Contrast seeker

Optical contrast seekers, or simply contrast seekers, are a type of missile guidance system using a television camera as its primary input. The camera is initially pointed at a target and then locked on, allowing the missile to fly to its target by keeping the image stable within the camera's field of view.

The first production missile to use a contrast seeker was the AGM-65 Maverick, which began development in the 1960s and entered service in 1972. The system has not been widely used, as other guidance technologies like laser guidance and GPS have become more common, but the same basic concept is used in cameras to track objects, including the systems used to aim the laser designators.

Contrast seekers should be distinguished from television guidance systems, in which a live television signal is broadcast to the launch platform, which then uses manual direction to attack the target. Examples of TV guidance include the Martel and AGM-62 Walleye. The term "contrast contour" is sometimes used, but this may be confused with TERCOM systens.

Analog television cameras scan an image as a series of horizontal lines that are stacked vertically to form a grid or "frame". The camera's progression through the frame is carefully controlled by electronic timers, known as time base generators, that produce smoothly increasing voltages. As the camera scans the image, the brightness of the location currently being scanned is also represented as a voltage. The series of varying voltages from the sensor forms an amplitude modulated (AM) signal that encodes the brightness variations along any given scan line, and spikes in the signal indicate when the line or frame changes.

The contrast seeker is a simple device that can be implemented using very basic analog electronics. It first uses some form of automatic gain control to adjust the image brightness until it contains some areas with high-contrast spots. This produces a bias voltage signal to represent the background brightness level, making brighter objects stand out. Any rapid change in contrast along a given scan line causes the voltage from the camera to suddenly change. If the change is greater than a selected threshold, it triggers a second circuit that sends the output of the scanning time base generator into capacitors. Thus the capacitors store a voltage value representing the Y and X locations of any high contrast spot within the image.

...
Wikipedia