Millie Spencer

Millie Spencer and Emma Tyrrell: New York Times Article "How Do You Measure Snow From Space? First, Climb a Mountain."

Gabriela Rocha Sales — Tue, 24 Mar 2026 15:12:03 +0000

Millie Spencer and Emma Tyrrell: New York Times Article "How Do You Measure Snow From Space? First, Climb a Mountain." Gabriela Rocha Sales Tue, 03/24/2026 - 09:12

Article copied for archival purposes.

How Do You Measure Snow From Space? First, Climb a Mountain.

A new satellite could transform how water is studied worldwide. But to help unlock its capabilities, scientists first needed to take critical measurements on a mountaintop.

By Sachi Kitajima Mulkey

Photographs and Video by Nina Riggio

Sachi Kitajima Mulkey and Nina Riggio reported from high in the Colorado Rockies alongside a team of scientists on skis.

March 24, 2026

At 4:30 a.m. on a recent Wednesday, three alpine scientists arose from fitful sleep in a chilly research lab in the Colorado mountains, 11,500 feet above sea level. They drank some grainy coffee, strapped into their skis and headed out into the moonlight, dragging a sled loaded with gear.

They had a satellite to meet.

The scientists were on an unusual mission. They needed to measure the depth of the snow at a particular mountaintop location just as a new satellite passed directly overhead. That satellite, equipped with powerful radar, has the potential to be the first one capable of estimating how much water is on the ground, in the form of fallen snow, from outer space.

It would be an extraordinary technological milestone, providing global data on snowpack, precipitation and how much water might be available to feed rivers and reservoirs downstream in spring and summer. But first, the satellite would need to be calibrated.

And one of the most accurate ways to do it is to be physically present on the mountain to measure the snow under the exact same conditions, and at the exact same time, that the satellite does. Other scientists are doing similar things around the world.

Precise timing matters. Snow changes quickly and the satellite passes over the same spot only once every 12 days.

So with hearts pounding from the thin alpine air the three skied out onto moonlit snow. Two of them towed the sled, equipped with a small portable radar that is capable of measuring the snow’s depth and density simply by dragging it back and forth across the mountainside.

“Only 4 centimeters deep here!” one of the scientists, Emma Tyrrell, called out. She was leading the project as part of her Ph.D. at the 91��Ҹ� and the Institute of Arctic and Alpine 91��Ҹ�. At the back of the sled, helping her pull it, was Arielle Koshkin, a postdoctoral researcher in the same lab, who made a note of the measurement.

For two hours, Ms. Tyrrell and Dr. Koshkin skied back and forth in precise zigzags across the slope of the ridgeline, pulling the radar with them and plunging a ruler into the snow every few feet. Somewhere, invisibly above them, the satellite charted its own path across the sky.

The satellite, known as NISAR, was launched last summer by National Aeronautics and Space Administration and the Indian Space 91��Ҹ� Organization. The satellite’s capabilities are the closest humans have come to measuring water content in snow across vast regions, from space, the holy grail of snow science.

The new technology comes at a critical time. As the world warms, snow is vanishing across many parts of the planet. That includes Western United States, which is currently undergoing a record snow drought. In states including Colorado and Utah, the snowpack is the lowest since comprehensive modern recording began, 40 years ago. That’s a problem because these states rely on snow melt for up to 80 percent of their water.

Snowpack, Ms. Tyrrell said, acts like a frozen water tower, storing and releasing water that then gets used by communities and farms downstream throughout the year. She paused to gesture across the mountain peaks, where the snow was visibly patchy and thin.

The area she was working, known as Niwot Ridge, would typically be blanketed in a thick layer of snow this time of year. The area is part of a watershed that provides a third of the water needed by the city of 91��Ҹ�, which was visible that morning, some 25 miles away, as cluster of twinkling lights.

The warming world will doubtlessly transform Colorado, but because of the state’s high elevation there’s uncertainty about precisely how that might play out, Dr. Koshkin said, speaking as she helped Ms. Tyrrell adjust a GPS sensor on the top of the sled. Some precipitation might fall as rain instead of snow, but rain doesn’t remain stored on the mountainside to steadily provide meltwater later in the year. She also said the swings between good and bad snow years are likely to become more drastic.

The sun had started to rise, tinting the mountains scarlet. Several dozen yards away, Millie Spencer, a Ph.D. candidate in the same research group helping out on the day’s mission, was digging a snow pit with a shovel.

This old-school approach remains the gold standard for accurate data on snow. Even when working with modern technologies, like the sled radar, scientists often take analog measurements from snow pits at the same time.

Water managers still rely on long-term records from manual snow measurements to predict how much water to expect from snow each year, from which they create complex forecasting 91��Ҹ� that patch together different kinds of data. Perhaps most important of these is a large federally run network of snow-weighing sensors that take daily measurements across Western states.

But these sources capture only conditions at a single, isolated point. That’s a problem, because snow can vary significantly across even a short area. And as snow vanishes from the places it used to fall, scientists and water managers say these methods will become less reliable.

The new satellite has some important caveats. It can’t measure snow in densely forested areas, or if the snow becomes too wet. And the satellite’s radar doesn’t always strike Earth at an optimal angle for snow measurements.

The problem is that it wasn’t designed or intended to measure snow, said Jack Tarricone, a scientist at the University of Maryland and NASA. The original mission, first proposed more than two decades ago, was to monitor crops and a variety of other Earth systems like natural disasters, tectonic activity and glaciers.

While the new satellite may be no silver bullet, it’s the best chance scientists have had to measure snow on a wide scale. 91��Ҹ�ers at universities and federal agencies alike said they had spent years anticipating the satellite and preparing for its launch.

Now, the clock is ticking. Satellites often stay up well past their intended life spans, but the snow-measuring radar on this one is planned to operate for only three years.

That’s one reason Ms. Tyrrell felt urgency to do these calibration measurements now. Other teams of scientists are also taking measurements at other locations around the world, using a variety of different techniques, to give the satellite the best chance of being accurately calibrated against differing locations and geographical conditions.

Some are flying helicopters and drones with laser scanning devices, other are using radars like Ms. Tyrrell. Each method has pros and cons, but for all its scientific benefits, dragging a sled is certainly hard and slow going.

After several hours, around 7:30 a.m., Ms. Tyrrell and Dr. Koshkin started wrapping up for the day. The satellite had moved on.

They dragged their radar sled back toward the mountainside lab while Ms. Spencer, still working on her snow pit, struggled to examine lumps of snow crystals with a magnifying glass. The task was made nearly impossible by the ribbons of sleet pelting her face.

Back at the shed, Ms. Tyrrell unzipped the cloth covering over the radar and spotted a problem. Snow had somehow gotten onto the device. Worse, one of its many wires had become unplugged.

But there was nothing to be done. It was probably fine, Dr. Koshkin reassured her. The device was made for snow, after all. And most likely the wire fell out as they hauled it indoors.

Next would come a harrowing 45-minute drive back down the mountain in an open-air vehicle with caterpillar treads. Fully checking her data would have to wait until she was back in 91��Ҹ�. Either way, she said she intended to try again when the satellite comes back in a couple weeks, as long as the snow doesn’t melt in the meantime.

That’s just the nature of studying snow. “There’s only so much you can control,” she said. “We have to work with what we’ve got.”

Sachi Kitajima Mulkey covers climate and the environment for The Times.

A new satellite could transform how water is studied worldwide. But to help unlock its capabilities, scientists first needed to take critical measurements on a mountaintop.

By Sachi Kitajima Mulkey

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PhD candidate Millie Spencer featured in Denver Gazette article on Colorado Glaciers

Gabriela Rocha Sales — Mon, 08 Dec 2025 20:49:14 +0000

PhD candidate Millie Spencer featured in Denver Gazette article on Colorado Glaciers Gabriela Rocha Sales Mon, 12/08/2025 - 13:49

Science communication has long been a passion of mine, and I am so grateful to have the opportunity to share a bit of my work, my perspective on glacier retreat and its environmental and sociocultural impacts with Seth at the Denver Gazette. While we as hydrologists so often focus on the scientific impacts on glacier melt—be it streamflow reduction, habitat loss, sea level rise, or increasing temperatures—glacier disappearance can also impact a community's sense of place and identity. It was a pleasure to chat with Seth and share what I've learned about how those of us living downstream of glaciers are shaped by these stoic features on our landscape. Whether on family hikes or ski days in basins carved by long-gone glaciers or simply driving west from SEEC on Colorado Ave. and looking up at Arapaho glacier, part of our identity as Colorado residents is shaped by our proximity to ice of past and present. As I shared with Seth, there's a sense of grief and nostalgia that comes from knowing that glaciers we have the pleasure of visiting will soon disappear, and that future generations will only know the mark they left on our landscapes and memories.

Spencer (center) with fellow Geography PhD student Sydney Carr (left) after conducting drone flights over Arapaho glacier last summer.

Read the article here: https://www.denvergazette.com/2025/09/28/the-legacy-and-loss-of-colorados-once-mighty-glaciers/

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CUAHSI August e-Newsletter Community Guest Spotlight with Millie Spencer

Gabriela Rocha Sales — Mon, 18 Aug 2025 14:04:49 +0000

CUAHSI August e-Newsletter Community Guest Spotlight with Millie Spencer Gabriela Rocha Sales Mon, 08/18/2025 - 08:04

Copied for archival purposes from Cuahsi.org

August e-Newsletter Community Guest Spotlight with Millie Spencer

Posted Aug 12, 2025

Combining Local Knowledge and Western Sciences to Analyze Glacier Retreat and Water Security in South-Central Chile

Millie Spencer, PhD Candidate, 91��Ҹ�, 91��Ҹ�, CUAHSI Pathfinder Awardee 2024

The CUAHSI Pathfinder Award enabled me to travel throughout south-central Chile for five months, where I conducted uncrewed aerial vehicle (UAV) surveys of volcanic glaciers, and interviews with individuals living downstream of the glaciers. My interdisciplinary project aims to create a more complete picture of glacier retreat and its downstream impacts on water security, when compared to conventional hydrological studies that rely exclusively on remote sensing and computer modeling.

During peak melt season, from February-March 2025, I hiked several volcanoes in south-central Chile and flew UAV to measure the current surface area of glaciers. In addition to updating regional glacier inventories, this fieldwork enabled me to identify unique processes that are not discussed in local scientific literature to date, such as the presence of undocumented debris-covered glaciers and the influence of volcanic eruptions on glacier melt. I plan to integrate my UAV measurements in a hydro-glaciological model to forecast how historic and continued glacier retreat will impact the timing and volume of water availability downstream.

Once snowfall began, I shifted my focus to interviewing community members living downstream of these glaciers. I interviewed people ranging from Indigenous elders to city water managers and ecotourism guides. My questions sought to illuminate their perspectives of glacier retreat and hydroclimatic change in the region. While some alpine mountain guides shared perspectives on glacier change, the majority of those interviewed did not have personal experience with glaciers. Instead, most interview subjects spoke on broader environmental and hydrological change. Interviewees agreed that water insecurity is growing in the region, in part due to accelerating glacier retreat and less predictable precipitation, but also due to population growth and growing water demands of tree plantations. Many interviewees spoke on concerns surrounding the infiltration of non-native pine and eucalyptus species in native Araucaria (or pewen, in the Mapuche language of Mapundungun) forests. Others shared observations that snow fell less frequently and stuck around for less time. Smaller rural community members shared experiences of historic water sources (mainly springs near their homes) drying up, forcing them to begin purchasing water from municipalities or water tankers for the first time.

In essence, my interviews illuminated that observations of hydrological change were abundant, while those specific to glacier change were scarce. This finding is helpful to inform how future scientific studies, including my own work, should better frame glacier change in the context of water security. Rather than simply reporting rates of glacier retreat in technical units and jargon, researchers should frame glacier change in the context of how it impacts the timing and volume of water availability to communities downstream.

I am enormously grateful to the CUAHSI Pathfinder Award for enabling me to conduct this research, and look forward to sharing further results soon!

Combining Local Knowledge and Western Sciences to Analyze Glacier Retreat and Water Security in South-Central Chile

Millie Spencer, PhD Candidate, 91��Ҹ�, 91��Ҹ�, CUAHSI Pathfinder Awardee 2024

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Millie Spencer Studying Glacier Retreat in Chile

Gabriela Rocha Sales — Mon, 28 Apr 2025 19:35:36 +0000

Millie Spencer Studying Glacier Retreat in Chile Gabriela Rocha Sales Mon, 04/28/2025 - 13:35

My name is Millie Spencer, and I am a 3rd year PhD candidate in the Geography Department. I am currently on a Fulbright Award studying glacier retreat and its downstream impacts in south-central Chile. Hosted jointly by the University of Chile’s Civil Engineering Department and Indigenous Peoples Program, my work integrates glacier field measurements, glacier-hydrological modeling, and semi-structured interviews with periglacial communities. This approach seeks to bridge scientific methods with Indigenous and local knowledge, recognizing community memory as a critical resource for understanding climate change and informing adaptation strategies.

The first month and a half of my time here in Chile has been a whirlwind. The season to safely and accurately measure glaciers here in Chile is February-April, so I am working hard to hike to as many glaciers as possible before winter begins in full force. Accompanied by my generous colleagues here in Chile, we are hiking a chain of stratovolcanoes in south-central Chile to fly uncrewed aerial vehicles (UAV) and build digital elevation 91��Ҹ� of the glaciers. These 91��Ҹ� enable us to compute the volume loss of the glaciers over time.

In March, I spent two days camping at the base of Glaciar Nevado with my colleague Robert Clasings. The hike to Glaciar Nevado is an arduous 8 miles up volcanic sand dunes and lahars. However, our gorgeous camp near a waterfall with a view of the glacier above made the effort worthwhile. This mission enabled us to map the entire glacier, including a debris covered portion that was previously unidentified by scientists.

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Millie Spencer awarded Fulbright Fellowship 2024-2025

Anonymous — Tue, 07 May 2024 16:48:56 +0000

Millie Spencer awarded Fulbright Fellowship 2024-2025 Anonymous (not verified) Tue, 05/07/2024 - 10:48

Millie Spencer has been awarded the 2024-2025 Fulbright-Nehru 91��Ҹ� Fellowship.

She is currently doing field work in Concepción, Chile, analyzing glacier retreat and its impacts on downstream communities in south-central Chile.

The Chile Fulbright Science Initiative will enable her to expand her existing research in Chile further south to the region of Araucanía, where she plans to work with Mapuche-Pehuenche communities to document oral histories of glacier retreat and hydrological change, and illuminate how water insecurity disproportionately impacts Indigenous peoples.

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Welcome to Our Fall 2022 Graduate Students

Anonymous — Wed, 07 Dec 2022 21:52:27 +0000

Welcome to Our Fall 2022 Graduate Students Anonymous (not verified) Wed, 12/07/2022 - 14:52

Please join us in welcoming our incoming graduates for Fall 2022!

Back row: Millie Spenser, Priscilla (Pris) Corbett, Drolma Gadou, Briana Prado, Emma Barrett, Denise Mondragon, Mia Murray, Taylor O’Brien, Nathan Korinek, Ethan Carr; Middle row: Alaric Kothapally, Michele Lissoni, Aja Procita, Nic Tarasewicz, Patrick (Pat) Saylor, Isaiah Lyons-Galante; Front row: Sam Fixler, Jiacheng (Raymond) Zhou; Insert: Jill Adler Grano

Featured Updates

Isaiah Lyons-Galante

Originally from Boston, I went to Yale for a bachelor's degree in physics and mechanical engineering. With an interest in sustainable development internationally, I found my way to Kenya where I worked for 6 years with a start-up developing renewable energy projects in rural, off-grid areas. There, I learned about the power of remote sensing, GIS, and machine learning to study remote areas and make data-driven decisions. This brought me to CU in the Geography department to dive into geospatial data science, working with Morteza Karimzadeh in his GeoHuman AI Lab. I am interested in finding ways to apply statistics and deep learning 91��Ҹ� to remotely-sensed data to study remote regions of the world and to understand which factors lead to economic growth and well-being in harmony with the environment.

Nic Tarasewicz

I was raised in the San Juan Mountains in southwestern Colorado, which started my interest in alpine environments. I completed my undergraduate degree in Geography from the University of Denver, and my Master’s in Physical Geography and Ecosystem Science at Lund University, Sweden. While there, I developed a novel composite indicator representing the impact of modeled forest management practices on ecosystem services. My research interests center around understanding climate and anthropogenic impacts on mountain ecosystem services through combining empirical measurements and modeling. I am working with Peter Blanken on INSTAAR’s Ecosystem Resilience Project, led by Keith Musselman, aiming to define and project climate-change refugia in the Colorado Front Range. My hobbies include spending time outdoors, performance art, and playing board games with friends.

Ethan Carr

Growing up my greatest memories we’re visiting national parks with my family and learning about plants, animals, and the environment. As I grew up I never lost that passion and knew I wanted to make a career around being outdoors and learning.

I received my Bachelors of Science in Physical Geography from the United States Military Academy, where I was a four year varsity athlete. Upon graduation I was commissioned as a Second Lieutenant in the Infantry. I recently changed career paths and knew that I wanted to make a difference in the world. I decided to combine my passion for nature, especially the Arctic, and my goals to make change and pursue a career in the natural sciences. The CU Geography department seemed like the perfect place to begin this journey.

I hope to focus in Glaciology and Climate change specifically in Greenland. Upon finishing my masters I wish to pursue a PhD in a similar field.

Briana Prado

My name is Briana Prado, I am from San Diego, California, and studied Chemistry and Earth Science at UC Santa Cruz. I will be studying geochemistry and chemical weathering in the McMurdo Dry Valleys under Dr. Melissa Diaz. I am super stoked to be in 91��Ҹ�, CO, and spend time outside hiking and biking and experiencing a true winter.

This past summer I sharpened my U.S geography skills while cycling across the country from Baltimore MD to San Francisco, CA with a group of 23 cyclists to raise funds for a cancer charity. The tour took us through 11 different states and 7 national parks over 70 days. We transverse mountain ranges such as the Appalachians, Rockies, and Sierra Nevada Mountains, and crossed the Mississippi, Missouri, and Colorado Rivers.

Fun Fact: I visited CU 91��Ҹ� for the first time during the bike ride when we had a rest day in 91��Ҹ�. This was the day before biked before heading into Estes Park through highway 34 and then biking into Rocky Mountain National Park and climbing trail ridge!

I had so much fun that I would 100% do it again. These days you’ll probably catch me riding my red single-speed bike called Tessie around campus.

Photos from Briana's Cross-country Cycling Trip

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