Detection of signals in noise

Noise is the unwanted energy that interferes with the ability of the receiver to detect the wanted signal. It may enter through the antenna along with the desired signal or it may be generated within the receiver itself. In underwater sonar systems, external acoustic noise is generated by waves and wind on the water surface, by biological agents (fish, prawns, etc.), and by man-made sources such as engine noise. In radar and lidar sensors the external electromagnetic noise is generated by various natural mechanisms such as the sun and lightning, among others. Man-made sources of electromagnetic noise are myriad, from car ignition systems and fluorescent lights to other broadcast signals. The deliberate transmission of noise in an attempt to mask a target echo or otherwise deceive a sensor is known as jamming.