February 2018 Puzzler

February 20th, 2018 by Adam Voiland

Every month on Earth Matters, we offer a puzzling satellite image. The February 2018 puzzler is above. Your challenge is to use the comments section to tell us what we are looking at, when the image was acquired, and why the scene is interesting.

How to answer. You can use a few words or several paragraphs. You might simply tell us the location. 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 feature in the image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money or a trip to Mars, 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. After we post the answer, we will acknowledge the first person to correctly identify the image at the bottom of this blog post. We also may recognize readers who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have shaped the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you would like to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the past few months or if you work in geospatial imaging, please hold your answer for at least a day to give less experienced readers a chance to play.

Releasing Comments. Savvy readers have solved some puzzlers after a few minutes. To give more people a chance to play, we may wait between 24 to 48 hours before posting comments.

Good luck!

NASA Earth Observatory readers may recognize this image of a long trail of clouds — an atmospheric river — reaching across the Pacific Ocean toward California. It appeared first as an Image of the Day about how these moisture superhighways fueled a series of drought-busting rain and snow storms.

More recently, we were pleased to see that image on the cover of the Fourth National Climate Assessment — a major report issued by the U.S. Global Research Program. That image was one of many from Earth Observatory that appeared in the report. Since the authors did not give much background about the images, here is a quick rundown of how they were created and how they fit with some of the key points on our changing climate.


Hurricanes in the Atlantic
Found in Chapter 1: Our Globally Changing Climate


What the image shows:
Three hurricanes — Katia, Irma, and Jose — marching across the Atlantic Ocean on September 6, 2017.

What the report says about tropical cyclones and climate change:
The frequency of the most intense hurricanes is projected to increase in the Atlantic and the eastern North Pacific. Sea level rise will increase the frequency and extent of extreme flooding associated with coastal storms, such as hurricanes.

How the image was made:
The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite collected the data. Earth Observatory staff combined several scenes, taken at different times, to create this composite. Original source of the image: Three Hurricanes in the Atlantic


The North Pole
Found in Chapter 2: Physical Drivers of Climate Change

What the image shows:
Clouds swirl over sea ice, glaciers, and green vegetation in the Northern Hemisphere, as seen on a spring day from an angle of 70 degrees North, 60 degrees East.

What the report says about climate change and the Arctic:
Over the past 50 years, near-surface air temperatures across Alaska and the Arctic have increased at a rate more than twice as fast as the global average. It is very likely that human activities have contributed to observed Arctic warming, sea ice loss, glacier mass loss, and a decline in snow extent in the Northern Hemisphere.

How it was made:
Ocean scientist Norman Kuring of NASA’s Goddard Space Flight Center pieced together this composite based on 15 satellite passes made by VIIRS/Suomi NPP on May 26, 2012. The spacecraft circles the Earth from pole to pole, so it took multiple passes to gather enough data to show an entire hemisphere without gaps. Original source of the image: The View from the Top


Columbia Glacier
Found in Chapter 3: Detection and Attribution of Climate Change

What the image shows:
Columbia Glacier in Alaska, one of the most rapidly changing glaciers in the world.

What the report says about Alaskan glaciers and climate change:
The collective ice mass of all Arctic glaciers has decreased every year since 1984, with significant losses in Alaska.

How the image was made:
NASA Earth Observatory visualizers made this false-color image based on data collected in 1986 by the Thematic Mapper on Landsat 5. The image combines shortwave-infrared, near-infrared, and green portions of the electromagnetic spectrum. With this combination, snow and ice appears bright cyan, vegetation is green, clouds are white or light orange, and open water is dark blue. Exposed bedrock is brown, while rocky debris on the glacier’s surface is gray. Original source of the image: World of Change: Columbia Glacier


Cloud Streets
Found in: Intro to Chapter 4: Climate Models, Scenarios, and Projections

What the image shows:
Sea ice hugging the Russian coastline and cloud streets streaming over the Bering Sea.

What the report says about clouds and climate change:
Climate feedbacks are the largest source of uncertainty in quantifying climate sensitivity — that is, how much global temperatures will change in response to the addition of more greenhouse gases to the atmosphere.

How it was made:
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image on January 4, 2012. The LANCE/EOSDIS MODIS Rapid Response Team generated the image, and NASA Earth Observatory staff cropped and labeled it. Original source of the image: Cloud streets over the Bering Sea


Extratropical Cyclones
Found in Intro to Chapter 5: Large-scale circulation and climate variability

What it shows:
Two extratropical cyclones, the cause of most winter storms, churned near each other off the coast of South Africa in 2009.

What the report says about extratropical storms and climate change:
There is uncertainty about future changes in winter extratropical cyclones. Activity is projected to change in complex ways, with increases in some regions and seasons and decreases in others. There has been a trend toward earlier snowmelt and a decrease in snowstorm frequency on the southern margins of snowy areas. Winter storm tracks have shifted northward since 1950 over the Northern Hemisphere.

How the image was made:
The Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA’s Terra satellite captured this natural-color image. The LANCE/EOSDIS MODIS Rapid Response Team generated the image and NASA Earth Observatory staff cropped and labeled it. Original source of the image: Cyclonic Clouds over the South Atlantic Ocean


Sea of Sand
Found in: Chapter 6: Temperature Changes in the United States

What the image shows: Large, linear sand dunes alternating with interdune salt flats in the Rub’ al Khali in the Sultanate of Oman.

What the report says about drought, dust storms, and climate change:
The human effect on droughts is complicated. There is little evidence for a human influence on precipitation deficits, but a lot of evidence for a human fingerprint on surface soil moisture deficits — starting with increased evapotranspiration caused by higher temperatures. Decreases in surface soil moisture over most of the United States are likely as the climate warms. Assuming no change to current water resources management, chronic hydrological drought is increasingly possible by the end of the 21st century. Changes in drought frequency or intensity will also play an important role in the strength and frequency of dust storms.

How it was made: An astronaut on the International Space Station took the photograph with a Nikon D3S digital camera using a 200 millimeter lens on May 16, 2011. Original source of the image: Ar Rub’ al Khali Sand Sea, Arabian Peninsula


Flooding on the Missouri River
Found in Chapter 7: Precipitation Change in the United States

What the image shows:
Sediment-rich flood water lingering on the Missouri River in July 2011.

What the report says about precipitation, floods, and climate change:
Detectable changes in flood frequency have occurred in parts of the United States, with a mix of increases and decreases in different regions. Extreme precipitation, one of the controlling factors in flood statistics, is observed to have generally increased and is projected to continue to do. However, scientists have not yet established a significant connection between increased river flooding and human-induced climate change.

How the image was made:
The Advanced Land Imager (ALI) on NASA’s Earth Observing-1 (EO-1) satellite captured the data for this natural-color image. NASA Earth Observatory staff processed, cropped, and labeled the image. Original source of the image: Flooding near Hamburg, Iowa


Smoke and Fire
Found in Chapter 8: Droughts, Floods, and Wildfires

What the image shows:
Smoke streaming from the Freeway fire in the Los Angeles metro area on November 16, 2008.

What the report says about wildfires and climate change:
The incidence of large forest fires in the western United States and Alaska has increased since the early 1980s and is projected to further increase as the climate warms, with profound changes to certain ecosystems. However, other factors related to climate change — such as water scarcity or insect infestations — may act to stifle future forest fire activity by reducing growth or otherwise killing trees.

How it was made: The MODIS Rapid Response Team made this image based on data collected by NASA’s Aqua satellite. Original source of the image: Fires in California


The Colorado River and Grand Canyon
Found in Chapter 10: Changes in Land Cover and Terrestrial Biogeochemistry

What the image shows:
The Grand Canyon in northern Arizona.

What the report says about climate change and the Colorado River:
The southwestern United States is projected to experience significant decreases in surface water availability, leading to runoff decreases in California, Nevada, Texas, and the Colorado River headwaters, even in the near term. Several studies focused on the Colorado River basin showed that annual runoff reductions in a warmer western U.S. climate occur through a combination of evapotranspiration increases and precipitation decreases, with the overall reduction in river flow exacerbated by human demands on the water supply.

How the image was made:
On July 14, 2011, the ASTER sensor on NASA’s Terra spacecraft collected the data used in this 3D image. NASA Earth Observatory staff made the image by draping an ASTER image over a digital elevation model produced from ASTER stereo data. Original source of the image: Grand New View of the Grand Canyon


Arctic Sea Ice
Found in Chapter 11: Arctic Changes and their Effects on Alaska and the Rest of the United States

What the image shows: A clear view of the Arctic in June 2010. Clouds swirl over sea ice, snow, and forests in the far north.

What the report says about sea ice and climate change: Since the early 1980s, annual average Arctic sea ice has decreased in extent between 3.5 percent and 4.1 percent per decade, become 4.3 to 7.5 feet (1.3 and 2.3 meters) thinner. The ice melts for at least 15 more days each year. Arctic-wide ice loss is expected to continue through the 21st century, very likely resulting in nearly sea ice-free late summers by the 2040s.

How it was made: Earth Observatory staff used data from several MODIS passes from NASA’s Aqua satellite to make this mosaic. All of the data were collected on June 28, 2010. Original source of the image: Sunny Skies Over the Arctic


Crack in the Larsen C Ice Shelf
Found in Chapter 12: Sea Level Rise

What the image shows:
This photograph shows a rift in the Larsen C Ice Shelf as observed from NASA’s DC-8 research aircraft. An iceberg the size of Delaware broke off from the ice shelf in 2017.

What the report says about ice shelves in Antarctica and climate change?
Floating ice shelves around Antarctica are losing mass at an accelerating rate. Mass loss from floating ice shelves does not directly affect global mean sea level — because that ice is already in the water — but it does lead to the faster flow of land ice into the ocean.

How it was made:
NASA scientist John Sonntag took the photo on November 10, 2016, during an Operation IceBridge flight. Original source of the image: Crack on Larsen C


The Gulf of Mexico
Found in Chapter 13: Ocean Acidification and Other Changes

What the image shows:
Suspended sediment in shallow coastal waters in the Gulf of Mexico near Louisiana.

What the report says about the Gulf of Mexico:
The western Gulf of Mexico and parts of the U.S. Atlantic Coast (south of New York) are currently experiencing significant sea level rise caused by the withdrawal of groundwater and fossil fuels. Continuation of these practices will further amplify sea level rise.

How the image was made:
The MODIS instrument on NASA’s Aqua satellite captured this natural-color image on November 10, 2009. Original source of the image: Sediment in the Gulf of Mexico


Farmland in Virginia
Found in Appendix D

What the image shows:
A fall scene showing farmland in the Page Valley of Virginia, between Shenandoah National Park and Massanutten Mountain.

What the report says about farming and climate change:
Since 1901, the consecutive number of frost-free days and the length of the growing season have increased for the seven contiguous U.S. regions used in this assessment. However, there is important variability at smaller scales, with some locations actually showing decreases of a few days to as much as one to two weeks. However, plant productivity has not increased, and future consequences of the longer growing season are uncertain.

How the image was made: On October 21, 2013, the Operational Land Imager (OLI) on Landsat 8 captured a natural-color image of these neighboring ridges. The Landsat image has been draped over a digital elevation model based on data from the ASTER sensor on the Terra satellite. Original source of the image: Contrasting Ridges in Virginia


Atmospheric River
Found on the Cover and Executive Summary

What the image shows: A tight arc of clouds stretching from Hawaii to California, which is a visible manifestation of an atmospheric river of moisture flowing into western states.

What the report says about atmospheric rivers and climate change:
The frequency and severity of land-falling atmospheric rivers on the U.S. West Coast will increase as a result of increasing evaporation and the higher atmospheric water vapor content that occurs with increasing temperature. Atmospheric rivers are narrow streams of moisture that account for 30 to 40 percent of the typical snow pack and annual precipitation along the Pacific Coast and are associated with severe flooding events.

How it was made: On February 20, 2017, the VIIRS on Suomi NPP captured this natural-color image of conditions over the northeastern Pacific. NASA Earth Observatory data visualizers stitched together two scenes to make the image. Original source of the image: River in the Sky Keeps Flowing Over the West

What Caused Twin Mega-Avalanches in Tibet?

February 6th, 2018 by Adam Voiland

In July 2016, the lower portion of a valley glacier in the Aru Range of Tibet detached and barreled into a nearby valley, killing nine people and hundreds of animals. The huge avalanche, one of the largest scientists had ever seen, sent a tongue of debris spreading across 9 square kilometers (3 square miles). With debris reaching speeds of 140 kilometers (90 miles) per hour, the avalanche was remarkably fast for its size.

(NASA Earth Observatory image by Joshua Stevens, using modified Copernicus Sentinel 2 data processed by the European Space Agency. Image collected on July 21, 2016.)

Researchers were initially baffled about how it had happened. The glacier was on a nearly flat slope that was too shallow to cause avalanches, especially fast-moving ones. What’s more, the collapse happened at an elevation where permafrost was widespread; it should have securely anchored the glacier to the surface.

Two months later, it happened again — this time to a glacier just a few kilometers away. One gigantic avalanche was unusual; two in a row was unprecedented. The second collapse raised even more questions. Had an earthquake played a role in triggering them? Did climate change play a role? Should we expect more of these mega-avalanches?

(NASA Earth Observatory image by Joshua Stevens and Jesse Allen, using ASTER data from NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Image collected on October 4, 2016.)

Now scientists have answers about how these unusual avalanches happened. There were four factors that came together and triggered the collapses, an international team of researchers reported in Nature Geoscience. The scientists analyzed many types of satellite, meteorological, and seismic data to reach their conclusions. They also sent teams of researchers to investigate the avalanches in the field.

First, increasing snowfall since the mid-1990s caused snow to pile up and start working its way toward the front edge of the glaciers (a process known as surging). Second, a great deal of rain fell in the summer of 2016. As a result, water worked its way through crevasses on the surface and lubricated the undersides of the glaciers. Third, water pooled up underneath the glaciers, even as the edges remained frozen to the ground. Fourth, the glaciers sat on a fine-grained layer of siltstone and clay that became extremely slippery.

Notice the large amounts of silt and clay in the path of the first avalanche. (Photo taken on July 15, 2017, by Adrien Gilbert/University of Oslo)

Earth Observatory checked in with Andreas Kääb (University of Oslo),  lead author of the study, to find out more about how the avalanche happened and what it means.

These glaciers were not on a steep slope, but the avalanche moved quite quickly. How did that happen?
Strong resistance by the frozen margins and tongues of the glaciers allowed the pressure to build instead of enabling them to adjust. The glaciers were loading up more and more pressure until the frozen margins suddenly failed. Local people reported a load bang. Once the margins failed, there was nothing at the glacier bed to hold it back, just water-soaked clay.

Your study notes that there was “undestroyed grassy vegetation on the lee side of the hills, suggesting that the fast-moving mass had partially jumped over it.” Are you saying the avalanche was airborne? If so, is that unusual?
Yes, for a small part of the avalanche path. We see this for other large-volume, high-speed avalanches, and it really illustrates the massive amount of energy released. You need quite high speeds in order for debris to jump. For us, the phenomenon is important as validation for the speeds obtained from the seismic signals the avalanches triggered and the avalanche modeling that we did.

Would you say these collapses were a product of climate change?
Climate change was necessary, but other factors that had nothing to do with climate were also critical. The increasing mass of the glaciers since the 1990s and the heavy rains and meltwater in 2016 are connected to climate change. The type of bedrock and the way the edges were frozen to the ground had nothing to do with climate change.

Can we expect to see more big glacial collapses as the world gets warmer?
It’s not clear. Climate change could increase or, maybe even more likely, decrease the probability of such massive collapses. Most glaciers on Earth are actually losing mass (not gaining, like the two glaciers in Tibet were). Also, if permafrost becomes less widespread over time and glacier margins melt, it is less likely that pressure will build up in that way that it did in this case.

I know you used several types of satellite data as part of this analysis. Can you mention a few that yielded particularly useful information?
We used a lot of different sources of data: Sentinel 1 and 2, TerraSAR-X/TanDEM-X, Planet Labs, and DigitalGlobe WorldView. Landsat 8 was absolutely critical because it gave the first and critical indication of the soft-bed characteristics. The entire Landsat series was instrumental for checking the glacier history since the 1980s. We also used declassified Corona data back to the 1960s.

Are these sorts of avalanches likely to happen in other parts of the world?
Honestly, I have no clue at the moment, but we would be much less surprised next time. We know now that this type of collapse can happen under special circumstances. (It happened once before in the Caucasus at Kolka Glacier.) One thing that should be investigated is whether there are other glaciersespecially polythermal oneswith these very fine-grained materials underneath them.

Three dimensional CNES Pléiades image of the avalanches. Processed by Etienne Berthier. Via Twitter.

Explorer 1: The Beginning of American Space Science

January 24th, 2018 by Preston Dyches

This article was published by NASA’s Jet Propulsion Laboratory on January 23, 2018. NASA is beginning several months of commemoration of the beginning of the Space Age and the evolution of Earth science from space.

Sixty years ago next week, the hopes of Cold War America soared into the night sky as a rocket lofted skyward above Cape Canaveral, a soon-to-be-famous barrier island off the Florida coast.

The date was Jan. 31, 1958. NASA had yet to be formed, and the honor of this first flight belonged to the U.S. Army. The rocket’s sole payload was a javelin-shaped satellite built by the Jet Propulsion Laboratory in Pasadena, California. Explorer 1, as it would soon come to be called, was America’s first satellite.

“The launch of Explorer 1 marked the beginning of U.S. spaceflight, as well as the scientific exploration of space, which led to a series of bold missions that have opened humanity’s eyes to new wonders of the solar system,” said Michael Watkins, current director of JPL. “It was a watershed moment for the nation that also defined who we are at JPL.”

In the mid-1950s, both the United States and the Soviet Union were proceeding toward the capability to put a spacecraft in orbit. Yet great uncertainty hung over the pursuit. As the Cold War between the two countries deepened, it had not yet been determined whether the sovereignty of a nation’s borders extended upward into space. Accordingly, then-President Eisenhower sought to ensure that the first American satellites were not perceived to be military or national security assets.

In 1954, an international council of scientists called for artificial satellites to be orbited as part of a worldwide science program called the International Geophysical Year (IGY), set to take place from July 1957 to December 1958. Both the American and Soviet governments seized on the idea, announcing they would launch spacecraft as part of the effort. Soon, a competition began between the Army, Air Force and Navy to develop a U.S. satellite and launch vehicle capable of reaching orbit.

At that time, JPL, which was part of the California Institute of Technology in Pasadena, primarily performed defense work for the Army. (The “jet” in JPL’s name traces back to rocket motors used to provide “jet assisted” takeoff for Army planes during World War II.) In 1954, the laboratory’s engineers began working with the Army Ballistic Missile Agency in Alabama on a project called “Orbiter.” The Army team included Wernher von Braun (who would later design NASA’s Saturn V rocket) and his team of engineers. Their work centered around the Redstone Jupiter-C rocket, which was derived from the V-2 missile Germany had used against Britain during the war.

JPL’s role was to prepare the three upper stages for the launch vehicle, which included the satellite itself. These used solid rocket motors the laboratory had developed for the Army’s Sergeant guided missile. JPL would also be responsible for receiving and transmitting the orbiting spacecraft’s communications. In addition to JPL’s involvement in the Orbiter program, the laboratory’s then-director, William Pickering, chaired the science committee on satellite tracking for the U.S. launch effort overall.

The Navy’s entry, called Vanguard, had a competitive edge in that it was not derived from a ballistic missile program — its rocket was designed, from the ground up, for civilian scientific purposes. The Army’s Jupiter-C rocket had made its first successful suborbital flight in 1956, so Army commanders were confident they could be ready to launch a satellite fairly quickly. Nevertheless, the Navy’s program was chosen to launch a satellite for the IGY.

University of Iowa physicist James Van Allen, whose instrument proposal had been chosen for the Vanguard satellite, was concerned about development issues on the project. Thus, he made sure his scientific instrument payload — a cosmic ray detector — would fit either launch vehicle. Meanwhile, although their project was officially mothballed, JPL engineers used a pre-existing rocket casing to quietly build a flight-worthy satellite, just in case it might be needed.

The world changed on Oct. 4, 1957, when the Soviet Union launched a 23-inch (58-centimeter) metal sphere called Sputnik. With that singular event, the space age had begun. The launch resolved a key diplomatic uncertainty about the future of spaceflight, establishing the right to orbit above any territory on the globe. The Russians quickly followed up their first launch with a second Sputnik just a month later. Under pressure to mount a U.S. response, the Eisenhower administration decided a scheduled test flight of the Vanguard rocket, already being planned in support of the IGY, would fit the bill. But when the Vanguard rocket was, embarrassingly, destroyed during the launch attempt on Dec. 6, the administration turned to the Army’s program to save the country’s reputation as a technological leader.

Unbeknownst to JPL, von Braun and his team had also been developing their own satellite, but after some consideration, the Army decided that JPL would still provide the spacecraft. The result of that fateful decision was that JPL’s focus shifted permanently — from rockets to what sits on top of them.

The Army team had its orders to be ready for launch within 90 days. Thanks to its advance preparation, 84 days later, its satellite stood on the launch pad at Cape Canaveral Air Force Station in Florida.

The spacecraft was launched at 10:48 p.m. EST on Friday, Jan. 31, 1958. An hour and a half later, a JPL tracking station in California picked up its signal transmitted from orbit. In keeping with the desire to portray the launch as the fulfillment of the U.S. commitment under the International Geophysical Year, the announcement of its success was made early the next morning at the National Academy of Sciences in Washington, with Pickering, Van Allen and von Braun on hand to answer questions from the media.

Following the launch, the spacecraft was given its official name, Explorer 1. (In the following decades, nearly a hundred spacecraft would be given the designation “Explorer.”) The satellite continued to transmit data for about four months, until its batteries were exhausted, and it ceased operating on May 23, 1958.

Later that year, when the National Aeronautics and Space Administration (NASA) was established by Congress, Pickering and Caltech worked to shift JPL away from its defense work to become part of the new agency. JPL remains a division of Caltech, which manages the laboratory for NASA.

The beginnings of U.S. space exploration were not without setbacks — of the first five Explorer satellites, two failed to reach orbit. But the three that made it gave the world the first scientific discovery in space — the Van Allen radiation belts. These doughnut-shaped regions of high-energy particles, held in place by Earth’s magnetic field, may have been important in making Earth habitable for life. Explorer 1, with Van Allen’s cosmic ray detector on board, was the first to detect this phenomenon, which is still being studied today.

In advocating for a civilian space agency before Congress after the launch of Explorer 1, Pickering drew on Van Allen’s discovery, stating, “Dr. Van Allen has given us some completely new information about the radiation present in outer space….This is a rather dramatic example of a quite simple scientific experiment which was our first step out into space.”

Explorer 1 re-entered Earth’s atmosphere and burned up on March 31, 1970, after more than 58,000 orbits.

For more information about Explorer 1 and the 60 years of U.S. space exploration that have followed it, visit:

https://explorer1.jpl.nasa.gov

January 2018 Puzzler

January 23rd, 2018 by Kathryn Hansen

Every month on Earth Matters, we offer a puzzling satellite image. The January 2018 puzzler is above. Your challenge is to use the comments section to tell us what we are looking at, when the image was acquired, and why the scene is interesting.

How to answer. You can use a few words or several paragraphs. You might simply tell us the location. 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 feature in the image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money or a trip to Mars, 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. After we post the answer, we will acknowledge the first person to correctly identify the image at the bottom of this blog post. We also may recognize readers who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have shaped the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you would like to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the past few months or if you work in geospatial imaging, please hold your answer for at least a day to give less experienced readers a chance to play.

Releasing Comments. Savvy readers have solved some puzzlers after a few minutes. To give more people a chance to play, we may wait between 24 to 48 hours before posting comments.

Good luck!

Why the SoCal Fires are So Fierce

December 7th, 2017 by Adam Voiland

NASA Earth Observatory image by Joshua Stevens, using MODIS data from LANCE/EOSDIS Rapid Response.

With thousands of homes threatened by intense wildfires burning in southern California, NASA Earth Observatory checked in with Jet Propulsion Laboratory scientist Natasha Stavros to learn more about the destructive blazes.

Earth Observatory (EO): Why have these fires been so fast-moving and destructive? Are fierce Santa Ana winds the key factor? Are anomalous temperatures, rainfall, ENSO conditions, bark beetle activity, or other factors playing an important role?

There are absolutely other factors. Santa Ana winds definitely played a role in spreading the fires, but the late fire season is a more complex story. Last year, we had a lot of heavy rains, and this increased fuel connectivity by enabling grasses and annual shrubs to flourish (hence the green hills last spring). However, we had a lot of record-breaking heat waves this year.

In fact, a recent study we conducted with NASA DEVELOP and the National Park Service in the Santa Monica Mountains showed that the number of days over 95 degrees Fahrenheit stressed established vegetation and contributed to massive die-off. Even though the drought is over, the trees are still recovering from the stress of reduced water availability for such an extended period. They are in a fragile state and their defenses are down. This means that they are even more susceptible to infestation, mortality, and ultimately fire danger.

EO: We have published MODIS (top of the page), Sentinel-2 (below), and nighttime VIIRS (bottom of the page) satellite imagery of these fires. Is there anything that you find particularly interesting or notable about these images?

To me, the noteworthy thing is that the plume is going over the ocean and not the continental United States (as we saw earlier this year). This has to do with the Santa Ana winds coming from the desert and pushing particulates, ozone, carbon monoxide, and other toxic pollutants away from where people live.

NASA Earth Observatory image by Joshua Stevens, using modified Copernicus Sentinel data (2017) processed by the European Space Agency.

As for the Sentinel-2 image, this is a great shot in that it really shows the value of remote sensing in monitoring fire. Flames that look like that are tens of meters tall. The flame length is proportional to the heat released from the flame, so these fires are very hot. Just like you would not want to stand too close to a bonfire with flames tens of meters tall, fire management does not want to put personnel in the path of those flames.

Images like these and fire behavior models help inform how we think the fire will move across the landscape. There is still a lot we do not know; our models are based on what we do know, so as fires become more intense, the models do not work as well, so this is an area of active research.

NASA Earth Observatory images by Joshua Stevens using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership.

EO: Is there anything to say about how these fires fit into longer term trends and/or changing climate patterns?

Fire regimes are changing. There is no question about that, and there are a lot of things contributing to it: climate change, a century of fire exclusion, and a growing wildland urban interface (WUI). As we move into the future, we expect there to be an increase in very large fire events. Also, and this is relevant for the events happening now, there will be longer fire seasons. Also, note that many of the fires that ignite close to where people live are actually caused by people. This is particularly true in Southern California.

As we move forward, we need to think about how to support smart fire management practices. By that I mean: what can we proactively do to reduce fire risk (i.e. the threat to valuable resources)?

Most fires on the coasts are lit by people. NASA Earth Observatory map by Joshua Stevens, using fire data courtesy of Balch, J. et al. (2017).

EO: What about JPL’s response to these fires? I was intrigued by the megafire project described here. Will your group be responding to this fire in any way?

We just received approval from NASA Headquarters to fly the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) over these fires. This sensor has been useful for investigating fuel load type and subsequent effects on emission types, fire behavior, and post-fire analysis (e.g., safety, erosion, area burned, fire severity or the amount of environmental change caused the fire, etc.) and is often analyzed in interagency and federal-academic coordination to improve our understanding of fire.

Another effort to support fire management includes work being done from JPL in coordination with the National Interagency Fire Center (NIFC) to help them develop metrics of fire danger using NASA satellites that provide hydrologic variables (e.g., soil moisture and vapor pressure deficit—the difference between the amount of moisture in the air vs how much it can hold). These metrics have a one-month forecast to help allocate fire management resources nationally, which is particularly important as our fire seasons extend throughout the year in multiple places at the same time.

Natasha Stavros. Image courtesy of N. Stavros.

Ground to Space: Iguazú Falls

November 29th, 2017 by Kathryn Hansen

In 2016, we published space-based imagery of Iguazú Falls—South America’s famous system of waterfalls, which is near a bend in the Iguazú River between Argentina and Brazil. Spray from the falls reaches so high that it is visible from space. A crew member aboard the International Space Station captured the photograph above on May 24, 2016.

The view from the ground is also quite compelling, attracting more than a million visitors per year. The images below show ground-based views of the falls, photographed photographed by NASA’s Alexey Chibisov from the Argentine side of the river on November 28, 2017. Chibisov took the photos while on vacation after weeks in the field with the Operation IceBridge mission.

Photo by Alexey Chibisov.

Lush, subtropical rainforest surrounds the falls. The vegetation here is part of a remaining fragment of the Atlantic Forest, which stretches from the east coast of South America inland toward the Amazon. The forest is habitat for tens of thousands of plant species and thousands of animal species.

Photo by Alexey Chibisov.

Sediment carried by the fast-moving river can impart a red-brown color to the water, especially after periods of heavy rain.

Photo by Alexey Chibisov.

The mist is the result of water that plunges as much as 260 feet (80 meters) over layers of basalt cliffs.

November 2017 Puzzler

November 28th, 2017 by Mike Carlowicz

Every month on Earth Matters, we offer a puzzling satellite image. The November 2017 puzzler is above. Your challenge is to use the comments section to tell us what we are looking at, when the image was acquired, and why the scene is interesting.

How to answer. You can use a few words or several paragraphs. You might simply tell us the location. 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 feature in the image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money or a trip to Mars, 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. After we post the answer, we will acknowledge the first person to correctly identify the image at the bottom of this blog post. We also may recognize readers who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have shaped the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you would like to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the past few months or if you work in geospatial imaging, please hold your answer for at least a day to give less experienced readers a chance to play.

Releasing Comments. Savvy readers have solved some puzzlers after a few minutes. To give more people a chance to play, we may wait between 24 to 48 hours before posting comments.

Good luck!

What A Wonderful World: Pinacate Peaks

November 10th, 2017 by Jesse Allen

In this satellite image, the prominent Pinacate Peaks stick out above the sand dune landscape of the Gran Desierto de Altar in Mexico’s Sonoran Province. The peaks are located just south of the Mexico-United States border. The Gran Desierto de Altar is one section of the broader Soronan Desert which covers much of northwestern Mexico and reaches into Arizona and California.

Steady, consistent winds in the area have shifted low-lying sand into dune fields in intriguing regular patterns. These same patterns of sand dune fields appear around the world in desert areas.

The volcanic peaks and cinder cones are believed to have formed from volcanic activity that first started roughly 4 million years ago — most likely due to the plate tectonics that also formed the Gulf of California around the same time. The most recent activity was perhaps 11,000 years ago. During the late 1960s, NASA trained astronauts in field geology at a number of sites around the world, including Pinacate Peaks, as preparation for the lunar landings.

The natural color image here is from the Landsat 8 satellite using its Operational Line Imager (OLI) instrument. The image was acquired on October 3, 2017. The volcanic cinder cone field stains the landscape of bright sand and tall dunes in the El Pinacate y Gran Desierto de Altar Biosphere Reserve.

 

NOTE: In a previous version of this post, I featured the EO-1 ALI image below, and an astute reader pointed out that these peaks, while in the Biosphere Reserve, are not Pinacate Peaks, but rather the Sierra de Rosario range nearby. I am geographically and tectonically embarassed…

The natural color image here is from the now-defunct Earth Observing 1 (EO-1) satellite using its Advanced Land Imager (ALI). The image was acquired on December 16, 2012. This late-year scene was just days before the solstice (the farthest south the Sun appears in the sky), so the tallest sand dunes and the volcanic peaks cast unusually long shadows across the ground.

EO-1 was launched in November 2000 as an engineering testbed for new sensor technology; in particular, the ALI instrument was a predecessor for the Landsat 8 Operational Land Imager. The EO-1 mission was so successful that it was extended past its original 18-month mission, and was only recently retired after 17 years of operation.

This post is republished from the Landsat science team page

In the giddy, early days following the flawless launch of Landsat 8, as the satellite commissioning was taking place, the calibration team noticed something strange. Light and dark stripes were showing up in images acquired by the satellite’s Thermal Infrared Sensor (TIRS).

Comparing coincident data collected by Landsat 8 and Landsat 7 — acquired as Landsat 8 flew under Landsat 7, on its way to its final orbit — showed that thermal data collected by Landsat 8 was off by several degrees.

This was a big deal. The TIRS sensor had been added to the Landsat 8 payload specifically because it had been deemed essential to a number of applications, especially water management in the U.S’s arid western states.

The TIRS error source was a mystery. The prelaunch TIRS testing in the lab had shown highly accurate data (to within 1 degree K); and on-orbit internal calibration measurements (measurements taken of an onboard light source with a known temperature) were just as good as they had been in the lab. But when TIRS radiance measurements were compared to ground-based measurements, errors were undeniably present. Everywhere TIRS was reporting temperatures that were warmer than they should have been, with the error at its worst in regions with extreme temperatures like Antarctica.

After a year-long investigation, the TIRS team found the problem. Stray light from outside the TIRS field-of-view was contaminating the image. The stray light was adding signal to the TIRS images that should not have been there—a “ghost signal” had been found.

The Ghostly Culprit

Scans of the Moon, together with ray tracing models created with a spare telescope by the TIRS instrument team, identified the stray light culprit. A metal alloy retaining ring mounted just above the third lens of the four-lens refractive TIRS telescope was bouncing out-of-field reflections onto the TIRS focal plane. The ghost-maker had been found.

Getting the Ghost Out—Landsat Exorcists in Action

With the source of the TIRS ghosts discovered, Matthew Montanaro and Aaron Gerace, two thermal imaging experts from the Rochester Institute of Technology, were tasked with getting rid of them.

Montanaro and Gerace had to first figure out how much energy or “noise” the ghost signals were adding to the TIRS measurements. To do this, a stray light optical model was created using reverse ray traces for each TIRS detector. This essentially gave Montanaro and Gerace a “map” of ghost signals. Because TIRS has 1,920 detectors, each in a slightly different position, it wasn’t just one ghost signal they had to deal with— it was a gaggle of ghost signals.

To calculate the ghost signal contamination for each detector, they compared TIRS radiance data to a known “correct” top-of-atmosphere radiance value (specifically, MODIS radiance measurements made during the Landsat 8 / Terra underflight period in March 2013).

Comparing the MODIS and TIRS measurements showed how much energy the ghost signal was adding to the TIRS radiance measurements. These actual ghost signal values were then compared to the model-based ghost signal values that Montanaro and Gerace had calculated using their stray light maps and out-of-field radiance values from TIRS interval data (data collected just above and below a given scene along the Landsat 8 orbital track).

Using the relationships established by these comparisons, Montanaro and Gerace came up with generic equations that could be used to calculate the ghost signal for each TIRS detector.

Once the ghost signal value is calculated for each pixel, that value can be subtracted from the measured radiance to get a stray-light corrected radiance, i.e. an accurate radiance. This algorithm has become known as the “TIRS-on-TIRS” correction. After performing this correction, the absolute error can be reduced from roughly 9 K to 1 K and the image banding, that visible vestige of the ghost signal, largely disappears.

“The stray light issue is very complex and it took years of investigation to determine a suitable solution,” Montanaro said.

This work paid off. Their correction—hailed as “innovative” by the Landsat 8 Project Scientist, Jim Irons—has withstood the scrutiny of the Landsat Science Team. And Montanaro and Gerace’s “exorcism” has now placed the Landsat 8 thermal bands in-line with the accuracy of the previous (ghost-free) Landsat thermal instruments.

USGS EROS has now implemented the software fix developed by these “Landsat Ghostbusters” as part of the Landsat Collection 1 data product. Savvy programmers at USGS, led by Tim Beckmann, made it possible to turn the complex de-ghosting calculations into a computationally reasonable fix that can be done for the 700+ scenes collected by Landsat 8 each day.

“EROS was able to streamline the process so that although there are many calculations, the overall additional processing time is negligible for each Landsat scene,” Montanaro explained.

A Ghost-Free Future

Gerace is now determining if an atmospheric correction based on measurements made by the two TIRS bands, a technique known as a split window atmospheric correction, can be developed with the corrected TIRS data.

Meanwhile, Montanaro has been asked to support the instrument team building the Thermal Infrared Sensor 2 that will fly on Landsat 9. A hardware fix for TIRS-2 is planned. Baffles will be placed within the telescope to block the stray light that haunted the Landsat 8 TIRS.

The Landsat future is looking ghost-free.

Related Reading:
+ RIT University News
+
TIRS Stray Light Correction Implemented in Collection 1 Processing, USGS Landsat Headline
+ Landsat Level-1 Collection 1 Processing, USGS Landsat Update Vol. 11 Issue 1 2017
+ Landsat Data Users Handbook, Appendix A – Known Issues

References:
Montanaro, M., Gerace, A., Lunsford, A., & Reuter, D. (2014). Stray light artifacts in imagery from the Landsat 8 Thermal Infrared Sensor. Remote Sensing, 6(11), 10435-10456. doi:10.3390/rs61110435

Montanaro, M., Gerace, A., & Rohrbach, S. (2015). Toward an operational stray light correction for the Landsat 8 Thermal Infrared Sensor. Applied Optics, 54(13), 3963-3978. doi: 10.1364/AO.54.003963 (https://www.osapublishing.org/ao/abstract.cfm?uri=ao-54-13-3963)

Barsi JA, Schott JR, Hook SJ, Raqueno NG, Markham BL, Radocinski RG. (2014) Landsat-8 Thermal Infrared Sensor (TIRS) Vicarious Radiometric Calibration. Remote Sensing, 6(11), 11607-11626.

Montanaro, M., Levy, R., & Markham, B. (2014). On-orbit radiometric performance of the Landsat 8 Thermal Infrared Sensor. Remote Sensing, 6(12), 11753-11769. doi: 10.3390/rs61211753

Gerace, A., & Montanaro, M. (2017). Derivation and validation of the stray light correction algorithm for the Thermal Infrared Sensor onboard Landsat 8. Remote Sensing of Environment, 191, 246-257. doi: 10.1016/j.rse.2017.01.029

Gerace, A. D., Montanaro, M., Connal, R. (2017). Leveraging intercalibration techniques to support stray-light removal from Landsat 8 Thermal Infrared Sensor data. Journal of Applied Remote Sensing, Accepted for Publication.