S-Pol

NCAR/EOL’s S-Pol radar is an advanced, transportable, ground-based dual-polarimetric 10 cm wavelength (S-band) weather radar. The dual-polarimetric capabilities of S-Pol 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-Pol can be used to compute and monitor in real time the low-level humidity by measuring changes in refractive index between fixed ground targets. S-Pol has recently been upgraded to provide simultaneous dual-wavelength radar measurements with the addition of the 0.8 cm wavelength (K_a-band) dual-polarimetric cloud radar. The added capabilities afforded by the dual-wavelength radar 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-Pol are summarized in the table below (click on the product name to view examples).

Recent hardware upgrades now enable researchers to instantly switch the S-Pol transmitter between fast alternating of horizontal and vertical polarizations and simultaneous transmit mode. Also, previously unavailable time series In-phase and Quadrature (I and Q) data can now be recorded for signal processing research, algorithm development and verification etc.

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). The work includes mitigation of range/velocity ambiguities and ground clutter contamination, calibration of differential reflectivity (Z_DR) and development and verification of dual-polarimetric rain rate algorithms in advance of the NEXRAD upgrade. 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-Pol. 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.

An innovative system design eliminates the need for a radome and allows for S-Pol to be packed into six 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-Pol a valuable tool for studying precipitation and cloud processes at remote sites around the world. The map below illustrates the S-Pol deployments through the summer of 2008, click on the map to see the full sized image.