What Is Meteorological Radar?

Meteorological radar is a remote sensing technology that uses microwave or radio-frequency energy to detect, measure, and track atmospheric precipitation and wind fields. By transmitting pulses of electromagnetic energy and measuring the backscatter returned by hydrometeors (rain drops, ice crystals, snowflakes, and hail), a meteorological radar determines the location, intensity, and in Doppler-capable systems, the radial velocity of precipitation. The technique provides spatial coverage over hundreds of kilometers at temporal resolutions of minutes, making it the primary observational tool for operational weather forecasting, severe storm warning, and quantitative precipitation estimation.

The physics of meteorological radar rest on Rayleigh scattering at microwave wavelengths commonly used for weather observation (S-band at approximately 10 cm, C-band at 5 cm, and X-band at 3 cm), where the returned power is proportional to the sixth power of the particle diameter, a quantity encapsulated in the radar reflectivity factor Z. Conversion between Z and rainfall rate R (the Z-R relationship) is a central calibration problem in operational meteorology, complicated by the variability of drop size distributions across storm types and geographic regions.

Doppler Radar and Wind Profiling

Doppler meteorological radars measure the phase shift between successive transmitted pulses to compute the radial velocity of scatterers moving toward or away from the antenna. This radial velocity field reveals internal storm dynamics, including the mesocyclonic rotation associated with supercell thunderstorms, convergence zones that precede convective initiation, and the shear signatures used in tornado detection. NOAA's Doppler radar explainer describes how the WSR-88D (NEXRAD) network, the operational radar backbone for the United States since the early 1990s, combines reflectivity and velocity products to produce the storm warnings issued by local Weather Forecast Offices. The NEXRAD network consists of approximately 160 S-band radars providing overlapping coverage across the conterminous United States, Alaska, Hawaii, and overseas territories.

Dual-Polarization Techniques

Conventional single-polarization radars transmit horizontally polarized pulses, which limits information to reflectivity and radial velocity. Dual-polarization radars transmit both horizontal and vertical pulses simultaneously and measure the differential reflectivity (Z_DR), the copolar correlation coefficient (CC), and the specific differential phase (K_DP) between the two channels. These additional moments enable discrimination among precipitation types (rain, wet snow, dry snow, hail), improved quantitative precipitation estimates, detection of non-meteorological scatterers such as insects and chaff, and identification of tornado debris signatures. The National Severe Storms Laboratory developed dual-polarization technology over roughly three decades before it was integrated into the U.S. NEXRAD network between 2011 and 2013, as described in NOAA's dual-polarization radar research tools. The theoretical and engineering basis for polarimetric weather radar is reviewed in IEEE publications on polarimetric weather radar principles and applications.

Radar Imaging and Backscatter Processing

Beyond Doppler wind and polarimetric precipitation products, meteorological radars are used as imaging instruments that produce plan position indicator (PPI) displays, range-height indicator (RHI) cross sections, and three-dimensional volumetric mosaics. Range folding, ground clutter suppression, beam blockage correction, and attenuation correction are standard signal processing steps applied before the meteorological retrievals. Research radars operating at X-band and Ka-band wavelengths, and cloud radars at W-band (3 mm), probe cirrus and mixed-phase cloud microphysics at spatial resolutions finer than those achievable with operational networks. Phased-array weather radars, under development as a potential successor to NEXRAD, offer rapid volumetric updates on the order of one minute by eliminating the mechanical rotation of the antenna.

Applications

Meteorological radar has applications in a range of fields, including:

• Operational weather forecasting and severe storm warning, providing near-real-time precipitation and wind data for forecast offices
• Aviation safety, detecting wind shear, turbulence, and convective hazards near airports
• Flood and flash-flood hydrology, supplying quantitative precipitation estimates for river forecasting systems
• Military and defense meteorology, monitoring atmospheric conditions relevant to weapon system performance and mission planning
• Research meteorology, characterizing cloud microphysics, storm dynamics, and precipitation processes