Primarily in military context, but also in industrial and general engineering systems that must respond to objects that are not always present, target acquisition is the set of discipline that allows a system that operates on specific objects to begin its processing. The target acquisition may be completely cooperative between a "master" response system, such as an air traffic control systems based on transponders. It may be completely under the control of the response system, as with storm detection in weather forecasting. It may involve a target actively using electronic warfare methods to interfere with acquisition and subsequent tracking and handling decisions.
A great variety of technologies are involved; their selection depends on the needed range, discrimination among targets, the means by which a control system can detect the object), and the level of interactions among possibly multiple objects and response systems. For example, long range is often highly undesirable, in such applications as multiple parallel retail store checkout lines. Having acquisition ranges longer than 1 meter/39.34 inches could well cause a single purchased object to be acquired by more than one cash register.
In other applications, such as ballistic missile defense, long range is highly desirable; the farther away the target can be acquired, the longer the decision time on what to do about it and the longer the time to deploy reactions to it.