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CFAR DetectionCFAR detection is a classical technique of radar detection. In a radar system, if the detection threshold V_{T} is set as a constant value, the falsealarm rate Pf_{a} will rise with the increase of interference r: In a radar system, there are not only the thermal noise within the receiver, but also the interferences from the clutter and the enemy. These interferences are strong in most situations, and their amplitudes vary in different scenes. In that case, the falsealarm rate will not be constant any more. The method to keep a constant falsealarm rate is called CFAR detection [6]. With the development of radar detection, many CFAR detection methods are invented [713]. In practical applications, the specific method must be chosen according to the echo distribution. In a lowresolution SAR system, the amplitude of the echo obeys the Rayleigh distribution, while the amplitude of the echo obeys other distributions such as Swerling model [14], lognormal model [15] and v^{2 }distribution. In most SAR data, the Rayleigh distribution assumption is convincing, so the classical CACFAR algorithm in Rayleigh distribution is introduced in this section. Suppose the probability distribution function of clutter y is expressed as
Let x = rr, V_{0} = VT, and substitute them into Eq. 2.4.4, it yields
For the new clutter, the falsealarm rate follows Eq. 2.4.6, which is not related to the clutter. The relationship between the derivation r and the mean i is
The principle of CACFAR is illustrated in Fig. 2.8. Fig. 2.8 Principle of CACFAR detection 
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