Radioglaciology is the study of

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at La ...

s, ice caps and

icy moon Icy commonly refers to conditions involving ice, a frozen state, usually referring to frozen water. Icy or Icey may also refer to: People * Icy Spicy Leoncie, an Icelandic-Indian musician Arts, entertainment, and media Music * ICY (band), a voca ...

s using ice penetrating radar. It employs a

geophysical Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' some ...

method similar to

ground-penetrating radar Ground-penetrating radar (GPR) is a Geophysics, geophysical method that uses radar pulses to Geophysical imaging, image the subsurface. It is a non-intrusive method of surveying the sub-surface to investigate underground utilities such as concrete, ...

and typically operates at frequencies in the MF, HF, VHF and UHF portions of the

radio spectrum The radio spectrum is the part of the electromagnetic spectrum with frequencies from 0 Hz to 3,000 GHz (3 THz). Electromagnetic waves in this frequency range, called radio waves, are widely used in modern technology, particula ...

. This technique is also commonly referred to as "Ice Penetrating Radar (IPR)" or "Radio Echo Sounding (RES)". Glaciers are particularly well suited to investigation by radar because the

conductivity Conductivity may refer to: *Electrical conductivity, a measure of a material's ability to conduct an electric current **Conductivity (electrolytic), the electrical conductivity of an electrolyte in solution ** Ionic conductivity (solid state), ele ...

, imaginary part of the

permittivity In electromagnetism, the absolute permittivity, often simply called permittivity and denoted by the Greek letter ''ε'' (epsilon), is a measure of the electric polarizability of a dielectric. A material with high permittivity polarizes more in ...

, and the

dielectric absorption Dielectric absorption is the name given to the effect by which a capacitor, that has been charged for a long time, discharges only incompletely when briefly discharged. Although an ideal capacitor would remain at zero volts after being discharged, ...

of ice are small at

radio frequencies Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around . This is roughly between the upper ...

resulting in low loss

tangent In geometry, the tangent line (or simply tangent) to a plane curve at a given point is the straight line that "just touches" the curve at that point. Leibniz defined it as the line through a pair of infinitely close points on the curve. Mo ...

skin depth Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the surface of the conductor and decreases exponentially with greater depths in the co ...

, and attenuation values. This allows echoes from the base of the ice sheet to be detected through ice thicknesses greater than 4 km. The subsurface observation of ice masses using radio waves has been an integral and evolving

technique in

glaciology Glaciology (; ) is the scientific study of glaciers, or more generally ice and natural phenomena that involve ice. Glaciology is an interdisciplinary Earth science that integrates geophysics, geology, physical geography, geomorphology, c ...

for over half a century. Its most widespread uses have been the measurement of ice thickness, subglacial topography, and ice sheet stratigraphy. It has also been used to observe the subglacial and conditions of ice sheets and glaciers, including hydrology, thermal state, accumulation, flow history, ice fabric, and bed geology. In planetary science, ice penetrating radar has also been used to explore the subsurface of the Polar Ice Caps on Mars and comets. Missions are planned to explore the icy moons of Jupiter.

Measurements and applications

Radioglaciology uses

nadir The nadir (, ; ar, نظير, naẓīr, counterpart) is the direction pointing directly ''below'' a particular location; that is, it is one of two vertical directions at a specified location, orthogonal to a horizontal flat surface. The direc ...

facing

radar Radar is a detection system that uses radio waves to determine the distance ('' ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, we ...

s to probe the subsurface of

s, ice caps, and

s and to detect reflected and scattered energy from within and beneath the ice. This geometry tends to emphasize

coherent Coherence, coherency, or coherent may refer to the following: Physics * Coherence (physics), an ideal property of waves that enables stationary (i.e. temporally and spatially constant) interference * Coherence (units of measurement), a deri ...

and

specular Specular reflection, or regular reflection, is the mirror-like reflection of waves, such as light, from a surface. The law of reflection states that a reflected ray of light emerges from the reflecting surface at the same angle to the surfac ...

reflected energy resulting in distinct forms of the radar equation. Collected radar data typically undergoes

signal processing Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing ''signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...

ranging from stacking (or pre-summing) to

migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...

to Synthetic Aperture Radar (SAR) focusing in 1, 2, or 3 dimensions. This data is collected using ice penetrating radar systems which range from commercial (or bespoke) ground penetrating radar (GPR) systems to coherent, chirped airborne sounders to swath-imaging, multi-frequency, or

polarimetric Polarimetry is the measurement and interpretation of the polarization of transverse waves, most notably electromagnetic waves, such as radio or light waves. Typically polarimetry is done on electromagnetic waves that have traveled through or ...

implementations of such systems. Additionally, stationary, phase-sensitive, and Frequency Modulated Continuous Wave (FMCW) radars have been used to observe snow, ice shelf melt rates, englacial hydrology, ice sheet structure, and vertical ice flow.

Interferometric Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

analysis of airborne systems have also been demonstrated to measure vertical ice flow. Additionally, radioglaciological instruments have been developed to operate on autonomous platforms, on in-situ probes, in low-cost deployments, using Software Defined Radios, and exploiting ambient radio signals for passive sounding. The most common scientific application for radioglaciological observations is measuring ice thickness and bed topography. This includes

interpolated In the mathematical field of numerical analysis, interpolation is a type of estimation, a method of constructing (finding) new data points based on the range of a discrete set of known data points. In engineering and science, one often has a n ...

"bed maps", widely used in ice sheet modeling and sea level rise projections, studies exploring specific ice-sheet regions, and observations of glacier beds. The strength and character of radar echoes from the bed of the ice sheet are also used to investigate the

reflectivity The reflectance of the surface of a material is its effectiveness in Reflection (physics), reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the respon ...

of the bed, the

attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variabl ...

of radar in the ice, and the

morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts * Morphology (astronomy), study of the shape of astronomical objects such as nebulae, galaxies ...

of the bed. In addition bed echoes, radar returns from englacial layers are used in studies of the radio stratigraphy of ice sheets including investigations of ice accumulation, flow, and

fabric Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, different fabric types, etc. At first, the word "textiles" only referred to woven fabrics. However, weaving is not th ...

as well as absence or disturbances of that stratigraphy. Radioglaciology data has also been used extensively to study

subglacial lake A subglacial lake is a lake that is found under a glacier, typically beneath an ice cap or ice sheet. Subglacial lakes form at the boundary between ice and the underlying bedrock, where gravitational pressure decreases the pressure melting point ...

s and glacial

hydrology Hydrology () is the scientific study of the movement, distribution, and management of water on Earth and other planets, including the water cycle, water resources, and environmental watershed sustainability. A practitioner of hydrology is call ...

including englacial water, firn aquifers, and their temporal evolution. Ice penetrating radar data has also been used to investigate the subsurface of

ice shelves An ice shelf is a large floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface. Ice shelves are only found in Antarctica, Greenland, Northern Canada, and the Russian Arctic. The b ...

including their grounding zones, melt rates, brine distribution, and basal channels.

Planetary exploration

There are currently two ice-penetrating radars orbiting

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

MARSIS MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) is a low frequency, pulse-limited radar sounder and altimeter developed by the University of Rome La Sapienza and Alenia Spazio (today Thales Alenia Space Italy). The Italian MAR ...

and

SHARAD Sharad/Sarath/Sharath ( sa, शरद्)is the autumn season or ritu in the Hindu calendar. It roughly corresponds to the western months of mid-September to mid-November. Sharad is preceded by Varsha and followed by Hemant. The Hindu calendar c ...

. An ice penetrating radar was also part of the ROSETTA mission to

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

67P/Churyumov–Gerasimenko 67P/Churyumov–Gerasimenko (abbreviated as 67P or 67P/C–G) is a Jupiter-family comet, originally from the Kuiper belt, with a current orbital period of 6.45 years, a rotation period of approximately 12.4 hours and a maximum velocity of . Chu ...

. Ice penetrating radars are also included in the payloads of two planned missions to the

s of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

JUICE Juice is a drink made from the extraction or pressing of the natural liquid contained in fruit and vegetables. It can also refer to liquids that are flavored with concentrate or other biological food sources, such as meat or seafood, such as ...

and

Europa Clipper Europa Clipper (previously known as Europa Multiple Flyby Mission) is an interplanetary mission in development by NASA comprising an orbiter. Planned for launch in October 2024, the spacecraft is being developed to study the Galilean moon Eur ...

IGS symposia

The International Glaciological Society (IGS) holds a periodic series of symposia focused on radioglaciology. In 2008, the "Symposium on Radioglaciology and its Applications" was hosted at the

Technical University of Madrid The Technical University of Madrid or sometimes called Polytechnic University of Madrid ( es, Universidad Politécnica de Madrid, UPM) is a public university, located in Madrid, Spain. It was founded in 1971 as the result of merging different Te ...

. In 2013, the "Symposium on Radioglaciology" was hosted at the

University of Kansas The University of Kansas (KU) is a public research university with its main campus in Lawrence, Kansas, United States, and several satellite campuses, research and educational centers, medical centers, and classes across the state of Kansas. T ...

. In 2019, the "Symposium of Five Decades of Radioglaciolgy" was hosted at Stanford University.

Research institutions

Research and education in radioglaciology is undertaken at universities and research institutes around the world. These groups found in institutions and departments that span

physical geography Physical geography (also known as physiography) is one of the three main branches of geography. Physical geography is the branch of natural science which deals with the processes and patterns in the natural environment such as the atmosphere, ...

geophysics Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' so ...

, earth science, planetary science, electrical engineering, and related disciplines.

References

{{reflist Glaciology

Measurements and applications

Planetary exploration

IGS symposia

Further reading

Research institutions

References