EUROPEAN MICROWAVE ASSOCIATION Radar detection and track in presence of impulse interference by using the polar hough transform Ivan Garvanov 1 and Christo Kabakchiev 2 Abstract – In this paper, the polar Hough transform (PHT) is con- sidered as a track initiator in a track before detect (TBD) sys- tem. The study is performed in the presence of impulse inter- ference. The algorithm under study includes a parametric CFAR detector, which works successfully in conditions of impulse in- terference and uses the polar Hough transform. The proposed Hough detector improves the detection probability in conditions of both Poisson and binominal random impulse flows. The us- age of both CFAR and Hough transforms materially reduces the requirements to the input SNR in conditions of impulse noise. Another important advantage of PHT is that it is stability when the target velocity and azimuth vary in the time. Index Terms – Radar signal processing, Polar Hough transform, Track before detect, CFAR processor, Binary integration, Ran- domly arriving impulse interference. I. Introduction The standard Hough transform and the related Radon transform have aroused much interest in recent years. The use of them makes possible the transformation of two- dimensional images with lines into a domain of possi- ble line parameters, where each image line corresponds to a peak, positioned at the respective line parameters. For these reasons, many line detection applications are considered within the image processing, computer vision and seismic research areas. Firstly, the use of the standard Hough transform (SHT) for target detection and track de- termination in white Gaussian noise is introduced by Carl- son in [1]. The presence of randomly arriving impulse interference in the radar resolution cells can cause drastic degradation in the performance of a CFAR processor, and of the SHT de- tector. False alarms resulted from that make difficult the track detection. The improvement in the target detection and trajectory detection on the non-homogeneous back- ground (impulse interference) is possible by using an ap- proach for CFAR detection by means of the HT [2-4]. The Hough detection scheme includes a CFAR detector for sig- nal detection in the scan area, the HT for mapping the tar- get distance measurements from the scan area into the pa- rameter space, binary integration of data in the parameter space and linear trajectory detection. These CFAR Hough detectors have been studiedin cases when the target moves in the same azimuth cell and the target velocity is constant [2-6]. There are modifications where the HT is used for the image processing after the conversion of radar data from the range-azimuth coordinate system to the Cartesian sys- tem associated with radar [7-9]. A polar Hough (PH) transform, which is more suitable for search radar applications, is proposed in [10]. This trans- form is analogous to the standard Hough transform, where the input parameters are the target distance and azimuth measured by search radar. The technique converts the data obtained from previous search scans into one large multi- dimensional polar data map. This transform is suitable in radar detection and track determination, when both the tar- get velocity and the target azimuth vary in time. The possibility to minimize time of radar signal detection providing the required values of the probabilities of false alarm and detection has appeared in result of the sequential analysis that has been developed in [11]. The priority of the sequential detector over the conventional detector is in the radar energy reduction at the stage of target detection. In this paper, a new CFAR polar Hough detector that can be used in a TBD system in conditions of randomly ar- riving impulse interference is proposed and evaluated. In this two-stage detector, the Hough detector removes all false alarms, which are resulted from the CFAR detector. The general structure of an adaptive polar Hough detec- tor with binary integration is similar to that of a standard Hough detector. The difference between them is that the polar detector uses (range-azimuth-time) space while the SHT employs (range-time) space. The detection probabil- ity of a polar Hough detector can be calculated by Brun- ner’s method as for a standard Hough detector. In our previous algorithms described in [2-6], the use of the PHT instead of the SHT for track and target detection in the presence of randomly arriving impulse interference, allows employing them in real practical situations when the target moves with variable velocity along arbitrary lin- ear trajectories. II. Signal model It is assumed that the target is fluctuating according to the Swerling II case. It is also assumed that the total back- ground environment includes the binomial distribution of impulse interference-plus-noise situation. The Binomial model describes a situation when the impulse noise is de- rived from two independent and identical impulse-noise sources, each of which generates a random impulse se- quence with the same power intensity and the same av- erage repetition frequency [12]. The probability of occur- Received December 8th, 2006. Revised April 6th, 2007. Institute of Information Technologies (IIT), Bulgarian Acad- emy of Science. Bulgaria, Sofia 1113, Akad. G. Bonchev Str,. bl.2. Phone: +359 29792928; E-mail: 1 igarvanov@iit.bas.bg; 2 ckabakchiev@iit.bas.bg Proceedings of the European Microwave Association Vol. 3; March 2007; 170–175