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RF is a rate of oscillation in the range of around 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations. The determination of the object's position, velocity and other characteristics, or the obtaining of information relating to these parameters by the transmission of radio waves and reception of their return is sometimes referred to as radiodetermination. For example, radar operates by generating pulses of radio frequency energy and transmitting these pulses via a directional antenna. When a pulse impinges on an object in its path, a small portion of the energy is reflected back to the antenna. The radar is in the receive mode in between the transmitted pulses, and receives the reflected pulse if it is strong enough. The radar indicates the range to the object as a function of the elapsed time of the pulse traveling to the object and returning. The radar indicates the direction of the object by the direction of the antenna at the time the reflected pulse was received.

The "radar equation" mathematically describes the process and may be used to determine maximum range as a function of the pulse width (PW) and the pulse repetition rate (PRR). In most cases, narrow pulses with a high PRR are used for short-range, high-resolution systems, while wide PW's with a low PRR may be used for long-range search. In general, a higher gain (larger aperture) antenna will give better angular resolution, and a narrower pulse width will give better range resolution. The key to modern radar systems is the digital computer and its data processing capability which can extract a vast amount of information from the raw radar signals and present this information in a variety of graphic and alphanumeric ways on displays as well as feeding it direct to weapon systems. It also enables the systems to carry out many more tasks such as target tracking and identification. In addition, modern signal processors provide adaptive operation by matching the waveform to the environment in which the radar is operating.

The grouping of Acoustic and Seismic is natural, as there is an overlap at low frequencies (~20-200 Hz) where there is sensitivity in both types of sensors. Acoustic sensors are typically pressure based and seismic sensors are typically accelerometers. Magnetic and EM might have been more naturally grouped with electro-optics, as there is a continuum on that spectrum, however, inclusion with acoustics makes sense from an application perspective, as acoustics and magnetics are primary sensing modalities for submarine and buried object detection.

EO/IR systems includes active and passive. The wavelength region for optical radiation spans from approximately 100 nanometers (nm) to 1000 micrometers (um). The optical radiation spectrum can be broken up into three basic regions: ultraviolet (UV) from 100nm - 400 nm; visible from 400 nm - 760 nm; and IR from 760 nm - 1000 um. These regions are dependent on the reflection of the target by sunlight or moonlight or the target's own emission of radiation. Radiation energy coming from the target and background is primarily reflective in the visible through short wave IR changing to a mixture of reflective and emissive in mid-wave IR. Long wave IR imaging relies on thermal emission of radiation from targets and background. Additionally, EO/IR photons travel through a medium, the atmosphere, which can refract, absorb, or scatter them. What has changed dramatically is the method and speed of processing the imagery, the amount of information that can be obtained, and the way that the information is displayed to the operator.

* Sensor Processing is an element of all areas

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