The S-band Dual Polarization Doppler Radar (S-Pol) is a research-grade, transportable, ground-based, dual-polarized, Doppler weather radar. As an S-band radar, S-Pol is sensitive to a wide range of echo types and particle sizes from clear air (primarily via insects) and cloud echoes to severe storms containing heavy precipitation and hail. S-Pol observations provide high-resolution information about precipitation rates, microphysics, and storm structures and kinematics. The radar has been used for many types of research, including weather and climate prediction, monsoon rainfall, and convection initiation.

S-Pol in Boulder.

An innovative system design eliminates the need for a radome and allows for S-Pol to be packed into eight standard 20 ft shipping containers that provide a base when the radar is set up. The radar needs only minimal surface site preparation and its relative ease of transport makes S-Pol a valuable tool for studying precipitation and cloud processes at remote sites around the world.

S-Pol is also used as a test bed for development of algorithms to improve the data quality of the National Weather Service's operational weather radar network (NEXRAD). Read more about EOL's NEXRAD data quality program.


The S-Pol transmitter can be switched instantly between fast alternating of horizontal and vertical polarizations and simultaneous transmit mode. S-Pol’s Range Height Indicator (RHI) mode provides detail of the vertical structure of a storm. Advanced signal processing software, along with the option to scan more slowly than surveillance radars, produces research-quality data.

Parameter Specification
Transmitter 2.7-2.9 GHz
Transmit wavelength 10 cm
Pulse width 1.0 to 1.5 µsec-tapered
Pulse repetition frequency (PRF) 1000 Hz (range = 500 to 1300Hz)
Peak power >600 kW
Noise power -114 dBm
Radar Noise figure 3 dB
Dynamic range 90 dB
Bandwidth 1 MHz, typical
Minimum detectable dBZ at 50km/1km -10.4 dBZ/-44.4 dBZ
Polarization switching H-V alternating, H-V simultaneous or H or V only
Mechanical switch isolation 47 dB measured
Antenna parabolic, center feed
Gain 44.5 dB including waveguide loss
Diameter 8.5 m (28 ft.)
Beamwidth 0.92 degrees
First sidelobe better than -28 dB
Isolation (ICPR) better than -31 dB
Scan rate Up to 12°/s for PPIs; 6 deg/s for RHIs
Wind limit 30 m/s, operation; 54 m/s, survivability
Range resolution 150 m (range = 150 to 675 m)
Gate spacing 37.5 - 150m
Number of samples 64-1024
Times series (I/Q) capability yes
Unambiguous velocity 25 m/s


For two field projects - RICO (2004) and DYNAMO (2011) - S-Pol included a Ka-band radar with a 0.86 cm wavelength and matched beams. The Ka-band was retired in 2021 and is no longer available for deployment.


NCAR/EOL S-Pol Team. (1996). S-band Dual Polarization Doppler Radar (S-Pol). UCAR/NCAR - Earth Observing Laboratory. https://doi.org/10.5065/D6RV0KR8.