Paleomagnetism and Problem-Solving | September 5, 2012

With each challenge it encountered, the more the team seemed to take on a life of its own, emerging as a dynamic, complex organism, much more than the sum of its parts. Facing another technical hurdle, it continued to push toward its goal of mapping the underground faults and fractures in Surprise Valley relying on each other’s ideas and expertise. It quickly adapted to the new challenge, shifting plans as necessary. While I learned more about how geophysicists collect magnetic data on the ground, SIERRA engineers engaged in an intense brainstorming process, culminating in a potential breakthrough.

Yesterday morning I followed lead scientists Jonathan Glen and Noah Athens, both from the U.S. Geological Survey, out to the field, planning to observe them as they communicated with SIERRA while driving four-wheel all-terrain vehicles (ATVs). Not long after they unloaded the ATVs, Jonathan received a call from the ground base station.  The crew had lost all signal from the UAS’ fluxgate magnetometer, which would allow them to correct for magnetic noise associated with the magnetization of the aircraft that could obscure signals arising from geologic structures they’re interested in mapping. After hanging up, Jonathan leapt back into his truck and sped off to Cedarville Airport to rejoin the team, leaving Noah and I to collect magnetic data by foot instead.

Lead scientist Jonathan Glen of the U.S. Geological Survey (USGS) drilling a basalt core in the Larkspur Hills

Lead scientist Jonathan Glen of the U.S. Geological Survey (USGS) drilling a basalt core in the Larkspur Hills

That afternoon, after Noah and I finished collecting magnetic data along the line the team had mapped, Jonathan picked us up in his truck, updating us on the crew’s troubleshooting session.  The ground crew was still huddled beneath the hangar, intently trying to pinpoint the source of the communication problems. They thought that the aircraft vibrations had weakened a cable connection that prevented the fluxgate from transmitting compensation data to the ground, he explained as he drove us to an outcrop in the Larkspur Hills along the eastern rim of the valley.

There, Jonathan planned to drill cores from a dark, porous rock called basalt, which forms when lava cools. The team wants to determine the magnetic properties of the basalt at the surface, since this information could help them map the geologic features buried in the basin. We can’t determine the structure of the subsurface from magnetic field data alone, since magnetic fields aren’t unique; an infinite number of different structures can generate the same field.

But the team can use the magnetic properties of the basalt on the outcrop to model the features below the valley, assuming that the same basalt can be found in both areas. As you might recall from a previous post, tectonic forces have faulted and extended the crust across most of the western U.S.  The result has been the development of a broad region of alternating basins and ranges. As magma broke through the crust in the Larkspur Hills millions of years ago, the lava flowed down to the valley below. Faulting continued and some of the basalt was buried under sediments in the valley, while some was uplifted and tilted and remains exposed at the surface.

The magnetic fields that leave their imprint on a rock over time collectively comprise the rock’s magnetization. Paleomagnetism parses this field into its composite parts. Assuming that the rocks on the outcrop are similar to those that are faulted and fractured below the basin, the team can feed the surface rocks’ magnetic properties into software they use to model the subsurface features. Each of the properties the researchers measure in their samples (i.e., density and magnetism) acts as a constraint, which helps to refine the model, so that it better represents the shape of the rocks in the subsurface.

Jonathan using an orienter to measure the spatial orientation of a basalt core

Jonathan using an orienter to measure the spatial orientation of a basalt core

Geophysicists know that they’ve come up with a reasonable model when it’s consistent with geologic evidence and when the magnetic and gravity fields their model generates closely match the measured fields. They feed measurements from the rock samples into modeling software. The screen displays the magnetic and gravity readings as curves with various anomalies.  The shape of these curves depends on the geometry and properties–that is, the density and magnetism–of the rocks in the subsurface. By constraining the density and magnetic properties of the model’s composite rock units to values within the range of the properties of the rocks they’ve sampled at the surface, the researchers are able to focus on determining the depth, shape, and extent of the rocks. Each value for these characteristics affects the curves’ spread and shape. Sometimes a value will improve the fit of one curve and not the other. When the model’s gravity and magnetic curves closely resemble the measured anomalies, then the geophysicists have produced a model that is consistent with the observed data.  Any additional constraints, for example from seismic data or drill cores, that can be incorporated into the model, helps to further improve the likelihood that it accurately represents the subsurface.

Close-up view of an orienter

Close-up view of an orienter

Geophysicists take paleomagnetic samples by drilling cores from rock using a modified chainsaw fitted with a cylindrical bit. Stopping at various rocks along the outcrop, Jonathan yanked hard on the pull cord, and drilled into the rock.

Jonathan and Noah then used an instrument, called an orienter, that will allows them to reconstruct the orientation of the core’s magnetization, measured in the lab, to its original orientation prior to sampling. With the core still embedded in the rock, Jonathan placed the orienter, into the hole he had just drilled and used it to measure the core’s angle (or azimuth) from North and its tilt with respect to the horizontal, which together uniquely define the core’s orientation in space. Jonathan then inserted a brass rod through a slot running lengthwise down the top of the orienter that left a brass mark on the core to indicate its top. Next he pulled out the orienter and extracted the core from the outcrop. He handed the core to Noah, who used a red felt-tip pen to draw marks to indicate the ends of the core that were on the inside and outside of the rock.  Noah then slipped the core into a drawstring pouch for analysis in the lab.

But to accurately determine the core’s azimuth with respect to North, the researchers can’t always rely on a compass measurement.  That’s because local magnetic sources can sometimes significantly deflect the compass needle.

To overcome this problem, scientists can use a solar compass to determine the core’s true angle from North. A long pin centered on the stage of the orienter casts a shadow across set of numbers encircling the edge of the instrument. The researchers record the angle of the shadow, which they then feed, along with the time, latitude, and longitude, into software that provides them with the solar azimuth, the angle of the sun from true north. From that value, they can obtain the true angle of the core with respect to North. The team also records the magnetic north azimuth, based just on a compass measurement, as a standard practice in case the sun isn’t visible. For example, the team might start orienting cores while the sun is still out, but by the time they reach the last few cores, the sky will have grown cloudy.

USGS researcher Noah Athens marking a basalt core’s spatial orientation within the rock from which it was drilled.

USGS researcher Noah Athens marking a basalt core’s spatial orientation within the rock from which it was drilled.

Jonathan knelt down before each rock he had drilled, taking measurements with the orienter and reading them off to Noah, who jotted them down in a pocket-sized notebook.  It looked like laborious work, kneeling on the stone-strewn ground and squinting into the orienter as he took care to make accurate readings, the back of his neck red and glistening in the heat. We finished orienting the last sample just before the sun began slowly dipping below the horizon.  After gathering our belongings, we drove back to the house, tired yet satisfied after a strenuous day of fieldwork.

At 10:30 that evening, one of the engineers for SIERRA’s scientific instrumentation, or payload, stopped by the house where the USGS team members were staying.  He spoke excitedly about the ground base station’s troubleshooting session that day.

SIERRA engineers had fashioned custom test equipment and assembled a ground station to help ensure accurate troubleshooting. Puzzlingly, the UAS had no problem transmitting, or telemetering, the fluxgate data while the aircraft was grounded. The payload systems engineers painstakingly probed the scientific instrumentation for loose cables that might be preventing transmission specifically of the fluxgate compensation data. Meanwhile, the other SIERRA engineers evaluated complementary systems, like the electronics. They performed a complete electrical system analysis, meticulously testing each connector’s communication with the ground station.

Hunched over the payload, the payload systems engineers sounded positive and earnest as they shared their hypothesis about the aircraft vibrations with the rest of the team, although they suspected that something else was to blame.  The others also sounded doubtful.  Just to make sure, they simulated the aircraft’s vibrations by running SIERRA’s motors at high revolutions per minute (rpm).  They didn’t observe any communication problems.

Why could SIERRA transmit compensation data from the ground but not from the air?  The payload systems engineers suggested that the team try flying SIERRA again after sealing the loose cables in place with silicone. Even if the vibrations weren’t causing the communication problems, maybe securing the cables would still somehow solve the actual problem, whatever that might be.

“Unless you find the problem, I am not going to send the aircraft back up,” SIERRA lead engineer Randy Berthold said firmly.

Having already lost precious flight time, the team began heatedly batting around ideas.  “Maybe the fluxgate just can’t transmit the data quick enough,” ventured SIERRA engineer Ric Kolyer.  Though he couldn’t specify a cause for the lag, the others sensed that he was leading them on the right track.

“I know what the problem is!” Geometrics engineer Misha Tchernychev exclaimed a few minutes later. Geometrics is the company that manufactured the cesium vapor magnetometer and the replacement fluxgate.  “It’s the baud rate.” Each instrument has a maximum rate of data transfer, or baud rate.  The highest maximum baud rate possible with the cesium vapor magnetometer is 10 samples per second, or 10 Hertz (Hz). When the engineers installed the new fluxgate, which could sample more frequently, they decided to set its baud rate to 50 Hz to maximize the data it would collect per unit of distance traveled.  But maybe the radio system they were using to telemetry the data to the ground station couldn’t handle such a high rate of data flow.

Ric came up with the analogy of pouring water through a funnel. The amount of water that can flow through a funnel is limited by the size of the funnel hole.  If water is poured through the funnel faster than the funnel can drain it, the funnel will overflow.  Likewise, the fluxgate was sending data to the radio faster than it could telemetry it to the ground station.  The data overflowed, failing to reach the ground station.

“Everyone realized immediately that Misha was correct,” said Jonathan.  “His diagnosis fit the symptom of the increasing loss of data…. It made perfect sense with the behavior of the instrument.”

The team reasoned that they didn’t have trouble communicating with SIERRA when it was grounded because they hadn’t allowed it to run long enough, leading them to trace the problem to flight vibrations. Using Ric’s analogy, water initially flows through a funnel, even when it’s poured too quickly. Only after the water is filled past the funnel does it start overflowing. Likewise, while SIERRA was aloft, the team initially saw magnetic data being transmitted via the radio link.  They didn’t begin losing data until several minutes later. To test this theory, the team planned to ramp up the fluxgate’s maximum baud rate to cause the instrument’s communication with the ground station to fail.  The fluxgate’s communication with the ground station should eventually fail, even with the aircraft landed.

The payload systems engineers and USGS researcher Geoff Phelps began steadily increasing the fluxgate’s data transfer rate. At the same time, the others continued a thorough test of the complementary systems. By then, dusk had already fallen.  “Power up,” the payload systems engineers said with each rate increase, Geoff repeating after them as they turned on the aircraft. “Power down,” they said in succession as they shut it down.  Though glassy-eyed and unshaven, they remained upbeat, feeling the solution just within grasp. As with the complementary systems, the other SIERRA engineers tested the communication of each of the fluxgate’s connectors with the ground.

At 10:00 that evening, convinced that they had definitively established the excessively high baud rate on the fluxgate as the problem, they dropped the maximum baud rate down to a manageable 10 Hz, enabling the instrument to sustain communication with the ground base station. Beaming, Randy agreed to let SIERRA fly again.

Tomorrow, the SIERRA will survey the north central detailed region and perimeter of Surprise Valley.  If all goes well, it may even have time to survey another southern detailed region the following day in addition to the broad survey across the entire valley that the USGS researchers had originally planned.  Though encouraged, the team members continue to hold their breaths.  Stay tuned to find out whether tomorrow finds them back at the hangar or out on the tarmac, watching SIERRA complete its last few surveys of the valley.

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Down and Dirty in the Field | September 4, 2012

Back in his cozy office lined with laden bookshelves and topographic maps, lead scientist Jonathan Glen spoke about the necessity of adaptability in fieldwork.  The suddenness with which conditions could change, despite the team’s careful planning, was a common thread running through the Surprise Valley expedition, first when the researchers encountered technical issues two days ago and again today.  But what was important was that the team pushed forward to fulfill their original purpose–“coming together to do great science,” as Jonathan had said–no matter what path they took.  After spending the first half of the field session at Cedarville Airport, watching SIERRA collect magnetic data from the sky, a sudden change in plans finally gave me the chance to soil my hiking boots as I learned about how geoscientists gather data on the ground.

U.S. Geological Survey (USGS) researcher Noah Athens on an all-terrain vehicle (ATV).

U.S. Geological Survey (USGS) researcher Noah Athens on an all-terrain vehicle (ATV).

On the third day of our expedition to map underground faults and fractures in Surprise Valley using unmanned aerial systems (UAS), the team felt confident that the SIERRA UAS would have a successful flight.  NASA engineers had just fitted SIERRA with a new fluxgate magnetometer, an instrument that allows them to correct for magnetic fields associated with the aircraft that could obscure readings from the subsurface structures they’re interested in mapping. Two nights ago, the team spent hours troubleshooting the old instrument, eventually realizing that it had been incorrectly calibrated. Luckily, an engineer from Geometrics, the manufacturers of SIERRA’s cesium vapor magnetometer, an instrument that measures magnetic field strength, drove up yesterday with a new fluxgate.

With SIERRA aloft, I followed Jonathan and Noah Athens, both from the U.S. Geological Survey, out to the field, where they would communicate with SIERRA while driving four-wheel all-terrain vehicles (ATVs). The aircraft would transmit flight parameter and magnetic data to radio receivers on the ATVs, which would then store the data onto a hard drive as a backup in case the computer on board the SIERRA failed or the aircraft crashed. Since following SIERRA’s flight along tightly spaced east-west lines would be unfeasible on ATVs, Jonathan and Noah planned to drive along a perpendicular north-south path, allowing at least one ATV to remain within range of the aircraft at all times.

Not long after Jonathan and Noah unloaded the ATVs, Jonathan received a call from the ground base station. Within minutes of takeoff, SIERRA began slowly losing magnetic data.  Soon, the rate of data loss climbed, until the ground base station completely lost all signal from the fluxgate aboard the SIERRA. After landing the aircraft, they wheeled it to the hangar for troubleshooting.

“Wow,” Jonathan said as he hung up the phone. “There’s so much we could do today.” He rubbed his chin, gazing intently at the vast desert stretched out before us.

After a few seconds of pondering the possibilities, he decided that Noah and I would collect magnetic data by foot along a line they had plotted based on previous surveys that hinted at the presence of an underground fault or fracture in the area. Hopefully the ground-based survey would capture the subsurface feature, which should appear as a distinct magnetic pattern, or anomaly, in the data.

Dry lakebed, or playa, with the Warmer Mountain Range in the distance.

Dry lakebed, or playa, with the Warmer Mountain Range in the distance.

We would take magnetic readings with a magnetometer pack, a bulky instrument resembling a cross between a backpack and a lawn chair. A bulb-shaped GPS antenna and a cylindrical cesium vapor magnetometer protrude a few feet from the top of the backpack on either side. The frame is aluminum, which is non-magnetic, so as not to interfere with the magnetometer readings.

Jonathan hoisted the pack onto Noah’s back, tightening the straps and securing the magnetometer console, which stores and displays the data, snugly around his waist.  Then Jonathan showed me how to use a handheld GPS to navigate our traverse, or the line along which we could collect data, which the team had programmed with the line’s endpoint.  I transferred our cell phones, keys, and water canisters into a knapsack that I would carry while walking at least a hundred feet in front of Noah–far enough to prevent our magnetic, electronic belongings from interfering with the magnetometer readings.  After double-checking that we had everything we needed, Jonathan drove off to rejoin the NASA engineers back at the airfield.

I wove my way through clumps of brittle sagebrush, breathing in their heady, medicinal aroma as I brushed against them. After nervously scaling a steep dune, I paused to look at the stretch of dry lakebed, or playa, below, and the hazy blue silhouette of the Warner Range far ahead. Then I made the slow, careful descent to the playa.

I continued walking, every now and then turning back to check on Noah and glancing down at the GPS to make sure I hadn’t veered off course. A few dull-hued rocks and animal bones occasionally interrupted the expanse of cracked, parched earth. Mirages of lakes rippled along the base of the mountains. After two miles, I reached the endpoint, where I stopped and waited for Noah.  Without the steady tread of my footsteps, the desert was utterly silent, as if to remind me even more of its desolateness.

Noah securing a magnetometer pack onto the author.

Noah securing a magnetometer pack onto the author.

Once Noah caught up with me, we both stopped to drink water. We decided to trade duties.  After fastening the magnetic pack onto my back, he quickly explained how to use the console. Then we turned around and made our way back to the start point.

The magnetometer pack hung heavily from my back, forcing me to lean forward awkwardly as I walked.  Toward the end of our hike, I struggled to trudge through the length of soft playa near the foot of the dune. The weight of the pack pushed me over the other side of the dune, leaving me with little choice but to slide and hope I didn’t crash on the way down. Once I reached Noah, I immediately began unfastening the pack from my shoulders, anxious to relieve myself of its weight. I had ventured on this expedition anticipating refreshing, picturesque hikes through nature. I still stood in awe of the desert’s surreal beauty, but now with an undiluted, unromantic appreciation for the physicality of fieldwork and the researchers’ passion for doing science even in challenging conditions.

That evening, Noah opened up his laptop and showed me the magnetic data we had collected on the playa. The screen displayed the readings as a curve, its two halves mirror images of each other, representing our hike to and from the endpoint.  A magnetic anomaly appeared as an undeniable peak emerging from each half. In other words, the researchers had successfully homed in on the subsurface feature they predicted to be located in the area. They would perform more of these ground surveys, collectively generating high-resolution mappings of geologically interesting regions.

Sometimes the team needed to respond to the unpredictable twists and turns of fieldwork with an equal measure of swift, yet purposeful, action.  Even with SIERRA grounded, the team collectively adapted, continuing to map Surprise Valley’s subsurface.  And now, reveling in my wrinkled, dirt-streaked clothes and the layer of grime on my freshly scraped skin, I could share somewhat in the satisfying exhaustion the team’s geoscientists experience following hours in the field, collecting data that in its own small, though significant, way, contributed to “great science.”

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A Valley of Surprises (Sept 3, 2012)

The Surprise Valley field expedition is an expedition in every sense. On the one hand, the team is trying to map underground faults and fractures beyond a region whose subsurface they’ve already studied in great detail. But analyzing the data in these new maps has itself proven to be an expedition. Although data analysis is one step in the pursuit of specific research questions, today it led them off course, toward new, unanticipated paths of inquiry. Finally, after a long night of troubleshooting, the team had begun the adventure of research. It’s what beckons them to the field year after year, in spite of the inevitable technical hurdles. With preliminary data, the team not only made headway in answering one of their main research questions–they even encountered a few surprises along the way.

Geometrics engineer Misha Tchernychev calculating the mathematical relationship between the raw and incorrectly calibrated compensation data from the flux magnetometer. He can then apply this equation to yesterday’s flight data to convert it to raw form, calculate the correct calibration, and apply this calibration to the raw data.

Geometrics engineer Misha Tchernychev calculating the mathematical relationship between the raw and incorrectly calibrated compensation data from the flux magnetometer. He can then apply this equation to yesterday’s flight data to convert it to raw form, calculate the correct calibration, and apply this calibration to the raw data.

Yesterday marked the first day of the team’s expedition to map the underground faults and fractures in Surprise Valley, California using SIERRA, a small aircraft capable of flying without a pilot onboard, or unmanned aerial system (UAS). Faults and fractures generate distinct magnetic patterns,or anomalies. Geophysicists can look at a set of magnetic readings for a region and readily distinguish those representing these subsurface features from those that don’t. But SIERRA and its maneuvers also produce magnetic anomalies. As you might recall from our previous postto compensate for anomalies associated with SIERRA, the aircraft is fitted with an instrument called a fluxgate magnetometer, which allows the team to subtract the appropriate magnetic field values based on SIERRA’s position at any given point in time. This removes the effects of the aircraft’s magnetization, which could obscure the magnetic readings from the subsurface features the researchers are interested in studying.

During the flight, the fluxgate yielded compensation data values that deviated far from what the team had expected. After removing the instrument from the UAS and spending hours troubleshooting it, NASA engineers Corey Ippolito and Ritchie Lee, Geometrics engineer Misha Tchernychev, and lead USGS scientist Jonathan Glen removed the instrument from SIERRA and spent hours troubleshooting it, eventually tracing the problem to an error in its calibration.

The team hoped that a technician at Applied Physics, the manufacturer of the fluxgate, would happen to be in the office on Labor Day so that he or she could provide them with the proper calibration. While they weren’t able to contact Applied Physics, they were able to get in touch with another engineer from Geometrics, the company that installed the cesium vapor magnetometer, at their headquarters in the San Francisco Bay Area. The engineer said that he could provide the team with a new, properly calibrated fluxgate, which he agreed to drop off with them at a halfway point, in the town of Redding. Just before 8:00 AM, two USGS researchers hit the road to Redding. To allow themselves time to retrieve the new fluxgate and correct the previous day’s data, the team called off the flight for the day.

Misha met Jonathan at the house where USGS researchers are staying this field season. They planned to determine the correct the calibration themselves by recording the magnetic field strength and direction that the fluxgate magnetometer measured as they moved it through a series of maneuvers. This would yield the mathematical relationship between the raw and improperly calibrated versions of the data, allowing them to convert yesterday’s data to raw data. The fluxgate’s measurements of the magnetic fields produced by the maneuvers would also enable Jonathan and Misha to determine the correct calibration, which they could then apply to the raw data from the first flight day. Once the two USGS researchers returned from Redding with the new fluxgate, NASA engineers could mount it on SIERRA for use in future flights.

Jonathan and Misha spent the entire morning on the front lawn, one standing and maneuvering the instrument while the other kneeled across from him, jotting down the instrument’s readings on a sheet of paper. Misha then fed the readings into a computer program to generate an equation reflecting the relationship between the raw and incorrectly calibrated versions of the data. He then applied the equation to the data from the first flight.

Map showing SIERRA flight lines through Surprise Valley. The team plans to do three central detailed surveys, with the UAS flying along tightly spaced, east-west lines in three polygonal sections running north to south in the center of the valley (colored polygons near the center of valley. SIERRA will also fly the perimeter of the valley and in a broad zigzag pattern across the entire valley to map its large subsurface features, particularly in the unexplored southern region.

Map showing SIERRA flight lines through Surprise Valley. The team plans to do three central detailed surveys, with the UAS flying along tightly spaced, east-west lines in three polygonal sections running north to south in the center of the valley (colored polygons near the center of valley. SIERRA will also fly the perimeter of the valley and in a broad zigzag pattern across the entire valley to map its large subsurface features, particularly in the unexplored southern region.

The resulting raw data appeared as a magnetic map, crisscrossed with grid lines showing yesterday’s flight path, the bright green lines representing magnetic anomalies, indicating faults and fractures below the surface. This field season, the team plans to do three central detailed surveys, with the UAS flying along tightly spaced, east-west lines in three polygonal sections running north to south near the center of the valley. SIERRA will also fly the perimeter of the valley and in a broad zigzag pattern across the entire valley to map its large subsurface features, particularly in the unexplored southern region. Next year, the experimental UAS will be able to perform a more detailed, accurate survey over the entire valley since it can fly closer to the ground, and its wider wingspan enables the cesium vapor magnetometer to be mounted further from the center of the aircraft, where electronics and instruments could produce magnetic noise. The experimental system is also electronic, meaning it lacks the numerous magnetic parts that comprise a combustion engine.  The team will even be able to turn off the electric mode and switch the aircraft to glide mode.

Yesterday, SIERRA surveyed the middle and southern central detailed regions. When Jonathan saw the data, he grinned broadly. Even the raw airborne magnetic data closely coincided with the ground-based data his group had gathered from the same region in previous years. After further sifting through the data, Jonathan observed that the pattern of structures buried below the regions mapped during yesterday’s survey looked very similar—essentially analogous—to that of structures on the surface along Summer Lake to the north of the valley. This pattern consists of a low-lying area, called a basin, which was formed when the Earth’s crust thinned and cracked as forces originating in the underlying mantle pulled it apart. This stretching resulted in one part of the crust thrusting upward, forming a mountain range, and an adjacent region sinking downward, forming a basin. The two structures collectively comprise a basin-range region. In Surprise Valley, the Warner Mountain Range meets a dry lakebed, or playa, and the Winter Rim Mountain Range meets Summer Lake. In both regions, numerous faults run parallel to the edge of the basin where it meets the range. Sheets of magma injected from the Earth’s core into the surrounding rock, a type of geologic structure known as a dike, run parallel to the faults, lying snugly alongside them.

Both Summer Lake and Surprise Valley share a similar structural pattern, the major difference being that while this pattern is visible on the surface of Summer Lake, it remains hidden underground in Surprise Valley, revealed only by magnetic mapping.  This hints that similar patterns may be found throughout the Basin and Range region, which spans much of the western United States. It may be possible that the magmatic intrusions that form dikes may play a role in the development of the basins in this area. Right now, the team doesn’t know whether the magma creates faults as it rises, or whether the crumbling of rocks along faults makes it easier for magma to flow through. This knowledge could point the team to how magmatic intrusions play a role in basin development in the area.

Jonathan pored over the map displayed on laptop throughout the afternoon, every now and then looking up, exhilarated, and gathering the other USGS researchers around his screen. Meanwhile, Misha holed up at Cedarville Airport, calculating the correct calibration from the maneuvers earlier today.  He returned a few hours later with the correct calibration applied to the raw data.  While the magnetic map based on the raw data was mostly clear, the edges appeared blurry.  When Misha applied the correct calibration, the resolution of the map image improved significantly.  The image he showed Jonathan centered on a feature that previous ground-based data had indicated to be two diagonally parallel segments arranged in a stairstep, or an echelon pattern. Now, the magnetic data revealed these actually represented only one fault. The two veins of the fault branched out from a single fault, which scientists wouldn’t have known if they hadn’t mapped the region below.

Magnetic anomaly (red line circled in brown) stretching over 30 kilometers through Surprise Valley, which the team detected during previous ground-based surveys of the area. They hope that SIERRA’s surveys will allow them to fill in the gaps on their map (arrows) and determine the anomaly represents a continuous structure or multiple diagonally parallel segments arranged in a stair step, or en echelon, pattern.

Magnetic anomaly (red line circled in brown) stretching over 30 kilometers through Surprise Valley, which the team detected during previous ground-based surveys of the area. They hope that SIERRA’s surveys will allow them to fill in the gaps on their map (arrows) and determine the anomaly represents a continuous structure or multiple diagonally parallel segments arranged in a stair step, or en echelon, pattern.

The feature that the team is most curious about appears on their maps as a magnetic anomaly stretching over 30 kilometers through the valley, which they detected during earlier ground-based surveys of Surprise Valley. Unlike the corrugated Surprise Valley Fault, which meanders along the base of the Warner Mountain Range, this feature runs an almost perfectly straight course. It also coincides with a number of major hot springs, suggesting that it plays an important role in the system of channels and pores the circulate fluid through the hot springs, or the geothermal system, of the valley.

In previous years, the team had collected ground-based magnetic data on the northern and southern sections of the feature. But with this data alone, they couldn’t tell whether the feature represented a single through-going structure or multiple en echelon segments. They hope that aerial surveys of the central detailed regions between the northern and southern parts will yield the missing pieces that will allow them to answer this question.

Looking at the raw data from the yesterday’s survey of the middle and southern central detailed regions, Jonathan spotted a magnetic anomaly continuing along the same direction as the anomaly he and Anne had mapped when they performed a ground-based survey of the area surrounding the southern part of the feature. So far, the data hints that the feature may in fact represent a single structure, but the team can’t draw any conclusions before SIERRA completes the map, at least of the feature of interest, by surveying the north central detailed region, which the team has planned for it to do tomorrow.

Knowing whether or not the feature is continuous is important, since the magnitude of an earthquake that can occur along a fault is determined primarily by the length of the fault. The longer the fault, the larger the earthquake it causes when it ruptures. In other words, if the feature the researchers are interested in is long and continuous, it will cause a much larger earthquake than if it were partitioned into segments. A continuous fault also means a continuous channel for geothermal fluids, a dangerous scenario, since a hazardous groundwater zone high in mineral content sits in the middle of the feature. Since continuous and en echelon faults differ in the type of earthquakes they produce, knowing the feature’s structure will also help refine predictions of how likely and how damaging earthquakes could be in the region.

USGS lead scientist Jonathan Glen (center) sharing his findings with other USGS researchers

USGS lead scientist Jonathan Glen (center) sharing his findings with other USGS researchers

As Jonathan continued to navigate through the data, the two USGS researchers returned with the new fluxgate, which they handed off to the NASA engineers to install in SIERRA tonight so that the aircraft can fly first thing tomorrow morning.  The team excitedly awaits the results of tomorrow’s survey. While no one can guarantee that they won’t run into any more technical mishaps, the alternative possibilities—the glimmer of an answer to a research question, a surprise discovery–make the adventure worthwhile.

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Smoothing out the Kinks | Sept 2, 2012

How does science work? Though romanticized as a string of exciting, accidental discoveries, in reality, the bulk of scientific research happens in the prelude to discovery–the humbler, though no less exciting, process of troubleshooting. The first day of an expedition is typically the most hectic, as researchers settle into the rhythm of fieldwork, smoothing out the kinks along the way. The Surprise Valley team encountered its fair share of issues to troubleshoot today.

SIERRA preparing for takeoff

SIERRA preparing for takeoff

The first day of the field season began at 6:30 AM this morning, with the team members loading the equipment and driving to nearby Cedarville Airport. There, they would send SIERRA, a small aircraft capable of flying without pilot or crew, known as an unmanned aerial system (UAS), on its first flight mission to collect magnetic data along a preprogrammed course using an instrument called a magnetometer. The team will use this data to map the underground faults and fractures in Surprise Valley, which may help circulate hot water and minerals throughout the numerous hot springs in the area. This information will be critical for predicting the likelihood of earthquakes in the region and the damage they may do, informing land and water use decisions, and tapping the hot spring fluids as an energy resource.

When the U.S. Geological Survey (USGS) arrived at the airport, SIERRA engineers and aircraft itself awaited them, as did Corey Ippolito and Ritchie Lee, both from NASA-Ames Research Center, who developed the scientific instrumentation, or payload, which SIERRA uses to collect magnetic data. The team will integrate the payload into a new experimental UAS next year which can make higher-level cognitive assessments of the sensor data it receives, allowing it to plan and perform a complete survey mission without human intervention. The vehicle will adjust its flight path according to magnetic fields and environmental conditions in order to maximize data collection in areas of interest and reduce flight time over other areas. With a specified pre-programmed flight path that does not adapt to the magnetic environment, SIERRA could miss important features that will not be apparent until after the data is downloaded post-flight. The team will later compare the datasets collected by the two systems with the goal of developing a cheaper, more effective airborne survey system.

Both groups of engineers had already set up the ground base station, where they would communicate with SIERRA through signals relayed from the aircraft to their computers. At about 9:00 AM, SIERRA’s engine rumbled to life, its propeller whirring vigorously. Just as fast as it sped down the runway, it was aloft, disappearing into a tiny glint of sunlight above the hills along the eastern edge of the valley.  A pilot in a separate aircraft, the chase plane, took off after the SIERRA, which he would monitor throughout its flight per Federal Aviation Administration regulations.

SIERRA began by flying north, south, east, and west in a box-shaped path. It then flew within the box, first undulating up and down, then banking to the left and right, in a flight sequence known as a compensation box. An instrument on SIERRA called a fluxgate magnetometer would provide information about the magnetic field at every possible position of the aircraft, known as compensation data. When the team performs a magnetic survey, they can subtract the appropriate magnetic field values based on SIERRA’s position at any given point in time. This would allow researchers to correct for variations in the magnetic field that can arise when SIERRA maneuvers, which could obscure signals generated by the geologic structures the scientists are interested in. Unlike the cesium magnetometer in the wingtip, which tells researchers only the strength of the field, the fluxgate also indicates the direction of the field, parsed into three different axes.

The aircraft then began a detailed survey, collecting magnetic field data along tightly spaced east-west lines from two of the three regions that Jonathan Glen of the USGS and Anne Egger of Central Washington University, the lead geoscientists on the project, had found magnetically interesting according to ground-based studies they performed during a previous visit to Surprise Valley.

Corey Ippolito, co-principal investigator on the Surprise Valley project and developer of the SIERRA payload system (front), with Ritchie Lee (rear), monitoring SIERRA’s flight parameter and magnetic data from the ground base station

Corey Ippolito, co-principal investigator on the Surprise Valley project and developer of the SIERRA payload system (front), with Ritchie Lee (rear), monitoring SIERRA’s flight parameter and magnetic data from the ground base station

Meanwhile, the SIERRA ground crew monitored how the aircraft moved through the air based on magnetic field direction data collected by another type of fluxgate magnetometer, relayed from an antenna installed on the aircraft’s underbelly. SIERRA also sent information on its flight parameters, such as its altitude, GPS coordinates, and speed. At the same time, the USGS and NASA engineers’ computers received the scientific data SIERRA collected in addition to flight parameter data, transmitted by an antenna on the nose of the aircraft.  Besides the compensation data, these include the magnetic field data measured by SIERRA’s magnetometer, as well as the UAS’ distance from the ground, collected by an instrument called a laser altimeter. Knowing SIERRA’s altitude will allow the team to correct for variations in magnetic field strength due merely to differences in distance from a magnetic source, since the strength of a magnetic field fades the further one moves away from the source.

Out in the field, SIERRA relayed the same flight parameter and magnetic data it relayed to the science payload team to an ATV equipped with a computer, GPS, and a radio receiver. SIERRA transmits payload data to the radio receiver, which is then stored on a hard drive on the ATV. This ensures that the team has a backup in case the computer on board the SIERRA fails or the aircraft crashes. Since following SIERRA’s exact path is unfeasible on ATVs, a researcher in Jonathan’s  lab drove along a north-south path, perpendicular to SIERRA’s flight path, which allowed the ATV to remain within range of the aircraft at all times.

SIERRA landing

SIERRA landing

After SIERRA landed the wireless communication system that the payload engineers had set up to download flight parameter and magnetic data from SIERRA malfunctioned. In the past they had discussed transferring data directly from SIERRA through a network cable, although in the end they opted to use a commercial off-the-shelf (COTS) wireless system, or a wireless system available for sale to the general public. COTS products are designed to be easily implemented into existing systems without the need for customization. With the wireless system, the engineers could avoid directly accessing the aircraft’s sensitive instruments. However, the COTS system was not able to withstand SIERRA’s vibrations during the flight test.  With the wireless system down, the payload team developed a workaround that requires the aircraft to be physically tethered to the ground station to download the data after each flight.

Project co-principal investigator Jonathan Glen (lower left) with NASA and Geometrics engineers, troubleshooting SIERRA’s malfunctioned wireless system, which prevented the USGS and payload systems engineers from remotely downloading flight parameter and magnetic data to their ground base station computers.

Project co-principal investigator Jonathan Glen (lower left) with NASA and Geometrics engineers, troubleshooting SIERRA’s malfunctioned wireless system, which prevented the USGS and payload systems engineers from remotely downloading flight parameter and magnetic data to their ground base station computers.

Meanwhile, the compensation data from SIERRA’s fluxgate magnetometer yielded highly unusual results. The data from a test of the fluxgate when it was first installed looked reasonable to the team, with variations not too far from expected values. They did notice some anomalies, which they believed they could solve only by recalibrating the instrument or remounting it away from magnetic noise, signals from magnetic sources that may distort the magnetometer’s measurements, called magnetic noise. Currently the fluxgate sits beneath the wing, not at the tip, but toward the center of the aircraft, which houses numerous electronics. Both recalibrating and repositioning the fluxgate would be prohibitively expensive.  Instead, the researchers decided to use the instrument as it was calibrated. The compensation still corrected for SIERRA’s magnetic field, but not as precisely as it should. The researchers hoped that the remoteness of Surprise Valley, away from steel-framed buildings, electric lines, and other magnetic sources would enable them to make minor adjustments to correct for aircraft-related noise.

Corey (left) and Ritchie (right) troubleshooting the fluxgate magnetometer

Corey (left) and Ritchie (right) troubleshooting the fluxgate magnetometer

At the end of the day, the payload systems engineers hauled the base station computers to the USGS group’s house, where they spent hours poring over the compensation data, trying to pinpoint the source of the anomalies.  Then an idea occurred to the team: maybe the problem was limited only to the fluxgate and not dependent on the aircraft, which they could confirm by examining just the fluxgate in the house, where magnetic noise is minimal. If working properly, the fluxgate’s measurements should closely reflect the Earth’s magnetic field, a known value. If they don’t, then the problem must be due to the fluxgate itself.

Jonathan and Corey called SIERRA lead engineer Randy Berthold to ask if one of the SIERRA engineers could remove the fluxgate magnetometer from the aircraft so that they could run the test on the software and hardware in isolation. Once Randy agreed to meet them at the Cedarville Airport in a few minutes, past eight at night, Jonathan, Corey, Ritchie, and Geometrics engineer Misha Tchernychev bolted out of the house, jumped into one of the trucks, and sped to the airport. There, Randy and another SIERRA engineer, Ric Kolyer removed the fluxgate, which the USGS, NASA, and Geometrics crew then took home for a long night of troubleshooting.

Team members camped out with the fluxgate in the dining room, exhausted yet still talking and joking animatedly between swills of coffee.   After a few hours, the team discovered that the fluxgate could collect data in two modes—calibrated or raw. The fluxgate was currently, as during the flight, in calibrated mode. When they team took measurements in this mode, they saw magnetic field values far from those of the Earth. When they switched the instrument to raw mode, they saw the values they expected. Clearly the fluxgate’s calibration needed fixing.

Tomorrow morning, the crew will try to determine the correct calibration themselves by moving the fluxgate through different maneuvers, which will yield the mathematical relationship between the raw and improperly calibrated versions of the data, allowing them to convert today’s data to raw data. They hope that a technician from Applied Physics, the manufacturer of the fluxgate, during tomorrow’s Labor Day holiday, in which case they can provide the proper calibration, another equation that the team can apply to the raw data from today to generate properly calibrated results. Otherwise, the team can calculate the correct calibration themselves based on the readings from the fluxgate maneuvers. Ideally, the technician may even be able to drive a new instrument up from the Bay Area so that the team can avoid having to undo and redo the calibration for each dataset.

“Field work can be very stressful,” said Jonathan. “It requires a certain kind of temperament. I’ve learned to live on very little sleep.” He paused, then grinned. “But that’s the best part of fieldwork.  I’m so thrilled to get to work with Corey and Ritchie.  They’re really great…. We’re really privileged to be able to do the work we do.” What he said was true, even when “the work” is troubleshooting. Imagine how much more so on a day of smooth operation.

 

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Introduction: Mapping Underground Faults and Fractures in Surprise Valley

Tucked in the northeastern corner of California, Surprise Valley is a quiet rural community of about 1,000, set amidst a vast high desert landscape dotted with hot springs and dry lakebeds. But there’s far more going on below the ground than you’d ever know, standing above. From September 1-13, a team of scientists and engineers will collect magnetic data using ground surveys and an aircraft that can fly without a pilot or crew on board, called an unmanned aerial system, or UAS, to map the geophysics below the surface of Surprise Valley.

Why create such a map when hints of the area’s seismic history are plainly displayed on its surface? The corrugated Surprise Valley Fault snakes 85 kilometers along the Warner Mountain Range, the landscape is pocked with smaller surface scars, called fault scarps, that indicate movement along faults, and hot springs billow steam–proof that the area is anything but quiet.

But although some faults and fractures are visible on the surface, some remain completely hidden underground. And even if researchers know where the hot springs are located, they want to understand how hot spring fluids flow through the network of pores and channels underground. Investigating this geothermal fluid circulation system includes identifying faults below the surface that might conduct the hot mixture of fluids and minerals found in the hot springs. These faults also have the potential to rupture during an earthquake, and the detailed studies will help refine predictions of how likely and how damaging earthquakes could be in the region.

Later, the team will compare magnetic data to topographic data they’ve already collected in order to correlate subsurface structures to areas of surface offset, or displacement from the fault center, which indicate active faulting. At the end of the U.S. Geological Survey (USGS)-led, NASA-funded project, which includes a second field session scheduled for next year, they’ll produce a 3-D map that will provide geophysical data on Surprise Valley at a level of detail yet to be achieved for the area. This map will be crucial for predicting the likelihood of earthquakes in Surprise Valley and the damage they may do. The Surprise Valley municipal government can also use the map to inform land and water use decisions, since toxic water zones have been identified in the area, as well to help tap the geothermal system as a sustainable energy source.

The team, which includes scientists and engineers from USGS, NASA-Ames, Central Washington University, and Carnegie Mellon University, will measure magnetic fields using ground surveys and an unmanned aerial system (UAS) to map the geophysics below the surface of Surprise Valley.  Over the years, they’ve collected a wealth of magnetic data by foot and small, four-wheel all-terrain vehicles, or ATV. But the areas they can safely and feasibly survey on the ground are limited. They can’t walk through private lands, dense vegetation, or hot springs, for example. Geoscientists have typically addressed this challenge by contracting pilots to collect data along a specified flight path. Not only are these manned aerial surveys costly, they require pilots to fly at dangerously low altitudes. That’s why the Surprise Valley team will collect data with a small, lightweight, low-flying UAS known as SIERRA (Sensor Integrated Environmental Remote Research Aircraft, photo here). While flying along a preprogrammed path, the NASA-developed SIERRA will relay the data collected by a magnetometer in its wing to a ground station computer. (You can view photos of the team testing the ground base station systems at NASA-Ames Research Center here.) SIERRA is available for other research projects involving the collection of data from inaccessible swaths of land.  Scientists have already employed SIERRA in the NASA-funded Characterization of Arctic Sea Ice Experiment (CASIE) to assess the decline in the ice covering Alaska’s Beaufort Sea.

While SIERRA offers a safer alternative to manned flight, it still has some limitations. With a specified flight path, both manned aerial surveys and UAS run the risk of bypassing interesting geological features. Next year, the Surprise Valley team will collect magnetic data using NASA’s Swift “smart” UAS. The major difference between the two platforms is that an on-board system navigates Swift based on feedback it receives on both magnetic data and environmental conditions, such as wind speed and direction, or obstacles in its path. The system, known as an adaptive payload system, will integrate the magnetic data that Swift’s magnetometer has collected with magnetic datasets into an algorithm that will then “decide” how to adjust Swift’s flight path to maximize data collection in areas of interest.  The team will compare the datasets collected by the two UAS platforms with the goal of developing a cheaper, more effective airborne survey system.

This field season, the team will run additional tests on SIERRA’s ability to correct for magnetic noise associated with the magnetization of the aircraft that would otherwise obscure signals arising from geologic structures we’re interested in. Faults and fractures generate magnetic fields that deviate from those emitted by regions of the valley that lack these features, but so do the aircraft and its maneuvers. SIERRA needs to subtract these readings to ensure that any anomalies that appear in the magnetic data reflect solely features below the surface. 

The researchers will then fly the aircraft in a broad zigzag pattern across Surprise Valley, collecting magnetic data from large features in previously unexplored areas. These data will be important in planning next year’s mission, when Swift will conduct more detailed surveys of the region. The team will concurrently test the payload system by comparing these data against the data collected by Swift.

While airborne magnetic surveys offer complete coverage of an area, there are still reasons to do ground-based surveys. Since a magnetic field weakens with increased distance from the magnetic source, aerial surveys can only detect large fields produced by the gross characteristics of a source below the surface. On the ground, researchers are able to pick up on the more subtle fields produced by a source’s smaller features. During both field sessions, the team will continue to collect magnetic data by foot and ATV (photo) in addition to UAS and will perform gravity measurements along some of the same subsurface structures.  They’ll also drill rock cores to measure remnant magnetization, a record of the magnetic fields at the time the rocks formed, and collect samples from the area to determine density and magnetic susceptibility, which is a measure of how “magnetizable” a rock is. These data will collectively be used to develop gravity and magnetic models to determine the geometry of structures below the surface.

The National Center for Airborne Laser Mapping has already mapped Surprise Valley’s surface features, or topography, using airborne lidar, a highly sensitive technology that can make out even tiny features—visualizing objects and distances as small as a few centimeters. Lidar bounces a laser off the landscape, making a detailed 3-D topographical image. Unlike magnetic field data, which can identify structures below the surface but tells us nothing about their activity, lidar can distinguish active from inactive structures, since only structures that have been active in the recent past produce fault scarps and other areas of surface offset that would still be visible. Otherwise, erosion and sedimentation would have wiped them out. After tying surface offset to subsurface structures, scientists can develop models for the area’s seismic activity.

On this blog, also hosted at NASA’s Mission: Ames and Scientific American’s Expeditions, we’ll share updates on daily missions, glimpses of life in the field, and profiles of individual team members.  We’re excited that you’ll be joining us!

All photos by Melissa Pandika.  

About the Author: Melissa Pandika is a journalism master’s student at Stanford University.  Previously, she studied molecular and cell biology at the University of California, Berkeley and investigated how highly aggressive brain tumors evade therapies that block blood vessel growth at the University of California, San Francisco.

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