How can GPS monitor glacier ice melt? A proof-of-concept field test in Antarctica


By: Dr. Alison Banwell

Photo by Seebany Datta-Barua

Antarctica is the world’s largest ice sheet, spanning an area comparable to the entire United States reaching a staggering thickness of up to 3 miles at its center. Consequently, visitors to the South Pole often experience altitude sickness due to the extreme elevation. Additionally, Antarctica is renowned for its harsh climate, with temperatures plummeting to as low as -80°C (-112°F) during the winter months. However, at low elevations around Antarctica’s coast, especially on its ice shelves, which are floating extensions of the continent’s glaciers on land, snow and ice are melting at accelerating rates.

McMurdo, Antarctica | Photo by Ali Banwell

As well as being a member of POW’s Science Alliance, I am a glaciologist and Research Scientist at the University of Colorado Boulder. Much of my current research focuses on Antarctica’s ice shelves, which surround about 75% of the continent and are different from the sea ice that also surrounds Antarctica. Sea ice is frozen ocean, while ice shelves are glacier ice spilling off the land onto the sea. They are extremely important for Antarctica’s overall health as they provide structural support through a buttressing force, which holds back the land-based glacier ice from otherwise flowing rapidly into the oceans and contributing to sea-level rise. However, Antarctica’s ice shelves are thinning in response to both surface melt due to rising air temperatures and melting on their undersides due to warming ocean water. In turn, this means that ice shelves are weakening, diminishing their important ability to hold back inland glacier ice. The scary reality is that if all of Antarctica’s ice were to end up in our oceans, global sea levels could rise by about 190 feet, and ice shelves are currently an important guard against this.  

Fieldwork on the McMurdo Ice Shelf, November – December 2023. 

Unlike my last Antarctica field expedition in 2022, which was based on the Antarctic Peninsula, closest to South America, this time we worked out of the U.S. McMurdo Station on Ross Island, East Antarctica. To get to McMurdo Station, my colleague Prof. Seebany Datta-Barua and I took a 5-hour flight on a US Air Force C-17 Globemaster III from Christchurch, New Zealand, in November 2023, the beginning of Antarctica’s austral summer. These jets, which can weigh up to 300 thousand US pounds when full of people and/or cargo, land on the floating glacier ice closest to McMurdo Station—the McMurdo Ice Shelf—which thankfully is just thick enough (about 250 m) to support their gigantic weights upon landing. 

The town of McMurdo as seen from Hut Point. | Photo by Ali Banwell

The McMurdo Ice Shelf, which is also where we carried out our National Science Foundation (NSF) funded fieldwork, is in the northwest corner of Antarctica’s largest ice shelf, the Ross Ice Shelf, which is almost as large as the state of Texas. McMurdo Station, which is run by the NSF, is the largest research station in Antarctica, hosting a population of more than 1,000 people in the austral summer (October to February), including scientists and support staff.  However, the population decreases to only around 100 people during the harsh Antarctic winter months. McMurdo Station is like a small town and comprises a variety of facilities, including science laboratories, dormitories, a galley, administrative buildings, a fire station, a gas station, a wastewater management plant, three gyms, two bars, a coffee shop, a chapel, a barber shop, a helicopter pad and hanger, and a harbor. The mean annual temperature is 0°F, but temperatures may reach 46°F in summer and -58°F in winter. Despite the cold, McMurdo’s range of facilities means it’s a very civilized place to be based for a couple of months of fieldwork; luxurious in fact, especially when compared to weeks of camping on the ice during a field expedition! From McMurdo, there are also fantastic views of Mt Erebus, the Earth’s most southerly volcano. Unfortunately, however, McMurdo Station is at the end of a very long fjord, the McMurdo Sound, which is usually full of sea ice until late summer, so wildlife, including Antarctica’s most famous residents, penguins, is sparse. So much so, that on this most recent trip, I did not see a single penguin!

How can GPS systems be used to monitor Antarctica’s melting glacier ice?

Satellites in the Global Positioning System (GPS), which is one of several Global Navigation Satellite Systems (GNSS), are continuously transmitting signals toward Earth. While many people may be familiar with using GPS for positioning and navigation, for example, while backcountry skiing, hiking or driving, it is also possible to use these signals to monitor the Earth’s surface environment, including glaciers. Ice and snow surfaces are continuously awash with the radio signals broadcast from GPS satellites. When the radio signal from these satellites bounces off different Earth surfaces, it can be picked up by an antenna, and the data stored, so with a specialized receiver, GPS acts as a form of radar. This radar transmitter is free, covers the globe, is always on, and is unaffected by clouds, precipitation or other weather conditions. 

Towers with mounted instruments | Photo by Ali Banwell

The aim of our field project on the McMurdo Ice Shelf in November and December 2023 was to develop and provide proof-of-concept for a new technique called ‘GPS-reflectometry’ (also known as ‘GNSS-reflectometry’). This technique was designed to detect GPS signal reflections from glaciated surfaces, with the goal of understanding how the reflected signal changes depending on surface type, including powdery snow, wet snow, ice, meltwater or a combination of various surface types. This innovative method of using GPS to detect different surface types on glaciated surfaces holds significant promise for monitoring surface melt conditions across Antarctica, key observations that are currently lacking. Although some climate models attempt to simulate surface melt, and some types of satellite data products can be used to infer where meltwater is present in Antarctica, very few observations of surface melt currently exist, but are vital for testing and improving models and satellite data.

For our experiments on the McMurdo Ice Shelf, we mounted two GPS antennas at the top of a 10-meter tower; one oriented upwards for positioning purposes, and another directed downwards to capture reflections from the glacier surface below. To ensure the accuracy of our interpretations of the GPS reflections from the glacier surface, we supplemented our setup with four security-style cameras on each tower. Additionally, we employed a scanning lidar (radar but using laser light) instrument, which helped us generate a detailed representation of the surface elevation.

Riggers mounting science sensors on the tower with the Mt Erebus volcano pictured in the background | Photo by Ali Banwell

Early results are looking to be very promising, however, we still have a huge amount of field data to process and analyze, as our instruments were collecting over 1 GB of data a minute! We hope that our data will show that GPS-reflectometry is a viable, cheap method to monitor surface melt in many locations over Antarctica’s ice shelves. This is particularly important because as atmospheric and ocean temperatures continue to rise, Antarctica’s ice shelves are predicted to thin, weaken and break up at ever greater rates. This means that Antarctic ice will contribute more to global sea-level rise in the forthcoming decades and centuries. Currently, the world’s second-largest ice sheet, Greenland in the Arctic, is contributing more to sea-level rise than Antarctica, but Antarctica is predicted to overtake Greenland by the end of this century. Current projections indicate that sea levels could rise by one to three feet over this time period; an unsettling prospect given that a three-foot rise could potentially displace approximately 100 million people living in coastal regions.

Why I joined the POW Science Alliance?

Dr. Ali Banwell collecting data on a laptop | Photo by Seebany Datta-Barua

I became a part of the POW Science Alliance driven by a growing frustration stemming from studying the effects of climate change on Earth. Specifically, witnessing the alarming pace at which rising temperatures are melting the planet’s glaciers, alongside a concerning trend in policy towards apathy rather than proactive action. Through my involvement with POW, I am confident that together, as a team, we can achieve a greater impact by advocating for the climate. By supplying climate-related facts to POW, I aim to empower the POW community with a deeper understanding of scientific data, enabling them to effectively communicate this information to their peers. 

Dr. Alison Banwell

Author: Dr. Alison Banwell

Dr. Alison (Ali) Banwell is a glaciologist currently living in Boulder Colorado, but is originally from England UK. She moved to the United States in 2018 for a Research Scientist position at the University of Colorado Boulder, where she is still based. Ali’s research interests revolve around investigating the impact of Earth’s past and future […]