Weather radars rely on the presence of radiowave scattering entities such as hydrometeors and insects to sense the dynamic evolution of the atmosphere. Under clear-air, low-reflectivity conditions, when no such "visible" tracers are present, air mass boundaries such as the outflow edge of a dry microburst may go undetected. Recently, a radar data processing technique was developed to estimate the near-ground atmospheric refractivity field using ground targets. Refractivity is dependent on the moist thermodynamic variables of the atmosphere and, thus, can be used to detect air mass changes and boundaries. In this study, we apply this technique for the first time to Airport Surveillance Radar-9 (ASR-9) Weather Systems Processor (WSP) data. Comparisons with measurements from a meteorological station show good consistency. The potential exists for improving the capability of the WSP to detect low-reflectivity wind-shear phenomena by adding interest information provided by the estimated refractivity field. Adequate computational power is the sole requirement for implementing this scheme; aside from that, no alteration or addition is necessary to the ASR-9 hardware. Its primary weakness is the sensitivity to vertical variation in refractivity and variance of target height. It also has a limited range of coverage (~20 km), but that is acceptable for terminal-area coverage. Further testing is needed during more appropriate meteorological conditions and at other sites to prove that dry wind-shear events can really be detected in the derived refractivity field by this class of radar, and that the technique is robust under various topographical settings.