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Moving target indication (MTI) is a mode of operation of a radar to discriminate a target against the clutter. [1] It describes a variety of techniques used for finding moving objects, like an aircraft, and filter out unmoving ones, like hills or trees.
Range ambiguity occurs when the time taken for an echo to return from a target is greater than the pulse repetition period (T); if the interval between transmitted pulses is 1000 microseconds, and the return-time of a pulse from a distant target is 1200 microseconds, the apparent distance of the target is only 200 microseconds.
Doppler shifting of the returned signals is a function of the radar carrier frequency, as well as the speed of the radar source and target, with positive Doppler shift from surfaces moving toward the illuminator and negative shift of surfaces moving away from it. Moving surfaces impose a pulse width modulation.
Radial velocity aliasing occurs when reflections arrive from reflectors moving fast enough for the Doppler frequency to exceed the pulse repetition frequency (PRF). Frequency ambiguity resolution is required to obtain the true radial velocity when the measurements is made using a system where the following inequality is true.
Areas outside the blue zones are blind ranges and blind velocities, which are filled in using multiple PRF and frequency agility. The unambiguous zone is in the lower left corner. All of the other blocks have ambiguous range or ambiguous radial velocity. Pulse Doppler radar relies on medium pulse repetition frequency (PRF) from about 3 kHz to ...
The pulse-repetition frequency (PRF) is the number of pulses of a repeating signal in a specific time unit. The term is used within a number of technical disciplines, notably radar . In radar, a radio signal of a particular carrier frequency is turned on and off; the term "frequency" refers to the carrier, while the PRF refers to the number of ...
The simplest method is available when the apparent size of the target is relatively small with respect to clutter source. In this case the reduced pulse and beam width, which matches the expected target size, may produce good signal-to-noise ratio (target to clutter ratio). Additional discrimination capabilities rely on target imaging or ...
A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity.