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\DOI{10.5802/crgeos.298}
\datereceived{2025-01-31}
\daterevised{2025-05-18}
\dateaccepted{2025-05-26}
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\dateposted{2025-06-17}
\begin{document}

\begin{noXML}

\TopicFR{G\'eophysique de surface}
\TopicEN{Surface geophysics}


\CDRsetmeta{articletype}{review}

\shortrunauthors

\title{Studying cold regions with ground-penetrating radar: a review}

\alttitle{\'Etude des r\'egions glaciaires et p\'eri-glaciaires par radar
\`a p\'en\'etration de sol : une synth\`ese}

\author{\firstname{Albane} \lastname{Saintenoy}\IsCorresp\CDRorcid{0000-0002-9712-3781}}
\address{CNRS, Universit\'e Paris Saclay, GEOPS, France}
\email[A. Saintenoy]{albane.saintenoy@universite-paris-saclay.fr}

\author{\firstname{Emmanuel} \lastname{L\'eger}\CDRorcid{0000-0001-7669-3622}}
\addressSameAs{1}{CNRS, Universit\'e Paris Saclay, GEOPS, France}
\email[E. L\'eger]{emmanuel.leger@universite-paris-saclay.fr}

\begin{abstract} 
Ground-Penetrating Radar (GPR) provides high-resolution, non-invasive
insights into the subsurface, making it an essential tool for assessing
climate change impacts and managing infrastructure in Arctic and
sub-Arctic environments. This review examines GPR applications in
mapping and characterizing cold-region features to enhance our
understanding of the Critical Zone at high latitudes. Specifically, we
focus on permafrost, including its active layer and embedded ice
structures, as well as glaciers and front moraine, ice sheets, and snow
cover. Furthermore, driven by advancements in miniaturization and
energy efficiency, we extend our review to GPR-based subsurface
exploration on the Moon and Mars, where environmental conditions and
frozen geomorphological structures share similarities with terrestrial
cold regions. Finally, we highlight the interconnection between
hardware and software advancements and the expanding applications of
GPR in cryospheric research.\looseness=-1
\vspace*{-2pt}
\end{abstract}

\begin{altabstract} 
Le radar \`a p\'en\'etration de sol (RPS) offre une imagerie du
sous-sol \`a haute r\'esolution et de mani\`ere non invasive, et est
un outil essentiel pour \'evaluer les impacts du changement climatique
et g\'erer les infrastructures dans les environnements arctiques et
subarctiques. Cet article de synth\`ese examine les applications du RPS
dans la cartographie et la caract\'erisation des milieux des r\'egions
froides afin d'am\'eliorer notre compr\'ehension de cette zone critique
aux hautes latitudes. Nous nous concentrons notamment sur le
perg\'elisol, incluant sa couche active et les structures de glace
qu'il contient, ainsi que sur les glaciers, les moraines frontales,
les calottes glaciaires et la couverture neigeuse. En outre, stimul\'ee
par les progr\`es en miniaturisation et en efficacit\'e
\'energ\'etique, notre revue s'\'etend \`a l'exploration souterraine
de la Lune et de Mars \`a l'aide du RPS, o\`u les conditions
environnementales et les structures g\'eomorphologiques gel\'ees
pr\'esentent des similitudes avec les r\'egions froides terrestres.
Enfin, nous soulignons l'interd\'ependance entre les avanc\'ees
mat\'erielles et logicielles et le d\'eveloppement croissant des
applications du RPS dans les recherches sur la cryosph\`ere.
\end{altabstract} 

\keywords{\kwd{Ground-penetrating radar}
\kwd{Permafrost}
\kwd{Active layer}
\kwd{Glacier}
\kwd{Snow cover}
\kwd{Infrastructures}
\kwd{Planetary exploration}}

\altkeywords{\kwd{Radar \`a p\'en\'etration de sol}
\kwd{Perg\'elisol}
\kwd{Couche active}
\kwd{Glacier}
\kwd{Couverture neigeuse}
\kwd{Infrastructures}
\kwd{Exploration plan\'etaire}}

\maketitle

\twocolumngrid

\end{noXML}

\let\rmmu\upmu

\defcitealias{lonne1996architecture}{ibid.}
\defcitealias{giannakis2015realistic}{ibid.}
\defcitealias{friedt2018acoustic}{ibid.}

\section{Introduction}

Hypothesized since the Third Assessment report of the Intergovernmental
Panel on Climate Change \citep{ipcc1990}, it is now observed that the
thermal anomaly related to climate change is more pronounced at high
latitudes than in the rest of the globe. This gave birth to the terms
``Arctic thermal anomaly'' and ``Arctic amplification'' which are now
widely used in the literature \citep{previdi2021,serreze2009}.  As
warming trends are projected to accelerate by the end of the
century \citep{portner2019}, with varying magnitudes depending on the
selected scenario ({e.g.}, RCP 2.6, RCP 4.6), the fragile thermodynamic
equilibrium of near-surface cold regions will be significantly
affected. These changes will impact water resources and
vegetation \citep{jorgenson2010}, consequently altering key
biogeochemical cycles, such as the nitrogen and carbon
cycles \citep{Petrone2007}.

The effects of climate warming will be evident in various cold-region
features, including permafrost and its active layer, which undergoes
seasonal freeze-thaw cycles, as well as ice wedges, pingos, glaciers
and their associated moraines, and snow cover. These impacts may
manifest as a deepening of the active layer or through more dramatic
geomorphological changes such as landslides, thermokarst
formation \citep{zhirkov2023}, and retrogressive thaw
slumps \citep{Costard2021}. Examining these observable consequences in
cold-region environments can, in turn, serve as a valuable proxy for
quantifying the spatial and temporal extent of climate change impacts.

Near-surface geophysical methods provide a non-destructive means of
investigating the subsurface over large areas in diverse contexts,
contributing to their widespread adoption. In cold-region studies,
electromagnetic (EM) wave-based methods, particularly radar, have been
employed since the 1950s \citep{annan2001}. Over time, radar technology
has advanced from early pulse-based systems to impulse radar and
continuous-wave emissions.

As technology has evolved and applications have broadened, the
terminology for these radar systems has also diversified, encompassing
terms such as ``deep-looking radar'', ``ice-penetrating radar'', ``ice
radar'', ``ice-sounding radar'', ``snow radar'', ``impulse radar'',
``(phase-sensitive) and (autonomous-phase-sensitive) radio echo
sounder'' and both ``real'' and ``synthetic aperture radar.'' The
classification of these terms in the context of cryospheric research
has been addressed by \citet{schlegel2022towards}. In this paper, we
focus on Ground-Penetrating Radar (GPR), including both impulse and
continuous-wave systems, while excluding radio echo sounders. For a
more detailed discussion of the latter, we refer readers to the review
by \citet{schroeder2020five}.

The GPR literature already includes review studies focused on cold
region applications \citep[e.g.,][]{woodward2007,arcone2009}.
Here, we provide an up-to-date review of
cold-regions GPR research that goes beyond the previous review papers
on the topic, covering a quite large panel of different applications. 
Following a brief overview of the physical principles of GPR, we
categorize studies based on cold-region features, beginning with
permafrost and active-layer investigations, followed by glacier and ice
sheet studies, snowpack assessments, and infrastructure analyses. We
then extend the discussion to recent extraterrestrial subsurface
explorations. The final section highlights past, present, and future
technological breakthroughs that have established and will continue to
establish GPR as an indispensable tool for cold-region research.



\section{GPR principles 101}

A substantial body of literature explores GPR applications, technical
advancements, and algorithmic developments, with numerous examples
across various contexts
\citep[e.g.][]{slob2010,Jol2009,forte2017review,neal2004ground,knight2001ground,annan2003ground}. 
Readers of French-language texts may refer to PhD
manuscripts \citep{tillard1991, leparoux1997,
saintenoy1998,aboudourib2020,brighi2024}.

GPR is a geophysical technique based on the propagation of EM waves and
is therefore sensitive to the dielectric permittivity (which influences
EM wave velocity), electrical resistivity (which affects wave
attenuation), and magnetic susceptibility of the medium through which
the wave travels. The system operates with a transmitting antenna (Tx)
that emits EM waves at frequencies ranging from 1~MHz to 4.5~GHz into
the ground. These waves interact with subsurface structures, undergoing
diffraction and reflection before being recorded by the receiving
antenna (Rx). The transmitted frequency can be either fixed (with a
certain bandwidth around the center frequency) or modulated, depending
on the specific application. The recorded signals are then analysed in
terms of time and amplitude to infer subsurface properties.

Different geometries of acquisition between Tx and Rx can be set up,
using a fixed offset between them (giving mono-offset profiles), or
varying ones (to obtain multi-offset profiles),  with antennas both at
the surface (reflection profiles) or in boreholes (transmission
profiles). For reflection profiles, the antennas can be either
on-ground or off-ground.  Fixed pair of antenna can be used for
monitoring EM property changes such as those implied during water
infiltration \citep{Saintenoy2008,Leger2014WRR,leger2020evaluating},
freezing-thawing cycles \citep{leger2023brief}, or snow layer
transformation \citep{griessinger2018}.  

The EM wave velocity propagating in the different geological media
ranges from 0.3~m/ns in air to approximately 0.03~m/ns in fresh water.
This order of magnitude difference explains the success of this method
for hydrological applications \citep[see e.g.\ the review
from][]{klotzsche2018measuring}. The aforementioned value
intervals permit the calculation of the wavelengths of a GPR EM wave,
which range from 6~mm in water at the upper frequency limit
(disregarding dispersion effects) to 300~m in air at the lower limit. 
Different velocity analysis are applied depending of the GPR data, the
most common method being the analysis of diffraction hyperbolas on
mono-offset profiles \citep{ristic2009, dou2016a, liu2023} allowing to
convert time to distance through Kirchoff or Stolt
migrations \citep{moran2000multidimensional,stolt1985migration}.

In its most common applications in cold regions, frequencies range from
2~MHz to 2~GHz for the \mbox{detection} of targets buried in media with
velocities ranging from~0.05 to approximately~0.2 m/ns (the range of
velocity is very much depending on if water is present in the pores of
the sounded medium and its temperature). In these instances, the
wavelength range is reduced to 0.1--100~m and the corresponding
Fresnel zone, being roughly proportional to the quarter of the
wavelength, gives the resolution.  These rough calculations illustrate
the range of heterogeneities typically investigated by GPR measurements
in cold regions ranging from centimetric to multi-decametric scales.
This is well illustrated by two studies within the edges of this 
range: \citet{arcone2009} carried GPR profiles in Antarctica with 3-MHz
system and retrieved migrated profiles with a 2000~m depth of
penetration. On the other side of the range, very thin layers (e.g.\ a
1~mm layer of ice within a thick layer of snow) were resolved through
EM reflection amplitude enhancements \citep{widess1973} and exploited
by \citet{brandt2009} to evaluate heterogeneities in firn (ice that is
intermediate between snow and glacial ice).

Governed by the physics of EM waves, the penetration depth of a given
radar system is primarily determined by the intrinsic attenuation
properties of the medium it traverses. Signal loss is influenced by
electrical resistivity, dielectric and magnetic relaxation processes,
and the presence of multiple scatterers. For instance, high signal
attenuation occurs in the presence of mineralized liquid water or/and
clay particles within the thawed active layer, as well as in materials
with small scatterers such as rock deposits in moraines or gas bubbles
in ice.  However, beyond scattering losses, EM wave attenuation is
significantly lower in ice and frozen sediments compared to unfrozen
materials. This reduction in attenuation makes such environments ideal
for detecting signals from interfaces with minimal reflection
coefficients, as demonstrated in various contexts in the following
sections.

\section{Applications in cold regions}

\subsection{Permafrost and intra-permafrost structure studies}

Cold regions, characterized by mean annual temperatures close to or
well below zero, present continuous, discontinuous, or sporadic
permafrost associated with a seasonally thawing active layer, as well
as distinct frozen features such as ice wedges. Additionally, these
regions host large thawed features, including taliks and thermokarsts.
All these features were the subjects of numerous geophysical studies
\citep[e.g.][]{hauck2013}. Among them, we will focus on those using GPR.

The active layer, which annually thaws and freezes, is the object of
great attention as its properties (thickness, temperature and
liquid/solid water content) and their time and space variations are
proxies for the permafrost thermal state and integrity, the near
surface hydrodynamic (covering the water availability and as such, the
plant--soil-micro and macro-organisms interactions with atmospheric
boundary conditions), and the potentiality of CO$_2$ and CH$_4$
releases \citep{torn2025large}.  In this case, the information brought
by GPR for quantifying the active layer physical state concern mainly
its thickness \citep{nakano2008,cao2017spatial,chen2016ground} and
stratigraphy \citep{gusmeroli2015active}, as well as its solid/liquid
water and soil and gas relative
proportions \citep{gacitua2012estimations,wollschlager2010multi,westermann2010}.

Due to its high heat capacity relative to most sediments and its low
thermal conductivity, liquid water significantly influences permafrost
thermal degradation and, consequently, active layer thickness. This
effect has been investigated in various
contexts \citep{bradford2005measuring,brosten2009,leger2023syrdakh,terry2020seasonal,krutskikh2023}, particularly in relation to water bodies such as streams and rivers. These studies aim to identify the key factors driving permafrost degradation, with the goal of improving predictions and mitigation strategies.

In Siberian permafrost studies, GPR profiles, combined with Unmanned
Aerial Vehicle (UAV) data and electrical resistivity tomography
(ERT) \citep{leger2023syrdakh}, have been used to infer the thermal
state of permafrost near a small river in Yakutia (Eastern Siberia).
This analysis highlighted the complex interactions between solar
orientation, vegetation type, river dynamics, and subsurface massive
ice bodies, all of which influence active layer thickness and
river-induced thermal effects on permafrost.

For larger water bodies, towed floating GPR systems have been employed,
as demonstrated by \mbox{\citet{bradford2005measuring},} who obtained a clear,
\mbox{continuous} image of the permafrost boundary both beneath and adjacent
to a stream. Additionally, a more advanced approach integrating UAV and
remote sensing techniques was conducted by \citet{krutskikh2023} to
study Palsa Mire features. Detailed vegetation mapping was correlated
with GPR-derived permafrost table depth, enabling a more precise
geomorphological interpretation and delineation of lateral permafrost
degradation.

Since GPR data are typically collected and visualized as 2D transects,
the representation of complex 3D geological structures can be
misleading. To address this limitation, several studies have employed
3D mapping techniques by meshing multiple 2D GPR
surveys \citep{brosten2009,terry2020seasonal}. \citet{brosten2009}
demonstrated the application of 3D GPR to map seasonal thaw thickness
in different Arctic stream environments, showing that maximum thaw
depth is influenced by subsurface lithology and distinct thermal
processes. Similarly, \citet{terry2020seasonal} combined GPR with
nuclear magnetic resonance (NMR) and temperature sensing to identify a
perennial suprapermafrost groundwater flow system beneath an Arctic
aufeis field---large accumulations of ice common to Arctic river
floodplains---supporting an extensive lateral talik.

Beyond permafrost studies, GPR has been widely used to investigate
large, non-horizontal ice structures such as pingos, ice-wedge
polygons, and massive ice bodies from glacial
relics \citep{yoshikawa2006,brandt2007,ross2005ground}. In Northern
Alaska, near Fairbanks, GPR demonstrated sufficient resolution to
delineate the internal structure and boundaries of a pingo using a
low-frequency (&lt;80 MHz) system \citep{yoshikawa2006}. The choice of GPR
over other geophysical methods was primarily driven by its portability,
ease of use, and deep penetration capability for ice characterization.
A more detailed mapping of the internal structure of two open-system
pingos in Svalbard was conducted by \citet{ross2005ground}, who used
GPR signal contrasts to infer variations in ice chemistry, as well as
alternating layers of shale and ice, reflecting the pingos' formation
within weak Jurassic shales. Similarly, GPR has been employed to image
the internal structure of a relic glacier in Svalbard at varying
resolutions \citep{brandt2007}. The study compared results from
different commercial GPR systems using antennas ranging from 200 to 800
MHz to effectively map the extent of buried ice and sediments.

Ice wedges, often forming polygonal networks, are iconic permafrost
features in the Arctic and have been extensively studied as indicators
of permafrost
degradation \citep{jorgenson2022rapid,liljedahl2016pan,grant2017mathematical}. GPR has proven to be a valuable tool for detecting and refining the geometry and spatial distribution of ice-wedge networks \citep{Watanabe2013,leger2017,harris2025using}.
However, their detection is not always straightforward, and the
combined use of GPR with ERT can improve characterization, as
demonstrated by \citet{leger2017}. The integration of two-dimensional
and three-dimensional GPR surveys, along with ground thermal monitoring
and acceleration measurements, has provided deeper insights into the
factors influencing ice- and soil-wedge formation under present
climatic conditions in the Kapp Linn\'e region,
Svalbard \citep{Watanabe2013}.

To conclude the discussion on GPR applications in permafrost studies,
it is essential to address high-mountain permafrost. Over the past two
decades, permafrost and other cryosols have attracted increasing
interest, driven by expanding urbanization in mountainous
regions \citep{ehrlich2021population} and the accelerating impacts of
climate change. This issue has direct societal relevance, as it affects
slope stability \citep{magnin2023rockfall} and can trigger extreme
events such as massive rock avalanches and large-scale solifluction
flows---exemplified by the catastrophic event in India's Himalayan
Uttarakhand state in 2021 \citep{verma2022}. Despite the challenges
posed by the accessibility of high-altitude permafrost sites, GPR has
been successfully tested in conjunction with seismic refraction
tomography and ERT to constrain subsurface models for estimating ice
and water content. A notable example is the study
by \citet{steiner2021} in the Austrian Alps, where these geophysical
techniques were integrated to improve the characterization of
permafrost distribution and dynamics.

\subsection{Glacier and ice sheet investigations} 

Glaciers and ice sheets are among the most suitable targets for GPR, as
signal propagation is facilitated by the high electrical resistivity of
ice, which can be considered a near-lossless medium. As opposed to
permafrost, no dispersive active layer is above the ice body leading to
excellent depths of penetration. However, this advantage is mitigated
in the presence of sea ice or trapped brine, which can cause
significant signal attenuation \citep{blindow1994central}. When saline
inclusions are absent, GPR has been widely used to measure ice
thickness \citep{cook1960proposed,Evans1963,Arcone1996,saintenoy2013deriving}, 
map internal stratigraphy \citep{arcone2004stratigraphic}, and assess
basal conditions \citep{saintenoy2013deriving}, such as the presence of
subglacial water \citep{hart2015englacial}. These studies have taken on
increasing urgency in light of the ongoing decline in glacier volume
due to climate warming \citep{shannon2019global}, which contributes
directly to rising sea levels.

Since the 1960s, Radio Echo Sounding has proven to be a powerful tool
for obtaining extensive ice thickness measurements, particularly
through aerial surveys \citep{cook1960proposed,Evans1963}. GPR
measurements followed later, with significant advancements in the
1990s \citep{Arcone1996}. In 2001, a research team participated in a
study of a small glacier in the tropical Andes, initially employing
refraction seismic data before conducting a 50 MHz PulseEkko survey,
which provided higher spatial resolution in thickness estimation than
seismic methods \citep{ramirez2001}. In Europe, extensive GPR surveys
were conducted on the Austre Lovenbreen glacier (Svalbard), leading to
the derivation of a digital elevation model of the underlying
bedrock \citep{saintenoy2013deriving}. Additionally, all available ice
thickness measurements across the Svalbard archipelago were integrated
into a regional study to estimate total ice volume and its loss to
sea \citep{furst2018ice}. Such large-scale studies are crucial for
improving projections of future glacier mass loss and its impact on sea
levels. A fundamental challenge in glacier volume estimation is
accurately defining the glacier's contours. This issue has been
addressed by multiple research groups employing GPR to delineate
glacier extents and improve volume
calculations \citep{santin2023b,Bernard2014,bernard2024glacier}.

The geometry reconstruction of the Irenebreen glacier
(Svalbard) \citep{karuvss2022uav} highlights the importance of
multi-offset GPR measurements, as developed by \citet{booth2008}
and \citet{murray2007water}. These techniques are particularly valuable
for distinguishing between solid and liquid water within a
glacier \citep{barrett2007errors} and for constraining its thermal
state \citep[see also the thermal state assessments
by][]{woodward2003glacier,schannwell2014automatic}.
The challenge of differentiating liquid and solid ice has been
extensively studied, notably on the T\^ete Rousse glacier (France).
There, GPR, combined with Nuclear Magnetic Resonance (NMR) data, was
employed to characterize and monitor an internal water-filled cavity.
This monitoring was crucial in guiding the controlled drainage of water
to mitigate the risk of catastrophic flooding in the downstream
valley \citep{garambois2016}.\looseness=1

In a more invasive approach, borehole GPR has been used in conjunction
with surface measurements to precisely characterize englacial water
distribution, as demonstrated by \citet{murray2000englacial}.
Additionally, variations in radar amplitude have been exploited to
infer water content within the basal substrate beneath the Rutford Ice
Stream in Antarctica \citep{schlegel2022radar}. These variations in
basal layer properties play a crucial role in ice flow modeling,
further emphasizing the importance of geophysical techniques in
glaciological research.\looseness=-1

Moraine areas are more challenging for GPR survey as they are composed
by rocks from several sizes, sediments and/or large blocks, inducing
dispersion and multiple diffraction
phenomena \citep{lonne1996architecture}. These observed diffractions
can actually help to understand the process of glacial thrusting or
proglacial shear, as done for the first time
by \citetalias{lonne1996architecture} to relatively date the occurrence of
the glacial deformation and where it was mainly applied.  The ability
to discriminate between sediment and ice within glacial environments
was further demonstrated by \citet{murray2010}, who reconstructed 3D
englacial sediment structures at the front of the surging Kongsvegen
Glacier (Svalbard). Similarly, \citet{midgley2013} used multiple
100-MHz GPR profiles to infer the internal structure of the moraine in
front of the Austre Lovenbreen Glacier (Svalbard). Through
common-midpoint velocity analysis, they identified differences in
subsurface composition, revealing that the outer moraine contains a
significant volume of buried ice, whereas the frontal zone moraine is
more sediment-rich. These variations were linked to past glacier
surging activity, as evidenced by a surface bulge. Their findings
highlight the role of moraine structures as archives of
paleoglaciological information from the Neoglacial period.

Rock glaciers have gained significant attention as key indicators for
assessing the impacts of climate change on mountain permafrost. Under
specific topographic conditions, their destabilization can lead to
surface velocities of up to 10 m per year \citep{marcer2021}. GPR has
proven to be an effective tool for investigating rock glaciers. For
instance, \citet{buchelt2024} conducted a study on the Tellers Davains
rock glacier in the central Swiss Alps using a PulseEkko 50~MHz system,
achieving a penetration depth of approximately 15 m in the most
resistive sections along a 1-km-long profile. A broader comparative
study by \citet{meng2023} examined four rock glaciers across Alaska,
Wyoming, and Colorado. Using a 25~MHz antenna, they achieved a
penetration depth of 50 m, enabling them to infer volumetric ice
fractions. Their analysis linked these ice fractions to past ice
accumulation and subsurface ice preservation processes. Notably, they
highlighted the relevance of their findings for planetary exploration,
particularly in the context of Mars, where numerous debris-covered
glaciers suggest subsurface ice reservoirs.\looseness=-1

Access difficulty pushed for the development of airborne GPR,
introducing a mid-scale between on-ground and satellite
measurements \citep{rutishauser2016helicopter}, with pioneering
explorations on the King George Island ice cover,
Antarctica \citep{kim2010helicopter,ruckamp2012king}.
\citet{kim2010helicopter} tested a 100 MHz GPR, antenna under an
helicopter, and \citet{ruckamp2012king} used the BGR-P30-System
developed at the University of Munster as a fast and efficient tool for
mapping heavily crevassed coastal areas. In the continuity of these
aerial data acquisition mode, some drone-based GPR are now available
for glacier studies  \citep[e.g.][]{ruols2023development}.\looseness=-1

\subsection{Snowpack analysis}

At the other end of the resolution spectrum, GPR was also applied to
snowpack studies to measure snow-depth, -density, and -layer
stratigraphy, aiming, in fine, to study seasonal snow accumulation
\citep{annan2001}, and monitoring water resources in snow-dominated
hydrological regime regions
\citep{griessinger2018,yildiz2021,mccormack2019, vergnano2022,
valence2022}. 

Similar to mountaineous permafrost, collecting data on snow
stratigraphy within potential avalanche zones, assessing stability, and
aiding in avalanche forecasting require access to snow cover in remote
and challenging mountainous terrains. This was one of the first
motivations for UAV-mounted studies \citep{mccormack2019,
vergnano2022}. 

Heterogeneity in firn (ice that is at an intermediate stage between
snow and glacial ice) can be assessed with GPR. More precisely, its
response to seasonal percolation, with validation using cores and
numerical modeling is the subject of \citet{brandt2009}. However
ground-based GPR applications necessitate direct contact with the snow
surface, which alters its properties and renders subsequent surveys
less representative of natural conditions. UAV GPR is a very promising
method for precise snow hydrology studies \citep{valence2022}.\looseness=-1

\citet{griessinger2018} use a system of four pairs of antenna in a way
that they could acquire repeated profiles in the Swiss Alps in winter
seasons. Their results open the way of new data sets acquisitions to
validate snow melt models or to complement lidar-based snow surveys.
The potential of combining Uncrewed Aerial Vehicle (UAV) photogrammetry
with GPR to map snow water equivalent at large scales is again shown in
\citet{yildiz2021}. UAV photogrammetry provides high-resolution,
spatially continuous snow depth measurements at the basin scale. GPR
complements this by enabling non-destructive snow investigations,
allowing snow density to be estimated from radar velocities derived
using photogrammetric snow depths and GPR two-way travel times at the
snow-ground interface.

The development of upward-looking GPR to study snow cover properties
has been done by \citet{heilig2009} and \citet{schmid2014}.  The
integration of Water Content Reflectometry (WCR) and upward-looking GPR
(1500~MHz) was tested in the Western Italian Alps from November to
April \citep{godio2018} and showed to provide high accuracy in
monitoring average snow density values. Furthermore, the combined use
of upward GPR, water content probes, and conventional snow depth
observations enables a detailed analysis of snow deposition, settlement
phases, densification processes, and the melting and freezing phases.

\subsection{Infrastructure characterisation and monitoring}

As cold regions through the arctic anomaly is subject to stronger
amplitude warming, the human \mbox{infrastructures} face a large panel of
disturbances, such as frost heave and thawing permafrost leading to
house instability, road damages and all the landslide and terrain
movement
consequences \citep{lamoureux2015,yu2014,tregubov2020,tregubov2024}.


GPR was used to monitor roadbed
conditions \citep{oldenborger2015,fortier2011}, airport
airfield \citep{jorgensen2007}, pipeline
stability \citep{wang2016,oswell2011}, and bridge pile
foundations \citep{you2017}. It can detect voids or changes in soil
moisture that could lead to structural failures. It is also a tool to
monitor the thermal effects on the surrounding material when trying to
insulate the pipes with thermosyphons \citep{wang2016} or evaluate
cooling measures effectiveness for highway maintenance when built over
permafrost \citep{stephani2014,huang2024}. 

\subsection{Subsurface investigations on the moon and mars}

Looking for water traces in the shallow subsurface of Mars as well as
understanding the internal structure of the Moon to get indices of its
history, have been exciting topics for many
years \citep{schroeder2020five}. At first several orbiters equipped
with radar systems have been sent around the
Moon \citep{phillips1973apollo,peeples1978orbital,ono2010lunar} and
around Mars \citep{seu2007sharad,picardi2005radar}. They were followed
by {in-situ} GPR mounted on uncrewed
rovers \citep{li2015chang,hamran2020,zou2024} to obtain higher
resolution data that can be cross-validated with data from the
orbiters. 

Chang'E-3(CE-3) was the first GPR deployed on the Moon surface onboard
a rover in December 2013 \citep{li2015chang}. A 114-m long profile was
acquired and first interpretations allowed to distinguish regoliths,
paleo-regolith and ejecta layer \citep{su2014data,fa2015regolith}.
However \citet{li2017pitfalls} alerted for signal artefacts due to the
metallic rover, that were wrongly interpreted as coming from deep
reflectors. This study illustrates the importance of testing the data
acquisition and interpretation on Earth with similar systems as those
sent to space \citep{soldovieri2009preparatory}.  {In-situ} Moon GPR
investigations went on with Chang'E-4 that landed on the other side of
the moon in 2019 \citep{jia2018scientific}.   These missions provided
high-resolution imaging of the lunar subsurface, revealing its layered
structure and key properties like regolith thickness and composition,
significantly advancing our understanding of lunar
geology \citep{lai2019comparison}. 

For Mars subsurface exploration, two orbiting GPRs revealed key
insights into Mars' subsurface before {in situ}
measurements \citep{picardi2004,mouginot2012}. The Mars Advanced Radar
for Subsurface and Ionospheric Sounding (MARSIS), part of the Mars
Express mission, operated from July 2005 with a frequency range of 
1.3--5.5~MHz \citep{picardi2004}. Its data were interpreted in terms
of maps of dielectric constant distributions, suggesting a Late
Hesperian ocean in the Utopia Planitia region \citep{mouginot2012}. 
SHAllow RADar (SHARAD), with higher resolution (higher frequency range
of 15--25~MHz), on-board the Mars Reconnaissance Orbiter, has been
working since 2006. SHARAD has revealed the internal structure,
composition, and history of Mars' polar caps, showed that mid-latitude
glacial landforms are ice-rich debris-covered glaciers, and has
provided first constraints on the interior composition and stratigraphy
of volcanic and sedimentary layers \citep{putzig2024}.

Meanwhile, Perseverance is a rover that landed on Mars in February 2021
inside the Jezero 45-km diameter crater \citep{bell2021mars}. This
rover is equipped with a monostatic frequency modulated continuous wave
radar, acronym RIMFAX,  that operates in the frequency range 150~MHz to
1.2~GHz. A detailed instrument description is in \citet{hamran2020}. An
interpretation of the first 3-km long radargram recorded with RIMFAX is
presented in \citet{hamran2022}. It reveals dipping reflectors with
cross beddings that could be explained either by magmatic or
sedimentary layering. \citet{casademont2023} present the statistical
distribution of the EM velocity  retrieved from 150 hyperbolas observed
along the radargram at different arrival times. Each velocity value is
the average from the surface down to the diffracted point creating the
studied hyperbola. It varies from 0.07 up to 0.21 m/ns. Assuming a dry,
non-magnetic and low-loss medium, the velocity is converted to relative
dielectric permittivity with values varying from 2 to 20. In
\citet{eide2023} the radar attenuation, estimated from the returned
signal power itself, is quite constant all along the studied profile.
Both quantities, dielectric permittivity and attenuation rate, can not
help to clearly identify the lithology of the different layers, which
interfaces give radar reflections.  

In May 2021, four months after Perseverance, the Tianwen-1
mission \citep{zou2021scientific} deployed successfully the Zhurong
rover to explore an area south of the Utopia Planitia with onboard the
Rover Penetrating Radar (RoPer). This device works at two different
frequency ranges, the first being with higher frequency range (450--2150
MHz) than the other one (15--95 MHz). The high frequency system is
recording full polarimetric data. It is the first tool with this
possibility to work on another planet surface (it is worth noting that
a French team \citep{ciarletti2017} has been working for years for a
full-polarimetric GPR system mounted on a rover, the Water Ice
Subsurface Deposit Observation on Mars (WISDOM)). The data were
acquired with distance steps of either 25~cm or 50~cm.  The first 1100
m of the profile acquired with the lower-frequency range has been
interpreted as multi-layered media of different granulometric sequences
analysing signal from diffractors as deep as 80 m \citep{li2022}. With
the higher frequency range system, \citet{zou2024} present a processing
strategy to estimate surface relative permittivity using HH and VV
channels, based on the induced field rotation effect, which occurs when
orthogonal EM waves propagate into an uneven surface with incident
angles. A rough surface model was produced by employing colour images
captured by the Navigation and Topography Camera (MSCam) located on the
Zhurong Rover.  As with the RIMFAX data, a velocity analysis has been
carried on several hyperbolas using the high frequency data by
\citet{liu2023}. More interpretation of the high frequency data have
been carried on by \citet{sun2025}. 

\section{Key innovations in the last 3 decades and yet to come}

Over the last thirty years, significant advancements in GPR
technologies have facilitated its application in cold regions. These
developments encompass a broad spectrum of innovations, ranging from
data acquisition techniques to open-source software and hardware. In
the following section, we will highlight several key advancements,
firstly in hardware and subsequently in software, and their
implications. More insights in the technology future can be found in
the review of \citet{schroeder2022paths}.

\subsection{Hardware evolution}

Recent progress in 3D field acquisition have been a game changer. In
the 1990s, antenna had to be linked via coaxial cables to the control
unit, which were of such substantial size that the use of a wheelbarrow
was necessary for mobility (see photographs of the GSSI SIR-10 control
unit \citep{GSSI}). The use of optical fibers and the control unit
miniaturisation marked a first improvement for impulse GPR field
acquisition.  Furthermore, recent advancements in technology enable the
stacking of thousands of signal traces, significantly enhancing data
quality by reducing noise \citep[e.g.\ the ultra receiver described
in][]{annan2018}.

Contemporary, multi-antenna systems, equipped with up to 12 pairs of
antennas, in conjunction with RTK GPS positioning, are a giant leap in
comparison with the pioneering ``wheelbarrow GPR'' systems. These
modern multi-antenna systems facilitate the coverage of extensive
surface areas, reaching up to one hectare within a span of half a day. 
At present, the primary applications of these systems are in the domain
of archaeological prospection \citep{trinks2010efficient}, in flat
terrains as the bulky nature of this equipment currently limits its
deployment in remote or topographically challenging environments.

As was outlined in the preceding sections of this document, the
investigation of permafrost and analogous frozen features has given
rise to considerable challenges with regard to accessibility. The
primary solution to the problem of inaccessibility in remote regions
has been the utilisation of
helicopters \citep{kim2010helicopter,ruckamp2012king}. This acquisition
mode is susceptible to directional artifacts arising from the
orientation of dipole antennas relative to undulating subsurface
interfaces. To address this limitation, a dual-polarization GPR system
was developed at ETH Zurich and has been successfully deployed to image
several Alpine glaciers \citep{langhammer2019glacier,grab2021ice}. 

Another way has been indicated by the Moon and Mars exploration with
the developments in uncrewed
equipments \citep{li2015chang,hamran2020,zou2024,arcone2016robot,ravnaas2023marine}. 
The scope of GPR applications has been expanded through the utilisation
of satellites and rovers, and it is anticipated that this scope will
continue to expand in the future with the augmentation of UAV payload
capacity. GPR systems mounted on uncrewed rovers have been deployed for
planetary exploration \citep{li2015chang, hamran2020, li2022} but also
for terrestrial investigations in Antarctica \citep{arcone2016robot}.
Drone-borne GPR has been explored for applications such as landmine
detection \citep{vsipovs2020UAV}, soil moisture
mapping \citep{wu2019new} and alpine glacier
surveying \citep{ruols2023development}. It was also tested for lake
bathymetry map \citep{bandini2023mapping}, which inspires the
feasibility of integrating GPR with uncrewed water surface systems for
lake or riverbed investigations such as the one used with marine
seismic equipment by \citet{ravnaas2023marine}.

Aerial imaging technologies, including high-resolution topographic
mapping and vegetation analysis such as greenness maps, support GPR
surveys by identifying optimal survey locations and providing
contextual data that helps the interpretation of GPR
results \citep{helfricht2014lidar,krutskikh2023,leger2023syrdakh}.
Furthermore, advancement in low-energy soil sensors, including those
measuring soil water content and temperature, are encouraging
{in situ} measurements used to constrain information from the
field \citep{leger2019DTP}. A particularly promising category is
embedded passive sensors activated by surface GPR signal, as described
in \citet{friedt2018acoustic}. This innovation paves the way for
long-term {in situ} sensing and monitoring of various
environmental parameters, such as gas and water
chemistry.

The advent of open-source solutions has had a democratising effect on
access to advanced GPR technologies.  Open hardware initiatives in
geophysics \citep[e.g.][]{clement2020ohmpi} have introduced innovative
and cost-effective approaches to GPR development.  For instance, a
home-made GPR built from off-the-shelf components was successfully
tested under cold chamber conditions \citep{leger2023brief}. This
device was developed for the purpose of autonomous, long-term
monitoring as a standalone automated apparatus, combining an antenna
and a vector network analyser, both of which driven by a single-board
computer with embarked filtering processes. All of this was aiming to
\mbox{enhance} thermo-hydrodynamic characterisation of the active layer in
remote regions while minimising impact on the study area.  Standalone
automatic devices are particularly relevant given the growing concerns
over travel-related carbon emissions, restrictions imposed during
global pandemics, and practical challenges such as transporting
expensive and sensitive equipment across international\break borders.

\subsection{Software evolution}

Numerical modeling tools, such as GprMax \citep{Warren2016}, have
significantly advanced the interpretation of GPR data, particularly in
the heterogeneous environments characteristic of cold regions. These
tools enable researchers, teachers and students, to simulate GPR
responses and compare them with real data, incorporating increasingly
detailed models, such as the presence of vegetation on the
surface \citep{giannakis2015realistic}. Moreover, this software allows
for the modeling of antenna behavior and the integration of a
stochastic distribution of electromagnetic properties within materials
using a fractal approach and sub griding
the mesh to model for example the antennas \citep{wei2017subgridded}.

The integration of multiple geophysical methods for characterizing
cold-region features has proven valuable in refining data
interpretation \citep{benjumea2003estimation,pavoni2023characterization,pavoni2023combining,steiner2021,garambois2016}. 
Techniques such as refraction seismic, ERT, and EM induction provide
complementary information to GPR, aiding in the estimation of ice
properties and bedrock characteristics \citep{benjumea2003estimation}.
An other example of multiple method integration is the investigation of
a small glacier in the Italian Alps with GPR and frequency-domain EM
measurements \citep{pavoni2023combining}.  Most data processing
software is specialized for a single geophysical method, making the
interpretation of multi-method datasets challenging. Effective analysis
requires software capable of integrating and processing diverse
geophysical datasets.

Over the past decade, there has been a significant rise in open-source
scientific computing tools, widely accessible through platforms such as
the Python programming language and Jupyter Notebook environments.
Notable examples include open-source GPR data processing
tools \citep{plattner2020gprpy,ralston2012software}. Collaborative
efforts to integrate GPR data with other open-source geophysical
platforms, such as PyGIMLi \citep{rucker2017pygimli}, have facilitated
multi-method interpretations and fostered interdisciplinary research,
as demonstrated in \citet{pavoni2023characterization}.\looseness=1

The geophysical community, and GPR data processing in particular, has
greatly benefited from the rapid advancements in Artificial
Intelligence (AI) \citep{yu2021deep}. Early applications focused on
automatic hyperbola detection for reflector positioning in zero-offset
profiles \citep{maas2013using}. More recently, convolutional neural
networks, combined with the You Only Look Once (YOLO) algorithm, have
been employed to automatically extract signals for utility detection in
urban environments and road prospecting \citep{liu2023automatic}. A
decade earlier, full-waveform inversion (FWI) represented a major
breakthrough in GPR processing, successfully applied to crosshole
data \citep{ernst2007application,klotzsche2019review} and surface
recordings \citep{lambot2009remote,lavoue2014two}. Recent advancements
have introduced frequency-dependent FWI techniques capable of handling
dispersive media, improving conductivity reconstruction in highly
attenuating, high-permittivity environments \citep{qin2023full}, with
successful application on multi-offset surface GPR
data \citep{qin2024application}. The integration of AI with FWI now
enables real-time GPR data interpretation, facilitating rapid
decision-making in the field. For example, \citet{xue2024real}
developed a deep learning-guided network that incorporates geological
and geophysical knowledge to translate zero-offset GPR data into
dielectric permittivity and electrical resistivity profiles in real
time. This approach was successfully applied to GPR data collected
above a pollutant spill, demonstrating its potential for environmental
monitoring and subsurface characterization.\looseness=-1

Real-time acquisition, visualization, and interpretation are
particularly advantageous for applications in cold regions, enabling
adaptive survey planning in response to field conditions. This
capability is especially valuable in remote areas, where it can enhance
operational efficiency and significantly reduce logistical costs.

\section{Conclusion}

In this brief review, we have provided a non-exhaustive overview of GPR
studies focused on characterizing cold-region features, including
permafrost and its active layer, pingos and other large ice bodies,
glaciers and their associated moraines, as well as subsurface
investigations on extraterrestrial bodies such as the Moon and Mars. We
emphasized the strong connection between technological advancements and
progress in GPR measurements and data processing, driven by hardware
miniaturization and increasingly efficient algorithms. We believe that
the seamless integration enabled by these hardware and software
breakthroughs paves the way for research teams to develop customized,
low-cost, energy-efficient, and lightweight (semi-) automated GPR
systems tailored to their specific needs.  Such devices can be deployed
in the field for long-term, continuous monitoring, facilitating the
observation of complex environmental phenomena in harsh and remote
regions. Furthermore, we foresee opportunities for participatory
science, fostering new collaborations between researchers and local
communities who are directly affected by the ongoing impacts of climate
change. This synergy can enhance data collection while empowering
communities to actively contribute to scientific research and
environmental monitoring.

\section*{Declaration of interests}
The authors do not work for, advise, own shares in, or receive funds
from any organization that could benefit from this article, and have
declared no affiliations other than their research organizations.

\section*{Dedication}

The manuscript was written through contributions of all authors. All
authors have given approval to the final version of the manuscript.

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