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jueves, 10 de mayo de 2018

Fundamental equations guide marine robots to optimal sampling sites

Observing the world’s oceans is increasingly a mission assigned to autonomous underwater vehicles (AUVs) — marine robots that are designed to drift, drive, or glide through the ocean without any real-time input from human operators. Critical questions that AUVs can help to answer are where, when, and what to sample for the most informative data, and how to optimally reach sampling locations.

MIT engineers have now developed systems of mathematical equations that forecast the most informative data to collect for a given observing mission, and the best way to reach the sampling sites.

With their method, the researchers can predict the degree to which one variable, such as the speed of ocean currents at a certain location, reveals information about some other variable, such as temperature at some other location — a quantity called “mutual information.” If the degree of mutual information between two variables is high, an AUV can be programmed to go to certain locations to measure one variable, to gain information about the other.  

The team used their equations and an ocean model they developed, called  Multidisciplinary Simulation, Estimation, and Assimilation Systems (MSEAS), in sea experiments to successfully forecast fields of mutual information and guide actual AUVs.

“Not all data are equal,” says Arkopal Dutt, a graduate student in MIT’s Department of Mechanical Engineering. “Our criteria … allow the autonomous machines to pinpoint sensor locations and sampling times where the most informative measurements can be made.”

To determine how to safely and efficiently reach ideal sampling destinations, the researchers developed a way to help AUVs use the uncertain ocean’s activity, by forecasting out a “reachability front” — a dynamic three-dimensional region of the ocean that an AUV would be guaranteed to reach within a certain time, given the AUV’s power constraints and the ocean’s currents. The team’s method enables a vehicle to surf currents that would bring it closer to its destination, and avoid those that would throw it off track.

When the researchers compared their reachability forecasts with the routes of actual AUVs observing a region of the Arabian Sea, they found their predictions matched where the vehicles were able to navigate, over long periods of time.

Ultimately, the team’s methods should help vehicles explore the ocean in an intelligent, energy-efficient manner.

“Autonomous marine robots are our scouts, braving the rough seas to collect data for us,” says mechanical engineering graduate student Deepak Subramani. “Our math equations help the scouts reach the desired locations and reduce their energy usage by intelligently using the ocean currents.”

The researchers, led by Pierre Lermusiaux, professor of mechanical engineering and ocean science and engineering at MIT, have laid out their results in a paper soon to appear in a volume of the book series, “The Sea,” published by the Journal of Marine Research.

In addition to Dutt and Subramani, Lermusiaux’s team includes Jing Lin, Chinmay Kulkarni, Abhinav Gupta, Tapovan Lolla, Patrick Haley, Wael Hajj Ali, Chris Mirabito, and Sudip Jana, all from the Department of Mechanical Engineering.

Quest for the most informative data

To validate their approach, the researchers showed that they could successfully predict the measurements that were the most informative for a varied set of goals. For example, they forecast the observations that were optimal for testing scientific hypotheses, learning if the ocean model equations themselves are correct or not, estimating parameters of marine ecosystems, and detecting the presence of coherent structures in the ocean. They confirmed that their optimal observations were 50 to 150 percent more informative than an average observation.

To reach the optimal observing locations, AUVs must navigate through the ocean. Traditionally, planning paths for robots has been done in relatively static environments. But planning through the ocean is a different story, as strong currents and eddies can constantly change, be uncertain, and push a vehicle off its preplanned course.

The MIT team thus developed path-planning algorithms from fundamental principles with the ocean in mind. They modified an existing equation, known as the Hamilton-Jacobi equation, to determine an AUV’s reachability front, or the furthest perimeter a vehicle is guaranteed to reach in a given amount of time. The equation is based on three main variables: time, a vehicle’s specific propulsion constraints, and advection, or the transport by the dynamic ocean currents — a variable which the group predicts by using its MSEAS ocean model.

With the new system, the AUVs can map out the feasible most informative paths and adapt their sampling plans as the uncertain ocean’s currents shift over time. In a first large, open-ocean test, the team calculated probabilistic reachability fronts and the most informative paths for autonomous floats and gliders in the Indian Ocean, as part of the Northern Arabian Sea Circulation-autonomous research (NASCar) initiative of the Office of Naval Research (ONR).

Over several months, the researchers, working out of their MIT offices, provided daily reachability forecasts to the ONR team to help guide the underwater vehicles, collecting optimal observations along the way.

“It was basically not much sleeping,” Lermusiaux recalls. “The forecasts were three to seven days out, and we would assimilate data and update every day. We did quite well. On average, the gliders and floats ended up where desired and within the probabilistic areas that we predicted.”

A moment of truth pays off

Lermusiaux and his colleagues also utilized their systems to plan “time-optimal paths” — trajectories that would get an AUV to a certain location in the shortest amount of time, given the forecast ocean current conditions.

With colleagues from the MIT Lincoln Laboratory and Woods Hole Oceanographic Institution, they tested these time-optimal paths in real time by holding “races” between identical propelled AUVs, off the coast of Martha’s Vineyard. In each race, one AUV’s course was determined by the team’s time-optimal path, while another AUV followed a path with the shortest distance to the same destination.

“It was tense — who will win?” Subramani recalls. “This was the moment of truth for us, after all those years of theoretical development with math equations and proofs.”

The team’s work paid off. In every race, the AUV operating under the team’s forecast reached its destination first, performing about 15 percent faster than the competing AUV. The team’s forecast helped the winning AUV to avoid strong currents that at times acted to block the other AUV.

“It was amazing,” Kulkarni says. “Even though physically the two paths were only less than a mile apart, following our predictions gave up to a 15 percent reduction in travel times. It shows our paths are truly time optimal.”

Among other applications, Lermusiaux, as a member of MIT’s Tata Center for Technology and Design, will be applying his ocean forecasting methods to help guide observations off the coast of India, where the vehicles will be tasked with monitoring fisheries to provide a potentially low-cost management system.

“AUVs are not very fast, and their autonomy is not infinite, so you really have to take into account the currents and their uncertainties, and model things rigorously,” Lermusiaux says. “Machine intelligence for these autonomous systems comes from rigorously deriving and merging governing differential equations and principles with control theory, information theory, and machine learning.”

This research was funded, in part, by the Office of Naval Research, the MIT Lincoln Laboratory, the MIT Tata Center, and the National Science Foundation.



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martes, 10 de abril de 2018

Understanding microbial competition for nitrogen

Nitrogen is a hot commodity in the surface ocean. Primary producers including phytoplankton and other microorganisms consume and transform it into organic molecules to build biomass, while others transform inorganic forms to access their chemical store of energy. All of these steps are part of the complex nitrogen cycle of the upper water column.

About 200 meters down, just below the ocean’s sunlit zone, resides a layer of nitrite, an intermediate compound in the nitrogen cycle. Scientists have found this robust feature, called the primary nitrite maximum, throughout the world’s oxygenated oceans. While several individual hypotheses have been put forward, none have convincingly explained this marine signature until now.

A recent Nature Communications study led by researchers in the Program in Atmospheres, Oceans and Climate (PAOC) within MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS) uses theory, modeling, and observational data to investigate the ecological mechanisms producing the observed nitrite accumulation and dictating its location in the water column. Lead author Emily Zakem — a former EAPS graduate student who is now a postdoc at the University of Southern California — along with EAPS Principal Research Scientist Stephanie Dutkiewicz and Professor Mick Follows show that physiological constraints and resource competition between phytoplankton and nitrifying microorganisms in the sunlit layer can yield this ocean trait. 

Regulating the biological pump

Despite its low oceanic concentration, nitrite (NO2-) plays a key role in global carbon and nitrogen cycles. Most of the nitrogen in the ocean resides in the inorganic form of nitrate (NO3-), which primary producers and microorganisms chemically reduce it to build organic molecules. Remineralization occurs when the reverse process takes place: Phytoplankton and other heterotrophic bacteria break down these organic compounds into into ammonium (NH4+), a form of inorganic nitrogen. Ammonium then can be consumed again by primary producers, which get their energy from light. Other microorganisms called chemoautotrophs also use the ammonium both to make new biomass and as a source of energy. To do this, they extract oxygen from seawater transform it, a process called nitrification, which occurs in two steps. First, the microbes convert ammonium into nitrite and then to nitrate.

Somewhere along the line, nitrite has been accumulating at the base of the sunlit zone, which has implications for ocean biogeochemistry. “Broadly, we’re trying to understand what controls the remineralization of organic matter in the ocean. It’s that remineralization that is responsible for forming the biological pump, which is the extra storage of carbon in the ocean due to biological activity,” says Zakem. It’s this strong influence that nitrogen has on the global carbon cycle that captures Follows’ interest. “Growth of phytoplankton on nitrate is called ‘new production’ and that balances the amount that’s sinking out of the surface and controls how much carbon is stored in the ocean. Growth of phytoplankton on ammonium is called recycled production, which does not increase ocean carbon storage,” Follows says. “So we wish to understand what controls the rates of supply and relative consumption of these different nitrogen species.”

Battle for nitrogen 

The primary nitrite maximum resides between two groups of microorganisms in most of the world’s oceans. Above it in the sunlit zone are the phytoplankton, and in the primary nitrite maximum and slightly below that rest an abundance of nitrifying microbes in an area with high rates of nitrification. Researchers classify these microbes into two groups based on their preferred nitrogen source: the ammonium oxidizing organisms (AOO) and nitrite oxidizing organisms (NOO). In high latitudes like the Earth’s subpolar regions, nitrite accumulates in the surface sunlit zone as well as deeper.

Scientists have postulated that there might be two not mutually exclusive reasons for the build-up of nitrite: Nitrification by chemoautotrophic microbes, and when stressed, phytoplankton can reduce nitrate to nitrite. Since isotopic evidence does not support the latter, the group looked into the former. 

“The long-standing hypothesis was that the locations of nitrification were controlled by the inhibition of light of these [nitrifying] microorganisms, so the microorganisms that carry out this process were restricted from the surface,” Zakem says, implying that these nitrifying chemoautotrophs got sunburned. But instead of assuming that was true, the group examined the ecological interactions among these and other organisms in the surface ocean, letting the dynamics fall out naturally. To do this they collected microbial samples from the subtropical North Pacific and evaluated them for metabolism rates, efficiencies and abundances, and assessed the physiological needs and constraints of the different nitrifying microbes by reducing the biological complexity of their metabolisms down to its underlying chemistry and thus hypothesizing some of the more fundamental constrains. They used this information to inform the dynamics of the nitrifying microbes in both a one-dimensional and three-dimensional biogeochemical models.

The group found that by employing this framework, they could resolve the interactions between these nitrifying chemoautotrophs and phytoplankton and therefore simulate the accumulation of nitrite at the primary nitrite maximum in the appropriate locations. In the surface ocean when inorganic nitrogen is a limiting factor, phytoplankton and ammonium oxidizing microbes have similar abilities to acquire ammonium, but because phytoplankton need less nitrogen to grow and have a faster growth rate, they are able to outcompete the nitrifiers, excluding them from the sunlit zone. In this way, they were able to provide an ecological explanation for where nitrification happens without having to rely on light inhibition dictating the location.

Comparing the fundamental physiologies of the nitrifiers revealed that differences in metabolisms and cell size could account for the nitrite build-up. The researchers found that the second step of the nitrification process that’s carried out by the nitrite oxidizers requires more nitrogen for the same amount of biomass being created by these organisms, meaning that the ammonia oxidizers can do more with less, and that there are fewer nitrite oxidizers than the ammonia oxidizers. The nitrite oxidizing microbes also have a higher surface to volume constraint than the smaller and ubiquitous ammonium oxidizing microbes, making nitrogen uptake more difficult. “This is an alternative explanation for why nitrite should accumulate,” Zakem says. “We have two reasons that point in the same direction. We can’t distinguish which one it is, but all of the observations are consistent with either of these two or some combination of both being the control.”

The researchers were also able use a global climate model to reproduce an accumulation of nitrite in the sunlit zone of places like subpolar regions, where phytoplankton are limited by another resource other than nitrogen like light or iron. Here, nitrifiers can co-exist with phytoplankton since the phytoplankton since there’s there’s more nitrogen available to them. Additionally, the deep mixed layer in the water can draw resources away from the phytoplankton, giving the nitrifiers a better chance at survival in the surface.

“There’s this long standing hypothesis that the nitrifiers were inhibited by light and that’s why they only exist at the subsurface,” Zakem says. “We’re saying that maybe we have a more fundamental explanation: that this light inhibition does exist because we’ve observed it, but that’s a consequence of long-term exclusion from the surface.”

Thinking bigger

“This study pulled together theory, numerical simulations, and observations to tease apart and provide a simple quantitative and mechanistic description for some phenomena that were mysterious in the ocean,” Follows says. “That helps us tease apart the nitrogen cycle, which has an impact on the carbon cycle. It's also opened up the box for using these kind of tools to address other questions in the microbial oceanography.” He notes that the fact that these microbes are shunting ammonium into nitrate near the sunlit zone complicates the story of carbon storage in the ocean.

Two researchers who were not involved with the study, Karen Casciotti, associate professor in the Stanford University Department of Earth System Science, and Angela Landolfi, a scientist in the marine biogeochemical modeling department at the GEOMAR Helmholtz Centre for Ocean Research Kiel, agree. “This study is of great significance as it provides evidence of how organisms’ individual traits affect competitive interactions among microbial populations and provide a direct control on nutrients' distribution in the ocean,” says Landolfi. “In essence Zakem et al., provide a better understanding of the link between different levels of complexity from individual- to community up to environmental level, providing a mechanistic framework to predict changes in community composition and their biogeochemical impact under climatic changes,” says Landolfi.

This research was funded by the Simons Foundation’s Simons Collaboration on Ocean Processes and Ecology, the Gordon and Betty Moore Foundation, and the National Science Foundation.



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miércoles, 21 de marzo de 2018

Soft robotic fish swims alongside real ones in coral reefs

This month scientists published rare footage of one of the Arctic’s most elusive sharks. The findings demonstrate that, even with many technological advances in recent years, it remains a challenging task to document marine life up close.

But MIT computer scientists believe they have a possible solution: using robots.

In a paper out today, a team from MIT’s Computer Science and Artificial Intelligence Laboratory (CSAIL) unveiled “SoFi,” a soft robotic fish that can independently swim alongside real fish in the ocean.

During test dives in the Rainbow Reef in Fiji, SoFi swam at depths of more than 50 feet for up to 40 minutes at once, nimbly handling currents and taking high-resolution photos and videos using (what else?) a fisheye lens.

Using its undulating tail and a unique ability to control its own buoyancy, SoFi can swim in a straight line, turn, or dive up or down. The team also used a waterproofed Super Nintendo controller and developed a custom acoustic communications system that enabled them to change SoFi’s speed and have it make specific moves and turns.

“To our knowledge, this is the first robotic fish that can swim untethered in three dimensions for extended periods of time,” says CSAIL PhD candidate Robert Katzschmann, lead author of the new journal article published today in Science Robotics. “We are excited about the possibility of being able to use a system like this to get closer to marine life than humans can get on their own.”

Katzschmann worked on the project and wrote the paper with CSAIL director Daniela Rus, graduate student Joseph DelPreto and former postdoc Robert MacCurdy, who is now an assistant professor at the University of Colorado at Boulder.

How it works

Existing autonomous underwater vehicles (AUVs) have traditionally been tethered to boats or powered by bulky and expensive propellers.

In contrast, SoFi has a much simpler and more lightweight setup, with a single camera, a motor, and the same lithium polymer battery that’s found in consumer smartphones. To make the robot swim, the motor pumps water into two balloon-like chambers in the fish’s tail that operate like a set of pistons in an engine. As one chamber expands, it bends and flexes to one side; when the actuators push water to the other channel, that one bends and flexes in the other direction.

These alternating actions create a side-to-side motion that mimics the movement of a real fish. By changing its flow patterns, the hydraulic system enables different tail maneuvers that result in a range of swimming speeds, with an average speed of about half a body length per second.

“The authors show a number of technical achievements in fabrication, powering, and water resistance that allow the robot to move underwater without a tether,” says Cecilia Laschi, a professor of biorobotics at the Sant'Anna School of Advanced Studies in Pisa, Italy. “A robot like this can help explore the reef more closely than current robots, both because it can get closer more safely for the reef and because it can be better accepted by the marine species.”

The entire back half of the fish is made of silicone rubber and flexible plastic, and several components are 3-D-printed, including the head, which holds all of the electronics. To reduce the chance of water leaking into the machinery, the team filled the head with a small amount of baby oil, since it’s a fluid that will not compress from pressure changes during dives.

Indeed, one of the team’s biggest challenges was to get SoFi to swim at different depths. The robot has two fins on its side that adjust the pitch of the fish for up and down diving. To adjust its position vertically, the robot has an adjustable weight compartment and a “buoyancy control unit” that can change its density by compressing and decompressing air.

Katzschmann says that the team developed SoFi with the goal of being as nondisruptive as possible in its environment, from the minimal noise of the motor to the ultrasonic emissions of the team’s communications system, which sends commands using wavelengths of 30 to 36 kilohertz.

“The robot is capable of close observations and interactions with marine life and appears to not be disturbing to real fish,” says Rus.

The project is part of a larger body of work at CSAIL focused on soft robots, which have the potential to be safer, sturdier, and more nimble than their hard-bodied counterparts. Soft robots are in many ways easier to control than rigid robots, since researchers don’t have to worry quite as much about having to avoid collisions.

“Collision avoidance often leads to inefficient motion, since the robot has to settle for a collision-free trajectory,” says Rus, the Andrew and Erna Viterbi Professor of Electrical Engineering and Computer Science at MIT. “In contrast, a soft robot is not just more likely to survive a collision, but could use it as information to inform a more efficient motion plan next time around.”

As next steps the team will be working on several improvements on SoFi. Katzschmann plans to increase the fish’s speed by improving the pump system and tweaking the design of its body and tail.

He says that they also plan to soon use the on-board camera to enable SoFi to automatically follow real fish, and to build additional SoFis for biologists to study how fish respond to different changes in their environment.

“We view SoFi as a first step toward developing almost an underwater observatory of sorts,” says Rus. “It has the potential to be a new type of tool for ocean exploration and to open up new avenues for uncovering the mysteries of marine life.”

This project was supported by the National Science Foundation.



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sábado, 17 de febrero de 2018

Stefan Helmreich conducts fieldwork aboard the unique FLIP ship

The author of the award-winning book “Alien Ocean: Anthropological Voyages in Microbial Seas,” MIT anthropologist Stefan Helmreich has a wealth of experience examining how scientists think about the world. And recently, he gained a new perspective — quite literally — by taking his research to the Floating Instrument Platform, known colloquially as the FLIP ship.

Operated by the Scripps Institution of Oceanography in La Jolla, California, the FLIP ship is a unique scientific vessel that can operate in either a horizontal or vertical position. “Everyday life on the ship has an M. C. Escher sort of feel, with doors, sinks, and stairs appearing in both vertical and horizontal alignments,” says Helmreich, who is the Elting E. Morison Professor of Anthropology and head of anthropology within the School of Humanities, Arts, and Social Sciences.

Helmreich boarded FLIP in October of 2017 to conduct anthropological fieldwork into contemporary ocean wave science — seeking to understand more about the changing theories, models, and technologies that physical oceanographers use to apprehend waves. While aboard ship, he conducted interviews and joined people in their everyday work to learn how they engage with and understand the surface of the sea.

 Waves are both a physical and cultural reality

“Wave science is a field with relevance to everything from weather and hurricane prediction, to surf forecasts, to coastal and ocean engineering, to operations research, to shipping, to climate change science, and more,” says Helmreich — whose book "Alien Ocean" drew praise from the journal Nature for capturing “the excitement and crucial nature of oceanographic research.”

In his current research, Helmreich emphasizes that waves are not only physical phenomena; they are entities that become scientifically legible through measurement, models, and theories — that is, through human cultural activity.

Within this framing, a range of questions become available, from “How have scientists come to think of ocean waves as populations and statistical processes?” to “How do mathematical conceptualizations of waves relate to the everyday vocabularies of seafarers, shipbuilders, and surfers?”

Aboard the FLIP ship

On FLIP, Helmreich had the opportunity to investigate such questions while getting to know a unique vessel. In its horizontal conformation, the FLIP travels like an ordinary oceangoing vessel. But by “flipping” 90 degrees into a vertical position once it arrives at its destination, it can become, essentially, a enormous spar buoy.

“In this position, the vessel looks like nothing so much as a floating metal treehouse,” says Helmreich. With most of the platform’s 108-meter length below the surface, scientists have the rare opportunity to work on the open ocean in a remarkably stable environment. FLIP has been a significant instrument in the long history of U.S.-based wave science, permitting scientists to investigate underwater acoustics, to capture the varied spectrum of ocean waves, and much else.

What did Helmreich learn on FLIP? Helmreich says that he became particularly fascinated by the work of oceanographers who were using novel laser technologies — operating in visible and invisible frequencies — to make precise measurements of ocean turbulence at the sea surface, where wind and waves interact in ways that are still not fully characterized.

The media of comprehension

What struck him — aside from the experience of doing fieldwork on a ship on which everything seemed sideways — was how wave scientists apprehend their data through cameras and computer screens that present frame-by-frame, color-coded visualizations of the wave field.

“This mode of understanding waves reminded me of the technology of cinema — even recalling to me an 1891 film called ‘La Vague,’ made by Étienne Jules Marey to study the movement of a wave in the Bay of Naples,” says Helmreich.

“In important ways, wave science is enabled by the media — photographic, computational, acoustic — that scientists employ to comprehend ocean wave generation, propagation, breaking, and more,” he adds.

Gravitational, cardiac, symbolic, and gendered

Back on land, Helmreich continues to extend his research on waves to a wide range of disparate phenomena that employ the same abstract concept. Drawing on media theory and sound studies, for example, he has lately asked, in an essay in Wire magazine, how we should understand the sounds of gravitational wave detection (a related article in Cultural Anthropology drew on interviews with MIT physicists Nergis Mavalvala, Scott Hughes, and David Kaiser), and in an article in Current Anthropology, how medical measures of cardiac waves have changed health care.

In a recent essay in Womens Studies Quarterly, a feminist studies journal, Helmreich also explores how ocean waves have been described with gendered symbolism in mythology, literature, and social theory. Here is an excerpt from his thought-provoking article, “Potential Energy and the Body Electric,” in Current Anthropology:

“An orienting note: waves are tricky to think about. Waves are not merely material processes of energy propagation or of vibration. They are also abstractions crafted by scientists who decide what will count as wave activity, whether in a passive medium (as with water waves, sound waves), an excitable medium (as with cardiac and brain waves), or in a vacuum (as with light waves or radio waves; Barad 2007). Literary critic Gillian Beer (1996) has examined the popular reception of wave theory in physics alongside early twentieth-century modernism, noting that both emphasized the transitory and illusory character of the apparently solid world (Beer points readers to the etheric ocean of wireless radio and to Virginia Woolf’s novel of fluid subjectivities ‘The Waves’). Beer suggests that the electromagnetic ‘wave enters the modernist world as a token of a self-conscious relativism about representational schemes. This doubleness is still with us today. Waves are at once processes as well as traces of those processes — traces inscribed in graphs or charts and, less obviously, in the very model of waves that is bound up with their observation.”

Story by MIT SHASS Communications
Editorial and Design Director: Emily Hiestand
Senior Writer: Kathryn O'Neil



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miércoles, 14 de febrero de 2018

Chaos and climate: Celebrating two pioneers of modern meteorology

Our understanding of atmospheric and climate dynamics, as well as weather prediction and its limits, would not be what it is today without advances in the fundamental science of modern meteorology that took place at MIT in the post WWII era. Much of this is thanks to two prominent MIT meteorologists born a hundred years ago, but whose work is very much relevant today.

Earlier this month, the Department of Earth, Atmospheric and Planetary Sciences (EAPS) celebrated the lives and scientific legacies of these two former MIT professors, Edward Norton Lorenz and Jule Gregory Charney, during a two-day symposium: MIT on Chaos and Climate. The event was organized by EAPS faculty from the Lorenz Center and the Program in Atmospheres, Oceans and Climate (PAOC), marking the centennial of the scientists’ birth.

The department brought together the MIT community and friends and welcomed back alumni, and former faculty and scientists from EAPS and the former Department of Meteorology (Course XIX). Also invited were respected colleagues from many scientific fields affected by the work of Charney and Lorenz, including oceanography, meteorology, physics, applied mathematics, and climate science. Together, the group composed of biological and professional families shared vignettes and personal testimonials of the scientists on the first day, and discussed the broader impacts that Charney and Lorenz’s research had on the department and the broader community on the second.

Meteorology’s origins at MIT

Charney and Lorenz were members and chairs of the former Department of Meteorology, which emerged from the country’s first meteorology program founded at MIT by Carl-Gustaf Rossby, considered one of the founders of modern meteorology. In 1983, the department merged with Course XII to become the current EAPS, and was the forefather of PAOC.

The pioneering work of Charney and Lorenz heralded the field of modern meteorology. “It’s fair to say that Jule Charney turned the mystery of the erratic behavior of the atmosphere into a recognizable, although a very, very difficult problem in fluid physics,” said Joe Pedlosky, Woods Hole Oceanographic Institution Emeritus Senior Scientist, on the symposium’s second day.

Charney’s quasi-geostrophic vorticity equations allowed for concise mathematical description of large-scale atmospheric and oceanic circulations, enabling the numerical weather prediction. Among this and his many fundamental contributions to the field, Charney identified “baroclinic instability,” the mechanism that explains the size, structure, and growth rate of mid-latitude weather systems, and is a ubiquitous phenomenon in rotating, stratified fluids like our oceans and atmosphere. His innovative research provided insights to the theories of weather systems, hydro-dynamical instability, atmospheric wave propagation, hurricanes, drought, desertification, atmospheric blocking, and ocean currents. Many felt the pull of his charisma and academic integrity, falling into “orbit around the Charney sun.” This, along with his idealism and quest for fascinating research results, was the driving force behind many national and international weather initiatives and programs.

“Being in the room with Charney was like being in the room with a tiger, a very friendly tiger,” said David Randall, University Distinguished Professor at Colorado State University.

Lorenz could be considered Charney’s department foil. Many described him as a quiet, humble soul, and in Charney’s words as remembered by Pedlosky, “Lorenz is a genius with a soul of an artist.”

He revolutionized our understanding of atmospheric dynamics and circulation through research into the energetics of stratified, rotating fluids. In “one of the greatest intellectual advances of our time,” Lorenz set out to show that statistical long-range weather forecasting did not perform as well as numerical forecasting, and in the process observed “deterministic chaos,” facts that were highlighted by talks from Kerry Emanuel, the MIT Cecil and Ida Green Professor of Atmospheric Science and co-director of the Lorenz Center, and Tim Palmer, the Royal Society Research Professor at the University of Oxford.

Lorenz’s meticulous research found that infinitesimal differences in initial conditions produced dramatically different forecasts. Chaos theory, popularized as the butterfly effect, shifted our thinking away from deterministic numerical weather prediction to more probabilistic forecasts. “History may well record that Ed Lorenz had hammered the last nail into the coffin of the Cartesian universe,” Emanuel said. Despite the fact that the results of Charney and Lorenz’s research were largely opposing, Palmer noted that their work is now seamlessly intertwined for the benefit of science and society.

Ripples in weather, climate, and beyond earth science

The symposium, through formal and informal presentations, painted a picture of what meteorology was like under the leadership of Lorenz and Charney, and their influence on other fields of study.

On the symposium’s first day, alumni, colleagues, friends, and family shared personal stories of encounters with Charney and Lorenz, including anecdotes about lesser known research and affiliations like Charney’s work with the Union of Concerned Scientists, the discovery of chaos and the jetstream, the study of storm surge in Venice, and MIT’s connection with meteorology in Italy. Mankin Mak, alum of Lorenz’s group and Professor Emeritus at the Department of Atmospheric Sciences at the University of Illinois, even named the “Charney number” after the scientist. All the while, the camaraderie between the Course XIX alumni and excitement to be back in EAPS was palpable, spilling over into the evening’s dinner and the following day.

The second part of the symposium opened to the public and focused on the influence of Lorenz and Charney’s research. This included talks on cloud aggregation, hydrology and atmospheric coupling leading to desertification, oceanography and a realistic model of the Gulf Stream, observation of the turbulent cascade in nonlinear systems, CO2-related climate change, chaos in our solar system, fluid dynamics of pathogen transmission, tipping points in population dynamics, and more.

First-day attendees experienced the extent of the researchers’ work through multimedia. While a slideshow of Lorenz and Charney played, EAPS graduate students Brian Green, Mukund Gupta, Megan Lickley and Santiago Benavides, as well as postdocs Ed Doddridge, Jon Lauderdale, Chris Follett, and Daniel Koll shared posters of their own research during the morning of the symposium’s first day. Two displays were unveiled, which would be hung outside the EAPS Charney Library, across from Charney’s old office on the 14th floor where this groundbreaking work took place, and on the 18th floor. Lab assistant Bill McKenna set up a replica of the LGP-30 computer and printer that Lorenz used for his renowned calculations and showed how it would have been used. Short films from Meg Rosenberg, a producer and editor at MIT Video Productions, and Josh Kastorf, from the Earth Resources Laboratory in EAPS, established timelines of Lorenz and Charney’s life and work at MIT, and explained the origins and implications of chaos theory, respectively.

Charney had once remarked that a “scientist’s interest in the history of his own field was the first sign of senility,” but Raffaele Ferrari, the EAPS Cecil and Ida Green Professor of Oceanography and chair of PAOC, believes that revisiting the past can provide valuable lessons for future thinking and research. “For the students, it must have been inspirational and helpful to see where this department comes from,” Ferrari says. “You realize [that] the history of this department is quite impressive … and the people were here that created this field. … There is no other department like that, definitely [not] in meteorology, that has ever achieved that kind of leadership intellectually on every level.”

By revisiting the group’s history, students could see the evolution of scientific ideas and the values that made the department what it was and that became part of its legacy. In a sentiment echoed by keynote speaker Ernest Moniz, the MIT Cecil and Ida Green Professor Emeritus of Physics and Engineering Systems and special advisor to the MIT President, basic research is the lifeblood of a successful society in the long-term. “[Lorenz and Charney were] thinking about the fundamentals of the problem with students here at MIT,” he said. This practice of fostering curiosity-driven research now underpins the mission of the Lorenz Center: to understand and predict global climate change. “And [that’s] always that you want — to fundamentally understand the problem and then as a result you can make an impact on the real world, on practical applications.”

EAPS professors Ferrari, Emanuel, John Marshall (event MC), Paola Rizzoli, and Dan Rothman organized the symposium. The event was sponsored by the Henry Houghton Fund and the Lorenz Center within EAPS.

Those interested in making a contribution to the Lorenz Center Fund, or to support the renovation of the Charney Library, can contact Angela Ellis at 617-253-5796 or via email: aellis@mit.edu.



from MIT News - Oceanography and ocean engineering http://ift.tt/2EmDg6f

viernes, 15 de diciembre de 2017

Unlocking marine mysteries with artificial intelligence

Each year the melting of the Charles River serves as a harbinger for warmer weather. Shortly thereafter is the return of budding trees, longer days, and flip-flops. For students of class 2.680 (Unmanned Marine Vehicle Autonomy, Sensing and Communications), the newly thawed river means it’s time to put months of hard work into practice.

Aquatic environments like the Charles present challenges for robots because of the severely limited communication capabilities. “In underwater marine robotics, there is a unique need for artificial intelligence — it’s crucial,” says MIT Professor Henrik Schmidt, the course’s co-instructor. “And that is what we focus on in this class.”

The class, which is offered during spring semester, is structured around the presence of ice on the Charles. While the river is covered by a thick sheet of ice in February and into March, students are taught to code and program a remotely-piloted marine vehicle for a given mission. Students program with MOOS-IvP, an autonomy software used widely for industry and naval applications.

“They’re not working with a toy,” says Schmidt’s co-instructor, Research Scientist Michael Benjamin. “We feel it’s important that they learn how to extend the software — write their own sensor processing models and AI behavior. And then we set them loose on the Charles.”

As the students learn basic programming and software skills, they also develop a deeper understanding of ocean engineering. “The way I look at it, we are trying to clone the oceanographer and put our understanding of how the ocean works into the robot,” Schmidt adds. This means students learn the specifics of ocean environments — studying topics like oceanography or underwater acoustics. 

Students develop code for several missions they will conduct on the Charles River by the end of the semester. These missions include finding hazardous objects in the water, receiving simulated temperature and acoustic data along the river, and communicating with other vehicles.

“We learned a lot about the applications of these robots and some of the challenges that are faced in developing for ocean environments,” says Alicia Cabrera-Mino ’17, who took the course last spring.

Augmenting robotic marine vehicles with artificial intelligence is useful in a number of fields. It can help researchers gather data on temperature changes in our ocean, inform strategies to reverse global warming, traverse the 95 percent of our oceans that has yet to be explored, map seabeds, and further our understanding of oceanography.

According to graduate student Gregory Nannig, a former navigator in the U.S. Navy, adding AI capabilities to marine vehicles could also help avoid navigational accidents. “I think that it can really enable better decision making,” Nannig explains. “Just like the advent of radar or going from celestial navigation to GPS, we’ll now have artificial intelligence systems that can monitor things humans can’t.”

Students in 2.680 use their newly acquired coding skills to build such systems. Come spring, armed with the software they’ve spent months working on and a better understanding of ocean environments, they enter the MIT Sailing Pavilion prepared to test their artificial intelligence coding skills on the recently melted Charles River.

As marine vehicles glide along the Charles, executing missions based on the coding students have spent the better part of a semester perfecting, the mood is often one of exhilaration. “I’ve had students have big emotions when they see a bit of AI that they’ve created,” Benjamin recalls. “I’ve seen people call their parents from the dock.”

For this artificial intelligence to be effective in the water, students need to combine software skills with ocean engineering expertise. Schmidt and Benjamin have structured 2.680 to ensure students have a working knowledge of these twin pillars of robotic marine vehicle autonomy.

By combining these two research areas in their own research, Schmidt and Benjamin hope to create underwater robots that can go places humans simply cannot. “There are a lot of applications for better understanding and exploring our ocean if we can do it smartly with robots,” Benjamin adds.



from MIT News - Oceanography and ocean engineering http://ift.tt/2jXnmaf

martes, 21 de noviembre de 2017

Pesca industrial sin control en África: el botín de las flotas extranjeras

Hoy es el Día Mundial de la Pesca, un día especialmente celebrado por los millones de mujeres y hombres altamente dependientes de esta actividad, y por eso ponemos la mirada en África occidental. Una...

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