Sunspike Detection using Radial-by-Radial Noise Estimates

Sunspikes, or the incidental intersection of the radar receive path with the sun's radio emissions, are an integral part of the core methods used by the Radar Operations Center to calibrate the Differential Reflectivity of the WSR- 88D fleet. A method had been developed within the Radar Operations Center for post processing the Level II data to find instances of these sunspikes. This method relied on using the sun's geophysically referenced position in tandem with the derived SNR from reflectivity values to determine if a direct sunspike is observed. After the release of Software Build 14 and attendant introduction of Radial-by-Radial Noise Estimation, this method became untenable. Noise from the sun censors the sunspike reflectivity signature, as it raises the noise floor at the sunspike radial. As such, Radial-by-Radial noise estimates replaced the SNR estimates from reflectivity within the algorithm. This led to the introduction of unwanted weak sunspike instances, which were invariant in elevation as compared with results the previous reflectivity method yielded. This paper explains how the algorithm was corrected, and the extra data pared. A proxy for SNR was found. This proxy was the ratio of the peak sunspike noise to the legacy Blue-Sky noise, which was used as the global noise value before Radial-by-Radial Noise was introduced. It has been shown that this ratio is representative of SNR, and it can be used to filter the data. Henceforth, this ratio will be referred to as SPNR (Sunspike Noise Ratio or Spike Noise Ratio).