Modeling of Zdr Bias Due to Antenna Temperature

It is well known that temperature affects the gain of electronic devices such amplifiers, circulators and modulators. It has recently been show that temperature can also affect the gain of weather radar antennas and most significantly the differential gain. These changes of gain cause the Zdr (differential reflectivity) bias to vary significantly. The temperature dependency of the Zdr bias has been shown for S-Pol (NCAR’s S-band research radar) PECAN (Plains Elevated Convection at Night) data and it was attributable to the antenna structure. This paper uses GRASP by TICRA Cooperation to model the S-Pol antenna and to investigate possible expansion and contraction mechanisms of the antenna that could cause the observed changes in Zdr bias. Data from S-Pol is used to illustrate the temperature dependent Zdr bias.