What characterizes the signals that are considered clutter in RADAR?

Clutter in RADAR specifically refers to unwanted signals that can interfere with the detection of actual targets. These signals often arise from environmental factors such as terrain, weather, or other non-target objects that scatter the RADAR waves. Clutter can mask or distort the true signals generated by objects of interest, making it difficult to accurately identify or track them.

In contrast, the other choices describe characteristics of signals that are beneficial in some way or related to the targets being monitored. For instance, identifying an object's velocity is crucial for understanding its movement but does not describe clutter. Similarly, indicating the presence of an object or providing supplementary information pertains to useful signals that contribute positively to the RADAR's functioning rather than introducing confusion or interference. Therefore, the defining property of clutter is that it acts as a disruptive element rather than a helpful aspect of RADAR signal interpretation.