Target acquisition systems include the human eye, electrooptics (television sensors and display systems) radar, Forward Looking Infrared (FLIR) sensors, and laser seeker/tracker systems. Of these sensors, the human eye is the most capable of locating a target under most conditions. However, specific sensors can out-perform the human eye in some instances. For example, an electrooptical sensor adapted for low-light levels can out-perform the human eye at night under starlit skies, and a microwave system can out-perform the human eye because it can distinguish targets through clouds.

No matter what target acquisition system is used, the weapon must find its way to the target. This leads us into our next subject, which is Precision Guided Munitions (PGMs).

Learning Objective: Identify the two major components of precision guided munitions (PGMs).

PRECISION GUIDED MUNITIONS (PGMS)

After a target is located, PGMs are designed to accomplish two things: (1) to sense the difference between the electromagnetic radiation emitted or reflected by the target and that emitted or reflected by the targets surroundings, and (2) to guide the weapon to its target.

Two components make up the PGM; the guidance unit (seeker), and the control unit (tracker).

The guidance unit provides input to the control unit to guide or maneuver a PGM to a target. Electrooptical sensors are often used in these units and are most easily described as sophisticated television cameras. They can operate at visible wavelengths, infrared wavelengths, and at millimeter/microwave wavelengths. The sensor measures the reflected or emitted energy in its field of vision and converts it into electrical voltages. These voltages then drive electronic logic circuits that discriminate between the differences in a targets energy level and that of its surroundings. This ability to detect the contrast in energy levels is basic to any PGMs operation.

Two characteristics of guidance units are important from the viewpoint of environmental support: (1) each unit has a minimum energy contrast level. If this minimum level of energy contrast is not met, the logic circuits do not activate. The closer the targets temperature is to its surroundings, the more difficult it is for the unit to "lock on" the target. (2) guidance units can work only in limited energy ranges; too little energy cannot be detected, and too much energy saturates and can damage the sensor.

There are three types of guidance systems: active, semiactive, and passive.

ACTIVE. With an active guidance system a PGM emits radiation in the direction of the target, and the target reflects the energy back to the PGM. The guidance unit senses the reflected radiation and "homes in" on the reflected energy beam. Active guidance systems respond to reflected energy.  

SEMIACTIVE. A semiactive guidance system is much the same as an active system except that the reflected energy that the unit "homes in" on originates from another aircraft or from a source on the ground.

PASSIVE. Passive guidance systems home in on the naturally emitted or reflected energy contrast between a target and its background. In other words, passive systems distinguish thermal differences between the target and its surroundings.

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing