to those used by radio navigation satellite systems, such as GPS, Global Navigation Satellite System, Galileo, and the Computerized Movement Planning and Status System. Generally, four transmitter sources are needed to determine location in three dimensions and account for time, yielding absolute position. Frequency diversity is also required to minimize multipath effects on geolocation performance.

Life signs monitoring is considered separate from through-the-wall target monitoring. A sensor is used to determine the life and health status of a fallen comrade. This technology can help protect members of the squad during a firefight or in other compromising situations. One approach is to use mmw radar to detect respiration. Depending on the range to the target, mmw radar can also be used to detect and calculate heart rate. LADAR detects respiration but not heart rate.

The above discussion suggests the need for multiple sensor assets operating over different frequency regimes. Identifying and developing multipurpose sensor packages (e.g., a single aperture to provide both radar and SIGINT capabilities; or, a single sensor for concealed weapons detection, life signs monitoring, and navigation) would be highly desirable.

Force Protection

The primary force protection objectives (Table G-2) include the following:

•   Perimeter surveillance for encampments;

•   Early warning for incoming rockets, artillery, and mortars;

•   Counter improvised explosive device (CIED);

•   Fire/sniper location; and

•   CBRN and explosives detection.

Life signs monitoring and concealed weapons detection fall in both domains, SA and force protection.

Perimeter surveillance provides early warning of an attack on an encampment. Radar, acoustics, and infrared (IR) sensors are likely sensor technology choices. Radar and acoustic sensors search for Doppler-shifted returns indicative of motion in the vicinity of the encampment; dismount targets have a very specific radar and acoustic signature, a “whoomping” sound, predominantly due to torso motion (the radar signal can be converted to an acoustic output, and this is sometimes done in perimeter surveillance radar systems).

Early warning against rockets, artillery, and mortars is commonly the domain of WLR systems. WLR systems first detect the incoming threat and provide a warning. Then they calculate a counterfire solution based on the threat type and trajectory. IRST sensors can also be used; however, the false alarm rate in occupied environments (e.g., urban environments with dense traffic backgrounds) is a bigger concern than it is for radar. Active protection systems calculate the presence of an incoming threat and then deploy a kinetic kill

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