The ratio of power received in the transmission channel to power received in the orthogonal channel of a dual-channel radar when a circularly polarized signal is transmitted. Because the stronger component of the circularly polarized signal backscattered from hydrometeors has a polarization orthogonal to the transmitted polarization, the circular depolarization ratio yields a value less than unity or, equivalently, a negative decibel quantity. Note that relative to the receiver channels of the radar, the circular depolarization ratio is defined inversely to the linear depolarization ratio. Compare cancellation ratio.