Earth systems and geophysics

InSAR

InSAR, or Interferometric Synthetic Aperture Radar, is a radar remote-sensing technique combining SAR images of the same area to measure millimeter-to-centimeter ground surface deformation and derive topography.

InSAR time series analysis

InSAR time series analysis is a geodetic method that measures millimeter-scale ground displacement over time from stacks of radar images, monitoring volcanoes, subsidence, and tectonic deformation.

Integer ambiguity resolution

Integer ambiguity resolution (IAR) is the estimation of unknown carrier-phase cycle-count ambiguities as integers, enabling precise GNSS positioning; methods include rounding, bootstrapping, and the LAMBDA method introduced in 1993.

Interferometric synthetic-aperture radar

Interferometric synthetic-aperture radar (InSAR) is a remote-sensing method comparing radar images from repeated satellite passes to map millimeter-scale ground deformation from earthquakes, volcanoes, and subsidence.

Oct 22, 2026

Internal structure of Mars

The internal structure of Mars is its layered crust, mantle, and core, revealed by NASA's InSight lander, which measured a thin mantle and a large, liquid iron–nickel core.

International Federation of Digital Seismograph Networks

The International Federation of Digital Seismograph Networks (FDSN) is a global organization of seismograph network operators, founded in 1984, that coordinates station siting and open data exchange.

International Geomagnetic Reference Field

The International Geomagnetic Reference Field (IGRF) is a standard mathematical model of Earth's main magnetic field, produced by IAGA and updated every 5 years since 1968.

International GNSS Service

The International GNSS Service (IGS) is a voluntary federation that collects satellite navigation data from a global network of over 400 ground stations and publishes high-precision products such as orbits and clocks.

Interrill erosion

Interrill erosion, also called sheet erosion, is the removal of soil in thin layers by raindrop impact and shallow overland flow, the first stage of water erosion on a hillslope.

Oct 22, 2026

Iron hydride

Iron hydride (FeHₓ) is a compound of iron and hydrogen, stable as a solid or melt only under gigapascal pressures and studied as a candidate component of Earth's core.

Large low-shear-velocity provinces

Large low-shear-velocity provinces (LLSVPs) are two continent-sized regions of slow seismic waves at the base of Earth's mantle, one beneath Africa and one beneath the Pacific, identified by seismic tomography.

Laser altimetry

Laser altimetry is a remote sensing method that measures surface elevation from the flight time of laser pulses, used in studies of ice, land, vegetation, and water.

Laser ranging

Laser ranging measures distances by firing short laser pulses at retroreflector-equipped satellites, the Moon, or spacecraft and timing the reflected light, underpinning Earth's reference frame and tests of general relativity.

Late veneer

The late veneer is chondritic meteoritic material that geochemical models add to Earth's mantle after core formation, explaining why highly siderophile elements like platinum remain abundant there.

Latitude

Latitude is the geographic coordinate specifying a point's north–south position on Earth as an angle from 0° at the Equator to 90° at the poles, running east–west as parallels.

Least-squares migration

Least-squares migration (LSM) is a seismic imaging method that iteratively inverts a forward modeling operator to produce images with fewer artifacts, truer amplitudes, and higher resolution than conventional migration.

Length of day variations

Length of day variations are millisecond changes in the Earth's actual rotation relative to the standard 86,400-second day, driven by tides, atmospheric winds, the liquid core, and climate change.

Lessivage

Lessivage, also called argilluviation, is the transfer of fine clay particles, chiefly under 2 μm, from a soil's eluviated E-horizon to a deeper B-horizon, producing the clay-enriched horizons of Luvisols.

List of highest points of South American countries

The highest points of South American countries are each nation's greatest elevations, from Aconcagua in Argentina at 6,960.8 m down to Uruguay's Cerro Catedral at about 514 m.

List of natural disasters by death toll

A list of natural disasters by death toll ranks events like earthquakes and floods by deaths; the deadliest listed is the 1556 Shaanxi earthquake, with about 830,000 deaths.

List of natural disasters in the United States

The list of natural disasters in the United States covers hurricanes, floods, wildfires, and earthquakes, including the deadliest events like the 1900 Galveston hurricane and Hurricane Katrina.

Lithosphere–asthenosphere boundary

The lithosphere–asthenosphere boundary (LAB) is the boundary in the uppermost mantle between the rigid lithosphere forming the tectonic plates and the ductile asthenosphere on which the plates move.

Longitude

Longitude is the geographic coordinate measuring distance east or west of the prime meridian at Greenwich, expressed in degrees and counted up to 180 in each direction.

Lunar laser ranging

Lunar laser ranging (LLR) is a geodetic technique that times laser pulses fired at retroreflector arrays on the Moon, measuring the Earth-Moon distance to millimeter precision since 1969.

Luvisols

Luvisols are a Reference Soil Group of the World Reference Base, in which clay has washed down to a base-rich subsurface horizon; they correspond to Alfisols in USDA Soil Taxonomy.

Machine learning earthquake detection

Machine learning earthquake detection uses trained neural networks to find earthquake signals in seismic recordings and pick P and S wave arrival times, replacing manual analysis.

Magnetic anomaly detection

Magnetic anomaly detection (MAD) analyzes measured local magnetic fields to detect weak magnetic sources such as buried ferromagnetic material, applied in mineral exploration, unexploded ordnance clearance, archaeology, and military submarine detection.