Some Insight on the Color of the Ocean

September 28th, 2015 by Mike Carlowicz

For nearly 20 years, Jim Acker, a contract support scientist at the NASA Goddard Earth Science Data and Information Services Center (GES DISC), has helped oceanographers compile and study data collected by satellites. A chemical oceanographer by training, he has been involved in the study of ocean color as viewed from space. He recently wrote a book for NASA about the history of the subject. He is also scheduled to deliver the NASA Goddard Science Colloquium on September 30 at 3:30 p.m. His talk is entitled: “Rise of the Machines: Computational Power and the History of NASA’s Ocean Color Missions.” He gave us a preview of the book and the talk this week.

NASA Earth Observatory: Most of us think of the ocean as blue; in some places, it looks green. So what do scientists mean when they refer to “ocean color?”

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Jim Acker: Well, it’s blue and green and brown, and occasionally a few other related hues. Ocean color refers to the science of using satellite sensors to measure the light emanating from the ocean and determining what is in the water based on those light measurements. The main things that change the color of the ocean are phytoplankton—the floating plants at the base of the ocean food chain—dissolved colored substances, and different kinds of sediments.

EO: What are some of the things we have learned by looking at the ocean from satellites?

Acker: One of the main things done with global observations has been estimating how much carbon is produced by the growth of phytoplankton. Ocean color observations have shown how much this can vary, particularly with events like El Niño or La Niña in the Pacific Ocean.

The satellite view also can show how much variation there is over relatively short distances. A ship could be sitting in nice clear water, and just a few tens of kilometers away there could be a strong phytoplankton bloom that they would never know about without observations from space.

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The observations also have helped understand phytoplankton patterns in hard-to-reach places like the polar seas and the Red Sea or Arabian Sea. The interaction of the land and ocean, with weather patterns and river inflows, has also been better observed.

EO: Have there been any big surprises?

Acker: Definitely. One of the biggest surprises from the Coastal Zone Color Scanner, the first NASA ocean color mission, was truly how much the ocean varied over small distances. Where oceanographers used to draw simple lines, they realized there were swirls and spirals and curlicues and loops and jets and rings. It was much more complicated.

Another surprise when SeaWiFS and MODIS started making global observations was how cloudy it is over the oceans.  It takes really impressive data processing to get accurate values because of that.

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And because the satellites make continuous observations, they have observed many different features that weren’t where we expected them to be or they happened more often than we thought.

EO: What provoked you to write a book?

Acker: NASA wanted to have some histories of NASA science, and I wanted to tell the history of ocean color because it’s been so successful. It’s like a well-trained, elite athlete:  they make what they do look easy, though a lot of hard effort and training makes that possible.

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Ocean color measurements are very difficult to make, but because the missions have been so successful, the public and even most scientists have just seen the beautiful results and have not realized the dedicated, behind-the-scenes work that made them possible. It isn’t just about seeing images from space on a computer monitor. To be sure the data is accurate, there have been some true high-seas adventures. I was able to get a lot of real-life experiences from the scientists and engineers into the book.

EO: What is your favorite book about science?  And your favorite writer?

Acker: My favorite book that was sort of about science was The Map that Changed the World by Simon Winchester; I also enjoyed his book about the eruption of Krakatoa. My favorite writers are Pat Conroy and J.R.R. Tolkien. The late Stephen Jay Gould wrote a lot of things about science I liked.  And I have to mention that I just read Andy Weir’s The Martian and was quite impressed. I’m looking forward to seeing the movie.

 

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September Puzzler

September 22nd, 2015 by Kathryn Hansen

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Every month on Earth Matters, we offer a puzzling satellite image. The September 2015 puzzler is above. Your challenge is to use the comments section to tell us what part of the world we are looking at, when the image was acquired, what the image shows, and why the scene is interesting.

How to answer. Your answer can be a few words or several paragraphs. (Try to keep it shorter than 200 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure speck in the far corner of an image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money, but, we can promise you credit and glory (well, maybe just credit). Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. In the credits, we’ll acknowledge the person who was first to correctly ID the image. We’ll also recognize people who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have played a role in molding the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you want us to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the last few months or work in geospatial imaging, please sit on your hands for at least a day to give others a chance to play.

Releasing Comments. Savvy readers have solved some of our puzzlers after only a few minutes or hours. To give more people a chance to play, we may wait between 24-48 hours before posting the answers we receive in the comment thread.

Good luck!

August Puzzler Answer: Bloom in the Baltic Sea

August 26th, 2015 by Kathryn Hansen

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When I first saw the image for the August puzzler, I was struck by its beauty. The blue-green swirls look like they could be the brush strokes of an impressionist painting. Instead, this false-color scene was acquired by the Operational Land Imager (OLI) on Landsat 8.

Without any land visible in the scene, I thought it would be at least a day or two before receiving a correct guess. I was wrong. Congratulations to Helen Macintyre who was the first to correctly post a correct answer to the blog on August 18, just 94 minutes after the puzzler was posted.

Macintyre wrote, “Initially I thought hurricane, but the strands in the upper left seem too sharp and thin. I think this is an algal bloom swirling in ocean currents. The line near the top I think is a large ocean liner cutting through this, leaving a darker colored wake.”

Indeed, the scene shows a phytoplankton bloom. This particular bloom contains cyanobacteria—an ancient type of marine bacteria that, like other phytoplankton, capture and store solar energy through photosynthesis.

Later that same day, Kari Nöjd posted a comment and became the first to correctly guess the phenomenon and its location. In fact, Nöjd was the only participant to correctly place this bloom in the Baltic Sea. Excellent work!

Nöjd wrote, “My guess is that this picture shows sea surface where algae is blooming. The line is from the boat, which is driving through the sea surface. Picture could have been taken from the Baltic Sea where has been big algae blooming fields forming for the past month … Unfortunately this is also effect of a human behavior. Nutrients from fields and waste waters increase the algae blooming.”

According to NASA oceanographer Norman Kuring, major cyanobacteria blooms like this one appear in the Baltic Sea nearly every summer, “and they always look like this in the satellite data.” Physical measurements from an expert in the field, however, were required to confirm that the bloom was cyanobacteria.

As for the line cutting through the scene? Yes, that’s the result of a ship cruising through the bloom. There are other ships too, as well as an airplane, visible in the zoomed-out version posted in our August 23, 2015, Image of the Day.

On Facebook, Scot Hoffman was the first to guess algae bloom. In fact, a lot of comments on Facebook noted that the scene was a bloom, but the location remained elusive. Many thought it might be Lake Erie—a good guess because blooms are visible during the summer in that lake as well.

August Puzzler

August 18th, 2015 by Kathryn Hansen

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Every month on Earth Matters, we offer a puzzling satellite image. The August 2015 puzzler is above. Your challenge is to use the comments section to tell us what part of the world we are looking at, when the image was acquired, what the image shows, and why the scene is interesting.

How to answer. Your answer can be a few words or several paragraphs. (Try to keep it shorter than 200 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure speck in the far corner of an image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money, but, we can promise you credit and glory (well, maybe just credit). Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. In the credits, we’ll acknowledge the person who was first to correctly ID the image. We’ll also recognize people who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have played a role in molding the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you want us to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the last few months or work in geospatial imaging, please sit on your hands for at least a day to give others a chance to play.

Releasing Comments. Savvy readers have solved some of our puzzlers after only a few minutes or hours. To give more people a chance to play, we may wait between 24-48 hours before posting the answers we receive in the comment thread.

Good luck!

July Puzzler Answer: Forests of the Cal Madow

July 31st, 2015 by Adam Voiland
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This image was acquired on June 27, 2015, by the Operational Land Imager on Landsat 8. Read more about the image here.

What was that brain-like pattern featured in our July puzzler and how did it form? The key insight—which none of the hundreds of readers who commented mentioned—was that the pattern was caused by a network of stream valleys and bands of vegetation that follow the contour of the hills. (Read our July 26 Image of the Day to find out why the vegetation grows in bands.) However, reader Stephanie Wurdinger did nail the location on both Facebook and our Earth Matter blog. “This is along the north coast of Somalia between Dayaha and Maydh, in Sanaag region. Mt Shimbiris is just off the upper right hand corner of this image. I believe it is part of the Maydh greenstone belt,” she wrote.

One of the more interesting things about the forests of the Cal Madow is that they are important sources of frankincense and myrrh, the fragrant resins made famous by the Biblical account of three kings bringing them to Bethlehem as gifts. For a more modern take on the frankincense and myrrh trade, check out the video put together by the the Institute for Environmental Diplomacy and Security at the University of Vermont. Skip ahead to mintute 2:30 to join the producers as they bump over rough mountain roads in Somaliland looking for frankincense. The same organization has posted a report about the frankincense industry in Somaliland with many more details.

July Puzzler

July 21st, 2015 by Adam Voiland

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Every month on Earth Matters, we offer a puzzling satellite image. The July 2015 puzzler is above. Your challenge is to use the comments section to tell us what part of the world we are looking at, when the image was acquired, what the image shows, and why the scene is interesting.

How to answer. Your answer can be a few words or several paragraphs. (Try to keep it shorter than 200 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure speck in the far corner of an image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money, but, we can promise you credit and glory (well, maybe just credit). Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. In the credits, we’ll acknowledge the person who was first to correctly ID the image. We’ll also recognize people who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have played a role in molding the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you want us to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the last few months or work in geospatial imaging, please sit on your hands for at least a day to give others a chance to play.

Releasing Comments. Savvy readers have solved some of our puzzlers after only a few minutes or hours. To give more people a chance to play, we may wait between 24-48 hours before posting the answers we receive in the comment thread.

Good luck!

This is a cross-post from Laura Rocchio and our colleagues at NASA’s Landsat Science Team.

The European Space Agency’s Sentinel-2A successfully launched into orbit on June 22, 2015, from Europe’s Spaceport in Kourou, French Guiana, aboard a Vega rocket (10:52 p.m. local time; 01:52 GMT).

The Sentinel-2A satellite has spectral bands similar to Landsat 8’s (excluding the thermal bands of Landsat 8’s Thermal Infrared Sensor). The placement of the Sentinel-2A bands, as compared to Landsat 8 and Landsat 7 bands, can be seen in the graphic below.

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The main visible and near-infrared Sentinel-2A bands have a spatial resolution of 10 meters, while its “red-edge” (red and near-infrared bands)—specifically designed to monitor vegetation—along with its two shortwave infrared bands have a 20-meter spatial resolution, and its coastal/aerosol, water vapor, and cirrus bands have a 60-meter spatial resolution.

During the development of Landsat 8 and Sentinel-2A, calibration scientists from both projects worked together to cross-calibrate the sensors. Many scientists and researchers are looking forward to collectively using data from Landsat 8 and Sentinel-2A.

Sentinel-2A alone provides 10-day repeat coverage of Earth’s land areas. In combination with the 8-day coverage from Landsat 7 and 8 combined, users can look forward to better-than-weekly coverage at moderate resolution. Repeat coverage capabilities will further increase with the planned launch of a second Sentinel-2 satellite (Sentinel-2B) in 2016.

According to ESA, “As well as monitoring plant growth, Sentinel-2 will be used to map changes in land cover and to monitor the world’s forests. It will also provide information on pollution in lakes and coastal waters. Images of floods, volcanic eruptions and landslides will contribute to disaster mapping and helping humanitarian relief efforts.”

After the successful Sentinel-2A launch, Dr. Garik Gutman, the NASA Land Use / Land Cover Change program manager, said, “We are looking forward to new exciting data to complement Landsat observations and to collaborative research—especially because ESA followed USGS in its open data policy.” This sentiment is echoed by many in the Landsat community.

Read more about Sentinel 2A by clicking here

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Our July 16 Image of the Day—Changing Forest Cover Since the Soviet Era—features a Landsat-derived map showing how forests have changed in Eastern Europe since 1985. After exploring the three areas we highlighted, I highly recommend browsing the map at full resolution using either Google Earth or GigaPan. The amount of detail you will find is extraordinary. There are dozens of other interesting forest loss and gain hot spots that we could have highlighted. In fact, we may publish additional stories using these data, so please let us know if you are aware of local stories of forest change in eastern Europe that deserve more attention.

While the satellite maps offer invaluable “big picture” perspective, ground photographs really bring the changes to life. Peter Potapov, the University of Maryland scientist who led the mapping effort, passed along a few photographs taken during his field research in Russia. It is one thing to know that a brown pixel in the maps indicate forest loss and the a green pixel indicates gain. It becomes real when you can actually see charred trunks after a forest fire or stands of saplings springing up in abandoned Soviet farm fields.

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Logging site in the Vladimir region of Russia. Photo Credit: Peter Potapov.

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Spruce trees killed by bark beetle in the Vladimir region of Russia. Photo Credit: Peter Potapov.

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Charred trunks caused by a forest fire in the Vladimer region of Russia. Photo credit: Peter Potapov

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Pine forests in an abandoned pasture in the Vladimir region of Russia. The pine trees are about ten years old. Photo Credit: Peter Potapov.

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Birch forest growing on abandoned farmland in the Nizhny Novgorod region of Russia. Photo Credit: Peter Potopov

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Early stages of forest recovery in abandoned farmland in the Kirov region of Russia. Photo Credit: Peter Potapov

Seismic Surveying (Not Nazca) Lines

July 1st, 2015 by Adam Voiland

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Many readers were convinced that our June Puzzler (image above) showed Nazca lines in southern Peru. There certainly were lines in the image, but they were located about 10,000 kilometers (6,000 miles) away from Peru on a plateau in southern Libya. While the Nazca lines were probably created for religious purposes, the grid lines in Libya had a very different raison d’être: oil exploration.

As Stefano correctly noted at 12:26 p.m. on June 23, the lines were tracks left over from a seismic survey. While a layer of rocks, gravel, and ancient stone tools carpet most of the plateau, lines of large “thumper” trucks that use a vibrating metal plate to press down against the ground likely created the grid pattern. When they drove around prospecting the area with seismic sensors, the trucks kicked up a very fine layer of dust that was lighter brown than the rest of the surface. Less than two hours after Stefano weighed in, Miles Saunders explained much of this.

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Nazca lines in southern Peru. Read more about them here.

Twenty minutes later, Franco B. weighed in with some more key details. “This looks like geophysical prospection lines in some oil field in an arid zone, each line would be a succession of geophones placed in order to make seismic sections. The scattered dots are probably oil wells. The combination of lines at 90º allows to make very detailed 3D maps of the geological structures in depth, in order to improve the oil and gas exploration. All this overlays on what looks like an intermittent dendritic drainage pattern, evidence of the arid climate,” he said.

To get a sense of how the “thumper” trucks work, check out the video below from Maurin Media.

Here is a view of what the tracks look like on the ground.

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Photograph courtesy of Marta Lahr, University of Cambridge.

Meanwhile, twelve minutes before Stefano mentioned seismic lines on our blog, Kaye Simonson noted on our Facebook page that the grid was related to seismographs. About ten minutes later, Chris Leonard posted the exact coordinates on Facebook. By that afternoon, Leonard had figured out that the image featured seismic grid lines related to oil exploration. He worked it out by locating an archaeological study published in PLOS One that included the telling figure shown below. As the authors of that paper explain, the top part of the figure (a) shows the location of the grid lines that were laid out for oil exploration. The middle part (b) shows where archaeologists discovered stone tools (lithics) during a sweep before the seismic survey. A white circle indicates the presence of tools; larger circles indicate a higher density of stone tools. The bottom part (c) shows a more detailed view of a small portion of the plateau.

To learn more about the area, read our June 27, 2015, Image of the Day. Thanks to all of you who participated, and a big congratulations to the winners!

 

Fine Particulate Maps With and Without Dust

June 23rd, 2015 by Adam Voiland
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Fine particulate matter (PM2.5) for 2010-2012 with dust and sea salt included. Visualization by Josh Stevens. Data from van Donkelaar et al. 

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Fine particulate matter (2.5) concentration for 2010-2012 without dust and sea salt included. Data from van Donkelaar et al.

If you saw our June 22 Image of the Day with global maps of fine particulate matter (PM2.5), you may have noticed large concentrations over the Sahara Desert and the Arabian Peninsula. With vast deserts in these areas, it’s not a surprise that the satellites detected so many particulates. Winds regularly send plumes of dust blowing over the region and even to Europe and the Americas.

However, it isn’t clear how damaging dust particles are to human health in comparison to other types of fine aerosol particles (such as those produced by burning fossil fuels or biomass burning). Several teams of epidemiologists have looked for associations between outbreaks of Saharan dust and health problems, but the results have been mixed. A literature review published in 2012 summarized the state of the science this way: “The association of fine particles PM2.5, with total or cause-specific mortality is not significant during Saharan dust intrusions. However, regarding coarser fractions PM10 and PM2.5-10, an explicit answer cannot be given. Some of the published studies state that they increase mortality during Sahara dust days while other studies find no association between mortality and PM10 or PM2.5-10. The main conclusion of this review is that health impacts of Saharan dust outbreaks needs to be further explored.”

Since dust is natural and may not have significant effects on human health, the team of Dalhousie University scientists who developed the global PM2.5 exposure maps prepared two versions of their data. One shows total PM2.5 concentration (top map above) globally; the other shows PM2.5 excluding contributions from dust and sea salt (bottom map). Notice how much less PM2.5 appears in northern Africa when dust is excluded.

To get a sense of how PM2.5 concentration (excluding dust and sea salt) has changed between 2000 and 2010, see the map below. Notice that while PM2.5 has decreased over North America and Europe, it has increased over Asia. To read more about what is driving these trends, read this story.  To learn more about the data used to create these maps, visit this website. 

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Areas where PM2.5 concentration has increased between 1998 and 2012 are shown with shades of red. Decreases are shown with shades of blue. Data from van Donkelaar et al.