**Seung Hyo Park, Sa Yong Chong, Hyung June Kim and Taek Lyul Song \***

Department of Electronic Systems Engineering, Hanyang University, Ansan 15588, Korea; gyeonwoo4@naver.com (S.H.P.); syong0329@hanmail.net (S.Y.C.); lovesunday88@naver.com (H.J.K.) **\*** Correspondence: tsong@hanyang.ac.kr; Tel.: +82-31-400-4156

Received: 10 December 2019; Accepted: 21 December 2019; Published: 23 December 2019

**Abstract:** The point detections obtained from radars or sonars in surveillance environments include clutter measurements, as well as target measurements. Target tracking with these data requires data association, which distinguishes the detections from targets and clutter. Various algorithms have been proposed for clutter measurement density estimation to achieve accurate and robust target tracking with the point detections. Among them, the spatial clutter measurement density estimator (SCMDE) computes the sparsity of clutter measurement, which is the reciprocal of the clutter measurement density. The SCMDE considers all adjacent measurements only as clutter, so the estimated clutter measurement density is biased for multi-target tracking applications, which may result in degraded target tracking performance. Through the study in this paper, a major source of tracking performance degradation with the existing SCMDE for multi-target tracking is analyzed, and the use of the clutter measurement probability is proposed as a remedy. It is also found that the expansion of the volume of the hyper-sphere for each sparsity order reduces the bias of clutter measurement density estimates. Based on the analysis, we propose a new adaptive clutter measurement density estimation method called SCMDE for multi-target tracking (MTT-SCMDE). The proposed method is applied to multi-target tracking, and the improvement of multi-target tracking performance is shown by a series of Monte Carlo simulation runs and a real radar data test. The clutter measurement density estimation performance and target tracking performance are also analyzed for various sparsity orders.

**Keywords:** data association; clutter measurement density; spatial clutter measurement density estimator; multi-target tracking
