure and fed by a common telescope. Each spectrometer spreads reflected sunlight into its various colors like a prism, focusing on a different, narrow color range to detect light with the specific colors absorbed by carbon dioxide and molecular oxygen. The amount of light absorbed at these specific colors is proportional to the concentration of carbon dioxide in the atmosphere.

Image credit: NASA/JPL-Caltech

Note: For more information, see NASA's OCO-2 Brings Sharp Focus on Global Carbon.

Surface Displacement Map for 28 March 2014 La Habra Earthquake

Scientists at NASA's Jet Propulsion Laboratory, Pasadena, California, developed a model of the March 28, 2014, magnitude 5.1 La Habra, California earthquake, based on the distribution of aftershocks and other seismic information from the U.S. Geological Survey. This image shows what the earthquake may look like to an interferometric synthetic aperture radar, such as NASA's Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR).

The earthquake is believed to be associated with the Puente Hills Thrust fault, which zig-zags from Orange County northwest through downtown Los Angeles. The NASA model is based on a fault estimated to be 9 kilometers long, 5 kilometers deep and 3 kilometers wide. The modeled fault dips upward through the ground at a 60-degree angle, with one side of the fault moving at a slanted angle horizontally and vertically 10 centimeters relative to the other side. The model estimated the maximum displacement of Earth's surface from the quake at approximately 1 centimeter, which is at the threshold of what is detectable with UAVSAR. The region of ground displacement is indicated by the darker blue area located in the right center of the image.

In November 2008, NASA JPL scientists began conducting a series of UAVSAR flights over regions of Northern and Southern California that are actively deforming and are marked by frequent earthquakes. About every six months, the scientists precisely repeat the same flight paths to produce images of ground deformation called interferograms. From these data, 3-D maps are being created for regions of interest, including the San Andreas and other California faults, extending from the Gulf of California in Mexico to Santa Rosa in the northern San Francisco Bay.

UAVSAR, which flies on a NASA C20-A III aircraft from NASA's Armstrong Flight Research Center, measures ground deformation over large areas to a precision of 0.1 to 0.5 centimeters (0.04 to 0.2 inches).

By comparing the repeat-pass radar observations, scientists hope to measure any crustal deformations that may occur between observations, allowing them to 'see' the amount of strain building up on fault lines, and giving them a clearer picture of which faults are active and at what rates they're moving, both before earthquakes and after them. The UAVSAR fault mapping project is designed to substantially improve knowledge of regional earthquake hazards in California. The 3-D UAVSAR data will allow scientists to bring entire faults into focus, allowing them to understand faults not just at their surfaces, but also at depth. When integrated into computer models, the data should give scientists a much clearer picture of California's complex fault systems.

The scientists are estimating the total displacement occurring in each region. As additional observations are collected, they expect to be able to determine how strain is partitioned between individual faults.

The UAVSAR flights serve as a baseline for pre-earthquake activity. As earthquakes occur during the course of this project, the team is measuring the deformation at the time of the earthquakes to determine the distribution of slip on the faults, and then monitoring longer-term motions after the earthquakes to learn more about fault zone properties.

Airborne UAVSAR mapping can allow a rapid response after an earthquake to determine what fault was the source and which parts of the fault slipped during the earthquake. Information about the earthquake source can be used to estimate what areas were most affected by the earthquake shaking to guide rescue and damage assessment response.

The scientists now plan to acquire UAVSAR data from the region, possibly as soon as this week, and process the data to validate and improve the results of their model.

Image credit: NASA/JPL-Caltech/USGS/Google Earth

Note: For more information, see NASA Model Provides a 3-D Look at L.A.-area Quake.

Satellite Shows High Productivity from U.S. Corn Belt

The magnitude of fluorescence portrayed in this visualization prompted researchers to take a closer look at the productivity of the U.S. Corn Belt. The glow represents fluorescence measured from land plants in early July, over a period from 2007 to 2011.

Data from satellite sensors show that during the Northern Hemisphere's growing season, the Midwest region of the United States boasts more photosynthetic activity than any other spot on Earth, according to NASA and university scientists.

Healthy plants convert light to energy via photosynthesis, but chlorophyll also emits a fraction of absorbed light as a fluorescent glow that is invisible to the naked eye. The magnitude of the glow is an excellent indicator of the amount of photosynthesis, or gross productivity, of plants in a given region.

Research in 2013, led by Joanna Joiner of NASA's Goddard Space Flight Center in Greenbelt, Maryland, demonstrated that fluorescence from plants could be teased out from existing data from satellites that were designed and built for other purposes. The new research, led by Luis Guanter of the Freie Universität Berlin, used the data for the first time to estimate photosynthesis from agriculture. Results were published March 25 in the Proceedings of the National Academy of Sciences.

According to co-author Christian Frankenberg of NASA's Jet Propulsion Laboratory in Pasadena, Calif., "The paper shows that fluorescence is a much better proxy for agricultural productivity than anything we've had before. This can go a long way regarding monitoring -- and maybe even predicting -- regional crop yields."

Guanter, Joiner and Frankenberg launched their collaboration at a 2012 workshop, hosted by the Keck Institute for Space Studies at the California Institute of Technology (Caltech) in Pasadena, to explore measurements of photosynthesis from space. The team noticed that on an annual basis, the tropics are the most active in photosynthesis. But during the Northern Hemisphere's growing season, the U.S. Corn Belt "really stands out," Frankenberg said. "Areas all over the world are not as productive as this area."

The researchers set out to describe the phenomenon observed by carefully interpreting data from the Global Ozone Monitoring Experiment 2 (GOME-2) on Metop-A, a European meteorological satellite. Data showed that fluorescence from the U.S. Corn Belt peaks in July at levels 40 percent greater than those observed in the Amazon.

Comparison with ground-based measurements from carbon flux towers and yield statistics confirmed the results.

"The match between ground-based measurements and satellite measurements was a pleasant surprise," said Joiner, a co-author on the paper.

Ground-based measurements have a resolution of about 0.4 square mile (1 square kilometer), while the satellite measurements currently have a resolution of more than 1,158 square miles (3,000 square kilometers). The study confirms that even with coarse resolution, the satellite method could estimate the photosynthetic activity occurring inside plants at the molecular level for areas with relatively homogenous vegetation like the Corn Belt.

Challenges remain in estimating the productivity of fragmented agricultural areas not properly sampled by current space-borne instruments. That's where missions with better resolution could help, such as NASA's Orbiting Carbon Observatory-2 (OCO-2) -- a mission planned for launch in July 2014 that will also measure solar-induced fluorescence.

The research could also help scientists improve the computer models that simulate Earth's carbon cycle, as Guanter found a strong underestimation of crop photosynthesis in models. The analysis revealed that carbon cycle models -- which scientists use to understand how carbon cycles through the ocean, land and atmosphere over time -- underestimate the productivity of the U.S. Corn Belt by 40 to 60 percent.

Unlike most vegetation, food crops are managed to maximize productivity. They usually have access to abundant nutrients and are irrigated. The U.S. Corn Belt, for example, receives water from the Mississippi River. Accounting for the region's irrigation is currently a challenge for models, which is one reason why they underestimate agricultural productivity.

"If we don't take into account irrigation and other human influences in the agricultural areas, we're not going to correctly estimate the amount of carbon taken up by vegetation, particularly corn," Joiner said. "Corn plants are very productive in terms of assimilating carbon dioxide from the atmosphere. This needs to be accounted for going forward in trying to predict how much of the atmospheric carbon dioxide will be taken up by crops in a changing climate."

According to Frankenberg, the remote sensing-based techniques now available could be a powerful monitoring tool for food security, especially data from OCO-2 in combination with data from other upcoming satellites such as NASA's Soil Moisture Active Passive (SMAP), scheduled for launch later this year.

Image credit: NASA's Goddard Space Flight Center