**4. Performance Evaluation**

During the *<sup>p</sup>*-th scan, the current tracks, which can be described by mean **<sup>x</sup>**ˆ*p*|*<sup>p</sup>* and covariance **<sup>p</sup>***p*|*p*, are updated by using the current observations. All observations, which lie outside the validation gates % **y***c <sup>p</sup>*,*<sup>i</sup>* <sup>−</sup> **<sup>y</sup>**<sup>ˆ</sup> *<sup>c</sup> p* & **S***c p* −<sup>1</sup> % **y***c <sup>p</sup>*,*<sup>i</sup>* <sup>−</sup> **<sup>y</sup>**<sup>ˆ</sup> *<sup>c</sup> p* & > γ, are considered as irrelevant observations. Any irrelevant observation is processed by the track initiation module, where tentative tracks are formed based on the observations from two successive scans, that is, a window spanned by the maximum expected target velocity over a scan period selects all possible pairs of observations from two successive scans. Consequently, the observation pairs form tentative tracks by using the two-point initiation technique [35].

An initial target existence probability *P* χ*p* -- -**Z***p* will be assigned to all new tracks. All tracks can be updated recursively by using a new measurement set, the corresponding probabilities of target existence are updated too. During the tracking procedure, the probabilities of target existence are evaluated against specific thresholds for track confirmation and termination. A track exists if its probability of target existence is greater than the predefined threshold of track confirmation. A track disappears if its probability of target existence is below the predefined threshold of track termination. Multiple tracks, which are close to each other, would be combined into a single track. Only the confirmed tracks are displayed to the observer. We evaluate multi-target tracking performance based on the three criteria as follows:

A. Number of confirmed true tracks (NCTT) and Number of confirmed false tracks (NCFT)

A track in correspondence of the true state of a target can be considered as a true track. The *j*-th track denoted by mean **x**ˆ *j p*|*p* and covariance **p***<sup>j</sup> p*|*p* has relation with the *j*-th target state **x***<sup>j</sup> <sup>p</sup>*, a constant threshold <sup>ψ</sup> is employed to satisfy % **x**ˆ *j <sup>p</sup>*|*<sup>p</sup>* <sup>−</sup> **<sup>x</sup>***<sup>i</sup> p* & % **p***j p*|*p* &−1% **x**ˆ *j <sup>p</sup>*|*<sup>p</sup>* <sup>−</sup> **<sup>x</sup>***<sup>i</sup> p* & ≤ ψ. On the contrary, a track that does not associate with any true target state can be viewed as a false track. NCTT and NCFT are important measures for the multi-target tracking performance.
