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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 be 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. 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. ==Basic concept== 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. As the camera scans the image, the brightness of the location currently being scanned is represented as a voltage. The series of varying voltages forms an amplitude modulated (AM) signal that encodes the brightness variations along any given line, and spikes of 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. These rapid changes trigger circuitry that sends the voltage of the television's horizontal and vertical deflection magnet drivers into capacitors. Thus the capacitors store a value representing the Y and X locations of any high contrast spot within the image. The missile is initially brought onto the target manually, normally using a small cueing input on the pilot's control stick or by the weapons officer in two-seat aircraft. When the trigger is pressed to ''pickle'' the target, the timers trigger on a bright spot near the center of the image, and that time is written to an analog memory. Normally the recorded spot is indicated on the screen in the cockpit and the pilot can select other high-contrast spots within the image, in an attempt to select one that is either the target or very close to it. From then on the contrast trigger circuits fire only for signals close to that X and Y location, filtering out other objects. Once a suitable target image has been selected, the seeker enters tracking mode. As the television scanning process continues, the contrast triggers continually produce new X and Y locations that are compared to the ones in the memory. The difference between the voltages gives an X and Y error, which is used by the seeker's gimbal mounting to turn the camera so it re-aligns with the original location. The guidance system then compares the angle of the camera to the angle of the missile body, and sends commands to the aerodynamic controls to bring it back onto a collision course. To address the need to track moving targets, a proportional navigation system is normally used, which naturally produces the required "lead". 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Contrast seeker」の詳細全文を読む スポンサード リンク
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