Published in IET Signal Processing Received on 18th April 2008 Revised on 28th October 2008 doi: 10.1049/iet-spr.2008.0068 ISSN 1751-9675 Target tracking with two passive infrared non-imaging sensors Z.M. Djurovic 1 B.D. Kovacevic 1 G.D. Dikic 2 1 Faculty of Electrical Engineering, University of Belgrade, Bulevar kralja Aleksandra 73, 11000 Belgrade, Serbia 2 Military Technical Academy, Ratka Resanovica 1, 11133 Belgrade, Serbia E-mail: zdjurovic@etf.bg.ac.yu Abstract: A new solution for target tracking in air space with two infrared (IR) sensors is presented. The principle of triangulation is used as a basic method for range estimation. However, when the target directions are nearly collinear relative to the baseline, this method produces unacceptable results. The problem is solved by introducing the ratio of IR energy adsorbed at the end of a baseline in a measurement vector within the extended Kalman filter type target state estimator. Also, a recursive estimator for the extinction coefficient that describes the influence of the atmosphere is designed. This combination results in a new adaptive structure for simultaneous estimation of target kinematic states and atmospheric parameters. Such a structure performs much better than the standard triangulation method, yielding acceptable results even in the case where target directions are close to the baseline. Simulation and experimental results demonstrate the feasibility and limitations of the proposed approach. 1 Introduction Target tracking and detection in modern combat systems is based on active radar sensing and laser illumination. However, an active sensor can be detected from a considerable distance and destroyed by homing missiles. The use of passive infrared (IR) sensors can be a better solution for a real situation on the battlefield [1]. Passive IR sensors are recognised as providing a precise bearing- only target location. Range information can also be extracted through fusion of data from two or more such sensors. An overview of the existing literature devoted to these topics suggests two main approaches. One of them is to design efficient data fusion obtained from the sensor network [2, 3], while the other addresses the synthesis of intelligent algorithms for non-measurable distance estimation based on measurable angles [4]. In a case where only two passive sensors are used (the so- called single baseline method), there is a direction in which all precision in the triangulated target range is lost. This phenomenon is known as ‘geometric dilution of precision’. A possible approach to overcoming this effect results in a dual baseline scheme [5]. In this approach, the baselines have been set as orthogonal, so that the individual performance of each of the baselines follows the mathematics of the single baseline model. Moreover, the performance of each baseline is peaked along the corresponding direction for geometric dilution of the alternative baseline. Thus, it is possible to eliminate the geometric dilution problem by switching between baselines at performance crossing points. It can be shown that the crossover points depend primarily on the ratio of the two baseline lengths [5]. Consequently, four IR sensors must be used in order to implement the proposed dual baseline scheme. This scheme is especially suitable for implementation in shipborne systems. In ground-to-air scenarios, a solution with three IR sensors placed at the corners of a triangle can be applied. Additionally, in the early 1960s, several patents were approved which related a ‘hot’ target’s IR signal attenuation to range [6, 7]. Both of these schemes applied the principle that the ratio of signal attenuation in two narrow IR bands, with known but nominally different atmospheric attenuation coefficients, could be related to range. However, both methods required prior knowledge of the target’s IR spectrum, an assumption that can be easily disqualified with today’s counter-measure tactics. In this paper, a new method IET Signal Process., 2009, Vol. 3, Iss. 3, pp. 177–188 177 doi: 10.1049/iet-spr.2008.0068 & The Institution of Engineering and Technology 2009 www.ietdl.org