This paper presents an unsupervised synthetic aperture radar (SAR) image change detection method based on improved bilateral filtering and fuzzy C means (FCM). Many previous approaches to change detection are based on a difference image. Unlike conventional approaches, based on difference images, our method demonstrates superior ability to reduce speckle noise and suppress background information, while still retaining edge information effectively. First, the two images are preprocessed using a Lee filter to remove some of the speckle noise. Second, we use the neighbor-log ratio and the Gauss-log ratio to produce initial change maps. Third, we use the improved bilateral to fuse the two change maps, to obtain an initial difference image. Next, we apply a median filter on the initial difference image, to obtain the final difference image. The above method makes full use of the field information, and it can effectively remove speckle noise while still preserving edge information. Finally, an improved FCM algorithm is used to cluster the denoised difference image. Denoising prior to clustering overcomes the main deficiency of conventional clustering algorithms, which is that they are noise sensitive. Empirical experiments, on three groups of SAR images, suggest that the proposed algorithm outperforms several other methods from the literature, in terms of noise suppression, accuracy, and lower change detection error rates.
KEYWORDS: Acoustics, Signal to noise ratio, Signal detection, Interference (communication), Electronic filtering, Target detection, Environmental sensing, Sensors, Linear filtering, Detection and tracking algorithms
Stevens Institute of Technology is performing research aimed at determining the acoustical parameters that are necessary for detecting and classifying underwater threats. This paper specifically addresses the problems of passive acoustic detection of small targets in noisy urban river and harbor environments. We describe experiments to determine the acoustic signatures of these threats and the background acoustic noise. Based on these measurements, we present an algorithm for robustly discriminating threat presence from severe acoustic background noise. Measurements of the target's acoustic radiation signal were conducted in the Hudson River. The acoustic noise in the Hudson River was also recorded for various environmental conditions. A useful discriminating feature can be extracted from the acoustic signal of the threat, calculated by detecting packets of multi-spectral high frequency sound which occur repetitively at low frequency intervals. We use experimental data to show how the feature varies with range between the sensor and the detected underwater threat. We also estimate the effective detection range by evaluating this feature for hydrophone signals, recorded in the river both with and without threat presence.
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