S-band Dual Polarization, Dual Wavelength Doppler Radar

NCAR/EOL's S-PolKa radar is an advanced, transportable, ground-based dual-polarized, dual-wavelength, Doppler weather radar. S-PolKa transmits 10 cm wavelength (S-band) and 0.86 cm wavelength (Ka-band) simultaneously with matched beamwidths and range resolution. The dual-polarimetric capabilities of S-PolKa lead to improved precipitation estimates over what is available on conventional radars, as well as real-time identification of hydrometeor types. The absolute phase measurements from S-PolKa can be used to compute and monitor in real time the low-level humidity by measuring changes in refractive index between fixed ground targets. The added capabilities afforded by the dual-wavelength radar measurements currently include boundary layer humidity profiles and cloud liquid water content estimates that are independent of drop size distribution.

The derived products available on S-PolKa are summarized in the table below (click on the product name to view examples).


Derived Product  Real-time Comments References
Hydrometeor ID Yes NCAR Fuzzy logic algorithm Vivekanandan et al (1999)
Rainfall accumulation Yes Including R-Z, R-Z/ZDR, R-KDP and a hybrid  
Near surface humidity Yes From refractive index estimates Weckwerth et al. (2005), Fabry (2004), Fabry et al. (1997)
Boundary layer humidity Yes Dual-wavelength method Ellis and Vivekanandan (2010)
Cloud Liquid water content No Dual-wavelength method Ellis and Vivekanandan (2011)


The S-PolKa transmitter can be switched instantly between fast alternating of horizontal and vertical polarizations and simultaneous transmit mode. Also, time series In-phase and Quadrature (I and Q) data can be recorded for signal processing research, algorithm development and verification.

Please note that the status of the Ka-band component of S-PolKa is currently under review and the Ka-band is not available for deployment at this stage.

Test Bed for Research and Operations

S-PolKa 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). The work includes mitigation of range/velocity ambiguities and ground clutter contamination, calibration of differential reflectivity (ZDR) and development and verification of dual-polarimetric rain rate algorithms to compare with the NEXRAD polarization retrievals. The real-time Clutter Mitigation Decision (CMD) algorithm identifies and removes clutter before the final moments are computed and does not apply a clutter filter to regions without contamination. The result is much cleaner data without clutter filter bias of the weather echoes. The CMD algorithm can operate on current NEXRAD data or utilize dual-polarimetric data and is available on S-PolKa. The so-called S-Z phase coding algorithms can recover (rather than censor) overlaid echoes, effectively doubling the unambiguous range. This allows use of shorter pulse repetition times (PRT) and larger Nyquist velocity values. Click here for more information on EOL's NEXRAD data quality program.


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