GLASS field notes

The morning of the 10th was chilly and overcast with a diffuse light which reduced the surrounding terrain to a featureless, flat, white. As the team waited for conditions to evolve to a point which was safe to fly, they supported the breakdown of the camp which had been home for nearly two weeks.

By early afternoon two short Twin Otter flights had whisked them out of the isolated Constellation Inlet and deposited them safely back in to the relative metropolis of Union Glacier. The gear, much too big to be flown, was pulled on a Lehmann sled by a Tucker snowcat. While this meant the gear's return voyage was closer to 5 hours compared to the team's 10 minute teleportation, the slow caravan provided the chance for one more interesting science opportunity: the GPR sled which had so thoroughly investigated the Constellation Inlet region, was going to be hitched to the sled and operated for the entire return trip to UG. By combining all of the batteries planned to be return into one supper battery (4 x bigger than what the GPR typically used) it was estimated that the GPR would have enough power to capture that entire trip. This opportunity to capture such a large transect over unique and varied portions of the glacier would serve as a victory lap after weeks of successful data collection. As of the end of the 11th the GPR was confirmed to have fared well on the return trip and the data was still in the process of being ingested and analyzed.

Once back in Union Glacier, thoroughly showered and well rested after a good nights sleep, the GLASS team awoke to one more day of wrap up activities before a planned flight out on the 12th. The day began by unloading and sorting the mountain of gear by how and where it would be shipped to. Labeling and weighing the more than 2 tons of equipment brought in for the campaign in order to advise ALE on how things would need to be shipped back home to Caltech. Once unpacked and repacked, Auden and Soyeon took charge of downloading the data off of the 500 Stryde nodes which had been recovered. This array, which they'd been key in both the deployment and recovery of, had spanned several lines ~9 km in total length in CI. It will be used in conjunction with the DAS data to create the movie of the grounding zone.

As the team spends its final night in Antarctica, they're taking a moment to reflect on the work accomplished and the unique environment that made it possible. The expedition ends here, but the lessons learned will guide many projects to come.

The past two days marked the closeout of the GLASS field campaign at Constellation Inlet, with the team shifting from active surveying, to preparing the site and the instruments for the weeks of autonomous data collection ahead.

On the afternoon of December 9, the final PEG shots were fired, officially completing the active-source survey. With this final sequence recorded across the full array, the seismic dataset now spans stationary tidal shots, the full 5 km mobile survey, and repeat-source measurements, providing a rich foundation for tracking grounding-line behavior.

With the active survey complete, attention turned to securing the long-duration instruments. The DAS system was buried and secured for continuous operation. Over the coming weeks it will continue to listen for icequakes and other ambient seismic signals, providing a steady stream of information until it is recovered in mid– to late January. The GNSS stations and 20 SmartSolo nodes will remain in the field as well, collecting continuous measurements before being retrieved and shipped back for post-season analysis.

Meanwhile, camp teardown began in earnest. Tents were struck, equipment packed, and the Stryde node field fully recovered in preparation for departure. With weather expected to deteriorate, the field team will depart a day earlier than scheduled. Tomorrow morning, the Twin Otters return to bring the group back to Union Glacier, marking the end of on-site operations and the beginning of the science phase to come.

Constellation Inlet, Day 7

Day 7 marked the transition into full mobile operations for the GLASS active-source campaign. After days of stationary PEG shots, the team shifted to the survey phase, mobilizing the power system on a sled and mounting the PEG onto the back of the Tucker. Beginning 3 km down the fiber line, the group worked steadily upslope, firing shots in 200-meter increments and completing 1.6 km of the transect by day's end. Each stop added another controlled seismic source to the growing dataset the arrays have been listening to throughout the week.

Alongside the PEG work, the GPR team completed two additional transects in regions adjacent to the fiber, extending radar coverage of the grounding-line environment. The fiber-optic effort also made meaningful progress: 4.5 km of new cable was deployed and successfully spliced to the 1.5 km installed yesterday, forming a continuous 6 km segment that the OptaSense DAS system will monitor over the coming days.

After several weeks of nonstop effort—first deploying every array in the GLASS experiment, then sustaining round-the-clock PEG operations during the stationary experiment—the team took a moment to breathe. With warm weather, a surplus of bamboo poles, and a rare open afternoon, the group wrapped up operations early and held an impromptu Antarctic Tiki party at camp. Spirits were high as the team prepared for the final push to complete the mobile survey and transition into recovery and camp-breakdown activities.

Looking ahead, if the mobile survey concludes ahead of schedule, the team may relocate the repeating-source experiment to a downstream site to complement the tidal-cycle shots collected upstream earlier this week.

Constellation Inlet, Day 8

The eighth day in the field brought the GLASS team into the final stretch of the active-source campaign. By morning, preparations were underway to complete the remaining 3 km of mobile PEG shots, each stop spaced roughly 200 meters apart along the fiber line, forming the distributed shot pattern needed to illuminate the subsurface in detail. As these shifts continued, the team also worked to identify a downstream location suitable for the upcoming repeating-source deployment, which will capture tidal-scale deformation over a concentrated ~12-hour window.

Throughout the day, the GLASS arrays continued listening as the PEG moved steadily down the line. By afternoon, the crew reached a major milestone: survey shots along the entire fiber route were completed, marking the end of the planned activities for the campaign. In parallel, the GPR team conducted two additional transects near the fiber line, extending the cross-line coverage and adding further context to the grounding-line region.

The team also began measuring the full 6 km optical fiber using the OptaSense DAS system, taking advantage of ongoing PEG shot sequences to characterize signal quality across the new line. Meanwhile, Soyeon Park and Thatcher Chamberlin collected and reviewed GNSS station data, comparing measured motion with expected glacial velocities from InSAR and observing vertical variations linked to tidal cycles.

Constellation Inlet, Day 4

Day 4 marked a major transition point for the GLASS campaign, with the final pushes to complete instrument deployment and move into the active survey phase. The day began with several key objectives: finishing the STRYDE node array, conducting an early-afternoon GPR transect, beginning deployment of the SmartSolo geophone array, analyzing PEG data from the high-tide and low-tide shot sets, and preparing for the active-source survey operations scheduled to run continuously over the next several days.

By the end of the day, the STRYDE array reached full deployment—all 500 nodes installed across the survey area. This achievement officially cleared the way for the active-source portion of the campaign to begin. Seventeen of the twenty SmartSolo nodes were also deployed, with the remaining three scheduled for completion tomorrow. Once these are in place, every major array in the GLASS experiment will be active in the field. Beginning midday, the team entered the cadence that will define the next several days: PEG shots for approximately 50 minutes every two hours, running 24 hours a day through December 5 to capture the full tidal range. Discussions are ongoing about the potential deployment of additional fiber arrays, and the team is also refining the plan for PEG transport during the mobile survey scheduled to begin on December 6.

The day also brought a set of especially compelling scientific results, with both the DAS and GPR systems capturing clear signatures relevant to grounding-line behavior. These findings are summarized below, directly in the words of the team members leading each analysis.

Auden Reid-McLaughlin — Early DAS Results

"We are looking at a simple schematic of the ray paths of the seismic waves through the ice and reflecting back up to our receiver. Depending on the grounding line location, the amplitude of the reflection will change with the tides because of the different reflectivity between ice and rock on the grounded side and ice and water on the floating side. By taking the difference of the recorded reflection, we can clearly see the upstream and downstream extents of the grounding line.

The map view shows where these points are in space. As we perform more shots at different tidal heights, we will begin to fill out the path of the grounding line migration upstream and downstream. We will get a time lapse of the position versus time, which has never before been achieved."

Thatcher Chamberlin — GPR Results

"This is the radargram from our second transect with the SORA ice-penetrating radar. We're really excited about this result! We were traveling by snowmobile at 7 kph, so this radargram covers about 3 km—1.5 km upstream and downstream of camp. The thing to look at here is the deepest, brightest reflections in each column—those are reflections from the ice bed."

"What's really interesting is that the depth varies significantly across this relatively short 3 km section. There's a good bed reflection at about 1150 meters depth at time = 0, which we can see beginning to slope down as the snowmobile heads downstream. We lose the reflection for a while, but when we pick it back up, the depth is much deeper at about 1600 meters! The ice stays about that thickness for the rest of the transect, and the bed reflection becomes much brighter (high return power), most likely indicating a strong reflection off conductive salt water. In other words, this radargram shows us crossing the grounding line.

We got a picture similar to this yesterday, but today's image has a clearer upstream bed and comes from a single transect instead of an assembly of shorter sled rides."

Constellation Inlet, Day 5

Day 5 centered on completing the remaining SmartSolo deployments, conducting an afternoon GPR transect, and continuing the around-the-clock PEG shot schedule for the active survey phase. With the final three SmartSolo nodes placed, the team officially completed all planned array installations for the GLASS campaign—an important milestone that marks the end of the deployment phase. Throughout the day, PEG shifts continued on a two-hour cadence, with the team trained to verify that the DAS system remained in a healthy recording state and fully briefed on safe PEG operations.

Another set of GPR measurements was collected in the afternoon, including a transect along part of the main line and a second line offset and parallel to it, adding spatial coverage to the radar dataset. Discussions continue regarding whether additional fiber sections may be deployed, and the team is evaluating options for efficiently transporting the PEG system once the mobile survey begins on December 6. With all major arrays now in the field and the active source operations underway, the project is well positioned to enter the next phase of the campaign.

Constellation Inlet, Day 6

The sixth day in the field marked a significant turning point for the GLASS campaign. After nearly two days of continuous, round-the-clock PEG operations, the team wrapped up the first phase of the active-source experiment just after midnight on December 6. For 50 minutes every other hour, across 50 straight hours, the PEG delivered seismic pulses while every array on the ice listened intently. This cadence created an exceptionally rich dataset that will serve as the foundation for understanding grounding-line behavior at Constellation Inlet. With this milestone reached, the team now shifts focus to the second phase of the active-source campaign: the survey. Beginning tomorrow, the PEG will "go mobile," stopping approximately every 200 meters along a 5 km transect. This distributed set of shot points will allow the team to construct a far more detailed view of the subsurface, revealing the structure of the ice and bed with unprecedented clarity.

Elsewhere on the ice, the full set of GNSS stations completed their first data collection cycle, and the team has begun reviewing these early measurements. In the afternoon, an additional GPR transect was completed, extending the radar coverage of the grounding-line region. The team also began deploying a second optical fiber as a stretch goal to support OptaSense DAS measurements—successfully installing 1.5 km before identifying and isolating a break that will be spliced tomorrow.

The day was not without concern: late in the morning, the PEG system experienced a mechanical breakdown. Given its central role in the active-source experiments, the issue initially appeared serious. But within a few hours, the team's engineers were able to diagnose the fault, implement a repair, and bring the system fully back online—an impressive recovery that kept the campaign on schedule.

With all systems now poised for tomorrow's survey, the team ends Day 6 with momentum, resilience, and a growing dataset that's beginning to illuminate the hidden landscape beneath the ice.

Constellation Inlet Arrival, Primary Field Site

By late afternoon on Friday the 28th, all gear had been repacked, weighed, and staged for an early departure to the newly established field camp at Constellation Inlet. The morning meteorology report cleared the way, confirming a post-lunch flight window aboard a pair of Twin Otter aircraft. With the timing set, the team spent the next few hours making final preparations, including loading the Tucker-pulled sled with the bulk of the scientific equipment that would take the slower, overland route to meet them at the site.

After a final lunch in the incomparable Union Glacier dining tent, the team boarded the two aircraft and lifted off on the short ten-minute flight eastward. From the air, they caught their first glimpses of the terrain beyond Union Glacier—broad crevasse fields radiating outward from the mountains, the Tucker making its steady crawl across the ice, and eventually the first outlines of the Constellation Inlet camp itself. The most prominent feature was the ALE-deployed field laboratory positioned at the edge of camp, a central workspace that would support the scientific operations for the weeks ahead.

Upon landing, the team received a brief orientation to camp life before the Tucker arrived, allowing them to unload and stow the incoming gear. With logistics squared away, the group turned immediately to the work they had traveled so far to begin. The focus for this "Day 0" period centered on establishing initial infrastructure: deploying the GLASS camp power station, beginning construction of the ground-penetrating radar (GPR) sled, and setting up the DAS instrument to continue final checkout testing. The evening brought a sense of momentum—the first steps completed toward the full scientific campaign.

Constellation Inlet, Day 1

The first full day in the field brought steady progress across all major systems. Early in the day, the team deployed the GPS base station and radio repeater near camp, establishing the communications and positioning backbone for the work ahead. The 5 km bamboo pole line—marking the GPS coordinates of the planned fiber-optic route—was fully installed, providing a clear visual reference across the ice.

By midday, approximately 1.5 km of test fiber had been laid out, with checks confirming good coupling to the ice surface. The DAS system was brought online and began collecting initial measurements along this section. A PEG test at a 1 km offset followed shortly after, giving the team a first look at source behavior and transport characteristics in the snowpack.

The day concluded with successful assembly and activation of the GPR sled. Its first test immediately produced encouraging results, imaging the bed at roughly 1600 meters depth and setting the stage for the upcoming grounding-line transect.

Constellation Inlet, Day 2: Full 5 km Fiber Successfully Deployed

Day 2 began with several core objectives: initiating deployment of the STRYDE node array, evaluating PEG source characteristics from the back of the Tucker, and continuing GPR tuning ahead of the full transect. The GPR sled completed several short test runs, performing well and revealing a range of bed depths along the upstream portion of the track, though additional tuning will be needed. STRYDE deployment began shortly afterward but was paused when the deployment system's batteries ran low; during this downtime, the team shifted effectively to other tasks and deployed four GNSS stations, nearly half of the planned ten-station array.

A PEG test using the smaller 18-inch plate was conducted from the back of the Tucker, with data recorded on the test fiber via the low-SWaP system to support active-source characterization.

The day's major milestone was the successful deployment of the full 5 km primary fiber line across the grounding line, a key component of the larger GLASS measurement campaign. With steady progress across multiple instruments, priorities were set for continued STRYDE deployment, further GPR tuning, and PEG data analysis in the days ahead.

Constellation Inlet, Day 3

Day 3 focused on continuing STRYDE node deployment, completing the tap test on the initial 1.5 km fiber section, finishing installation of the remaining GNSS stations, building the DAS power station, and relocating the DAS system to the start of the 5 km fiber line. The team also planned a low-tide GPR transect and prepared to deploy the stationary PEG stand at the –0.5 km point upstream of the DAS array.

By the end of the day, approximately 330 STRYDE nodes had been deployed, with full array completion expected tomorrow. The fiber tap test was completed successfully, and both the DAS system and its power station were relocated and set up on the 5 km line. The low-tide GPR transect produced clear images along the entire route, with additional transects planned as resources allow. The stationary PEG stand was installed at the –0.5 km mark, and the team prepared late-night shot sets aligned with high and low tides to evaluate the planned shooting location.

Antarctica Arrival, Part 1

8:15 was the predefined pickup time for the airport, but well before then team members began lining their gear up in the lobby of the Cabo de Horno hotel. The row of red gear bags, holding the warmest set of outer layers issued to the team by ALE, served as a tally of those eagerly awaiting the imminent departure. Like clockwork, the bus arrived and with a precision necessary for the blustery morning, the team loaded their bags onto the vehicle and set off to the airport. Airport security check-in ran smoothly and the short wait at the terminal passed quickly as eager members of many teams introduced themselves and chatted about how fate had conspired to bring each of them to this point. Small vans delivered groups of 9 at a time to the plane for boarding as gusty winds swirled around its landing gear and boarding staircase. Gear was stowed, seats were taken, and then, at 12:30 local time, the plane took off. Excited conversations faded to a mellow tone and some expected dozing as the initial adrenaline rush subsided. At two and a half hours into the flight however, the first trace of Antarctica became visible and the energy level soared once more.

Soon dense ice pack and small mountain peaks streamed forth as people pressed against windows to witness the first approach. Over the next hour and a half the ice pack solidified into continuous, white, glacial sheets and small peaks gave way to the Sentinel Mountain range and Mt Vincent, the tallest peak in Antarctica. Fully in awe of the arrival of this new world the plane began its descent to Union Glacier and everyone donned their cold weather gear in preparation of those first steps out onto the fabled blue ice runway which had been spoken of for so long. The final descent into Union Glacier presented even more alien terrain with patches of blue ice broken up by crevassed regions seemingly bursting forth from within. The plane's wheels touched briefly, hesitated, then touched again. Decelerating to a slow crawl the call came over the intercom which all had waited for: "Ladies and gentlemen, welcome to Antarctica."

Antarctica Arrival, Part 2, Union Glacier Camp

Union Glacier Camp

The following two days in Union Glacier were focused on one primary objective: make sure all of the subsystems were ready to go into the field the morning of 11/29. The execution of this plan fell into place around the UG daily agenda. Meals at 0800, 1300, and 1900, quiet hours from 2300 to 0700. The major subsystem team groups divided up and focused on their assigned areas. The AP Res and towed radar system were checked out and measurements taken at Union Glacier. The GNSS stations had their power systems evaluated by ALE staff and had all of its batteries charged and installed so that they were ready to deploy. SmartSolo and STRYDE geophones were charged and several units were deployed to a large open area known as "The Playground." The active source was fit checked with its stationary mount and also with the ALE vehicles tow hitch. Finally the DAS and its power system underwent a series of tests, culminating in a full system check where the DAS power system, including batteries and solar panels, were used to operate both the lowSWAP DAS and traditional Optasense and DAS in order to support the evaluation of how well the deployment system coupled the fiber to the ice. By mid-day on the second day most systems (other than the large DAS set) had already concluded and much of the team's focus pivoted to beginning to repack all the equipment in advance of the move down to Constellation Inlet planned for 11/29.

Pasadena Team Departure

The morning of November 22nd began quietly, with the eight Caltech/JPL members of the GLASS team gathering at 8:00 a.m. at the loading dock of Caltech's Resnick Sustainability Center. The moment carried some weight: eleven months had passed since the project was selected by the Brinson Exploration Hub, and exactly ten months since the project kick-off. Now, the bulk of the team was setting off for Chile, the final staging point before Antarctica.

With the other three members of the eleven-person field team already on the ground in Chile, the Caltech contingent began a 33-hour sequence of flights—first from Los Angeles to São Paulo, then onward to Santiago, and finally to the southern city of Punta Arenas, arriving at 3:30 a.m. on November 24th.

Bleary-eyed but relieved to see all 20 checked bags arrive intact, the team stepped out to a faint, early glow on the eastern horizon and made their way to the hotel. A few hours of rest awaited them before they would begin the final preparations for the onward journey to Antarctica (planned for November 26th).

Punta Arenas, Day 1

With ten of the eleven team members now gathered in Punta Arenas, the GLASS team reconvened in the late morning of November 24th, only a few hours after the group of eight had landed, to review their cold-weather gear. This equipment is essential for operating safely in Antarctica, and the elite guides from Antarctic Logistics and Expeditions (ALE) methodically checked and re-checked every item to ensure the team was properly outfitted for the conditions ahead.

Once the gear inspections were complete, ALE led a series of briefings outlining the itinerary and key milestones for the final 40 hours before the planned departure to Antarctica. It was a full and productive day, capped with a team dinner that marked the first moment of true pause since the journey began. That night, the team finally had the chance to settle in and get a full night's rest—much needed before the work to come.

Punta Arenas, Day 2

Twenty-four hours after the Caltech/JPL team arrived in Punta Arenas—and just thirty hours before the planned departure to Antarctica—Thatcher Chamberlin, the final member of the GLASS field team, reached the southern tip of South America after his own multi-day journey. Early that morning, he completed his gear check, and soon after, he and the rest of the team brought their duffels to ALE for check-in ahead of the next day's flight. With only the essentials kept aside for the day and the clothing they would wear on the flight, the team handed over their bags—one of the final logistical steps before departure.

Once all gear was staged for loading, the group gathered to review the project's scientific objectives, outline priorities for the first days on the continent, and share one last meal together in South America.

With stomachs full, the team stepped outside to watch the final sunset they would see for the next seventeen days. Afterward, the GLASS team retired for the night, ready for the transition to Antarctica to begin.