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Radar altimetry
Radar altimetry is a satellite remote sensing technique that times microwave pulses to measure sea surface, ice, and land heights, underpinning sea level monitoring and oceanography.
Radar chart
A radar chart, also known as a spider chart or star plot, displays multivariate data on axes radiating from a common origin, joined into a closed polygon.
Radar interferometry
Radar interferometry (InSAR) is a remote sensing technique that combines radar signals from two antennas, or one antenna on repeated passes, to measure terrain elevation and surface deformation.
Radar meteorology
Radar meteorology is the branch of meteorology that uses radars for weather observations and forecasts; modern Doppler radars also measure wind motion within storms, aiding severe weather warnings.
Radar reflectivity factor
The radar reflectivity factor (Z) measures the power a weather radar receives back from raindrops, snowflakes, and ice particles, usually shown on the logarithmic dBZ scale.
Radcliffe Wave
The Radcliffe Wave is a sinusoidal chain of dense gas clouds and star-forming regions in the Milky Way, about 9,000 light-years long, discovered in 2020 through 3D dust mapping.
Radhanath Sikdar (রাধানাথ শিকদার)
Radhanath Sikdar (রাধানাথ শিকদার) was a Bengali mathematician and surveyor who, as Chief Computer of the Great Trigonometrical Survey, calculated in 1852 that Peak XV, later Mount Everest, was the world's highest mountain.
Radial acceleration relation
The radial acceleration relation (RAR) is an empirical correlation in galaxies between observed gravitational acceleration and that predicted from visible matter, established by McGaugh, Lelli, and Schombert in 2016.
Radial basis function
A radial basis function (RBF) is a function whose value depends only on the distance from a center point, a primary tool for multivariate interpolation of scattered data and for meshless solving of partial differential equations.
Radial distribution function
The radial distribution function g(r), also called the pair distribution function, describes how particle density in a liquid varies with distance from a reference particle.
Radial velocity
Radial velocity, also called line-of-sight velocity, is the component of an object's motion along the observer's line of sight, measured in astronomy from the Doppler shift of spectral lines.
Radial velocity method
The radial velocity method detects exoplanets by measuring periodic Doppler shifts in a star's spectral lines as the star moves under an orbiting planet's gravity.
Radian
The radian (rad) is the SI unit of plane angle, defined as the angle subtended by an arc whose length equals the radius; one radian is about 57.3 degrees.
Radian and steradian
The radian (rad) and steradian (sr) are the SI units of plane angle and solid angle, coherent derived units equal to one, reclassified from supplementary units in 1995.
Radian per second
The radian per second (symbol rad/s) is the coherent SI unit of angular velocity and angular frequency, differing from the hertz by a factor of 2π.
Radiance
Radiance is the radiometric measure of light power per unit projected area per unit solid angle in a given direction, measured in watts per square meter per steradian.
Radiant (meteor shower)
The radiant of a meteor shower is the point in the sky the meteors appear to come from, a perspective effect on nearly parallel paths.
Radiant energy
Radiant energy, also known as electromagnetic energy, is energy emitted, transferred, or received as electromagnetic waves, measured in joules and underlying solar irradiance, laser output, and Earth's radiation budget.
Radiation
Radiation is energy emitted from a source that travels through material or space. It takes electromagnetic forms, such as light and X-rays, and particulate forms.
Radiation burn
Radiation burn, or radiodermatitis, is tissue damage from ionizing or UV radiation that resembles sunburn but follows a delayed, cyclic schedule distinct from thermal burns.
Radiation damage
Radiation damage: injury to living tissue from ionizing radiation, via direct DNA bond breakage and indirect water-derived ions. Covers deterministic thresholds (ARS about 1 Sv), LNT stochastic cancer risk, DDREF, and radiotherapy injury such as radiation necrosis.
Radiation Effects
Radiation effects are biological changes from radiation exposure, classified as deterministic tissue reactions with dose thresholds and stochastic effects such as cancer; includes LNT model, Gy/Sv quantities, and history from Röntgen and the Curies onward.
Radiation effects on optical fibers
Radiation effects on optical fibers are the changes caused in a fiber by ionizing radiation, chiefly radiation-induced attenuation from color centers that absorb light in the glass.
Radiation Effects Research Foundation
The Radiation Effects Research Foundation (RERF) is a Japanese-American research institute studying the long-term health effects of radiation exposure in Hiroshima and Nagasaki atomic bomb survivors and their children.
Radiation exposure
Radiation exposure, also called radioactive exposure, is subjection to ionizing radiation from external sources such as X-ray machines or internal radioactive material, with health effects depending on dose.
Radiation hydrodynamics
Radiation hydrodynamics (RHD) treats radiation energy and momentum explicitly alongside the fluid, requiring simultaneous solution of fluid and radiation transport equations, and underlies models of stars, supernovae, and inertial confinement fusion.
Radiation Laboratory
The Radiation Laboratory, known as the Rad Lab, was a microwave radar research laboratory at MIT, established in 1940 to develop radar for the Allies.
Radiation pressure
Radiation pressure, also called light pressure, is the mechanical pressure exerted on a surface by electromagnetic radiation, since light carries momentum as well as energy.
Radiation pressure acceleration
Radiation pressure acceleration (RPA) is a laser-driven ion acceleration mechanism in which the momentum of an ultra-intense laser pulse pushes ions directly, as a quasi-neutral slab.
Radiation protection
Radiation protection, also known as radiological protection, is the science and practice of protecting people and the environment from ionizing radiation, organized around justification, optimization, and dose limitation.