1. Broadly, a power ratio used in certain applications of radar that describes the degree to which the backscattered power from unwanted targets (clutter) is suppressed or canceled in one mode of measurement relative to another mode of measurement. It is defined to yield a value greater than unity or, equivalently, a positive decibel quantity. For example, in some applications it is defined as the ratio of signal intensity backscattered from rain observed with linear polarization to the signal intensity backscattered from rain observed with circular polarization. Values of 25–30 dB are typical of light rain observed at wavelengths of 3– 10 cm. 2. For a dual-channel radar, the ratio of the power received in the orthogonal channel to that received in the transmission channel for transmitted circular polarization. The stronger component of the target signal from precipitation is the component in the orthogonal channel because the sense of the circular polarization is reversed as its direction of propagation changes when it is scattered back toward the radar. 3. A ratio that describes the degree to which radar clutter is suppressed by a clutter filter. This usage applies particularly to moving-target indication (MTI) radars. Shrader and Gregers-Hansen recommend that the term “improvement factor” be used in place of “cancellation ratio” because the latter term has been used inconsistently. Compare circular depolarization ratio.