Brief History of Radar Meteorology

•Christian Hulsmeyer developed a device that could detect the presence of ships (1904)•Tesla (1917) outlined a Radar could be used for vessel tracking•Pulsing (ranging) radar first developed during 1930s by British, German, French, and US researchers for defense•German developments were thought by the Allies to be focused on “death rays”•20 Feb 1941 10-cm (S-band) radar used to track rain showers (Ligda)•Possibility of such observations was predicted by Ryde (1941)•MIT Radiation Laboratory made similar observations in the early 1940s•U.S. Air Corps meteorologists receive “radar” training at MIT in 1943•First operational weather radar, Panama, 1943•Science of radar meteorology born from WWII research

Radar Image from 15 July 1960Hurricane Abby near BelizeU.S. Navy photograph

RADAR-Radio Detection and Ranging

Radar is the “art of detecting by means of radio echoes the presence of objects, determining their direction and range, recognizing their characteristics and employing the data thus obtained”.

“Object” refers to meteorological targets such as raindrops, hailstones, cloud ice and liquid particles and snowflakes. For the purpose of clear air detection, insects are considered the “objects”. Birds also are readily detected and hence are of interest.

Radar is based on the propagation of electromagnetic waves through the atmosphere, a non-vacuum. EM waves propagate at the speed of light in a vacuum, c = 2.998 x 108 m s-1.

Propagation speed in a non-vacuum determines the index of refraction, n = c/νwhere ν is the wave speed

Some of the Uses of Radar in Meteorology

•Precipitation measurements•Wind measurements•Turbulence and wind shear detection•Nowcasting•Hail and aircraft icing detection•Location of melting level in stratiform precipitation•Mesocyclone and TVS detection•Wind soundings in stratiform precipitation•Hurricane structure•Wind data assimilation in numerical weather prediction models•Extrapolation forecasting of severe weather

W and K band radars are “cloud radars”X, C, S and L band radars are “precipitation radars”

Also - Wind Profilers (UHF & VHF; ~50 to 900 MHz; ~6 to 0.3 m)

Examples of Radar SystemsExamples of Radar Systems

SMART RadarC-band5 cmDoppler

NWS NEXRADS-band2.85 GHz (10.5 cm)Doppler

TRMM Precipitation Radar (Ku; 13.8 GHz; 2.2 cm)

915 MHz Wind ProfilerSouthern Great PlainsARM-CART site

482 MHz German Meteorological Service Wind Profiler

Block Diagram of a Radar System

Transmitter106 W

Antenna

Receiver10-14 W

Display

T/R switch