38,205 research outputs found
Novelty detection in video surveillance using hierarchical neural networks
Abstract. A hierarchical self-organising neural network is described for the detection of unusual pedestrian behaviour in video-based surveillance systems. The system is trained on a normal data set, with no prior information about the
scene under surveillance, thereby requiring minimal user input. Nodes use a trace activation rule and feedforward connections, modified so that higher layer nodes are sensitive to trajectory segments traced across the previous layer. Top layer nodes have binary lateral connections and corresponding ânovelty accumulatorâ nodes. Lateral connections are set between co-occurring nodes, generating a signal to prevent accumulation of the novelty measure along normal sequences. In abnormal sequences the novelty accumulator nodes are allowed to increase their activity, generating an alarm state
Hierarchical self organizing map and focusing inspection strategy for mobile robot novelty detection
Novelty detection is a process of recognizing changes based on learned knowledge.
In this research, a novelty detection system was implemented on a mobile robot with an
array of sonar sensors for surveillance application. In order to perform novelty detection, a
map that stores normal information with respect to any particular robot pose in an
environment is required. The map is needed to detect changes and determine the position
of novel event. The challenges of mobile novelty detection system are that the false
positive rate is usually high whereas the true positive rate is usually low due to mapping
and monitoring problems. During mapping, errors due to robot localization and sensor
measurement can reduce the quality of the map built. However, available methods in
mapping assume perfect localization, hence error in localization is not taken into account
in the process of mapping. During monitoring, inspection interval that is too small will
consume a lot of time and energy but if the interval is too big, novelty could be missed,
hence lower the true positive detection. On top of that, low true positive detection is also
caused by the low reliability of sonar sensor measurement. Thus, the objective of this
thesis is to utilize mobile novelty detection system by developing a mapping and
monitoring strategy that has low false positive detection, high true positive detection and
able to estimate the position of a novelty. This thesis proposed two methods regarding to
mapping and monitoring process; a hierarchical Self Organizing Map (SOM) and a
Focusing Inspection Strategy (FIS). Unlike other mapping methods, hierarchical SOM also
consider localization error when associating the normal information with respect to the
robot pose. FIS is a multi resolution monitoring strategy which works by changing the
frequency of measurement depending on the detection of anomaly. In this thesis, two
models were considered; a step (FS) and linear (FL) resolution models. The hierarchical
SOM was validated by using simulation and experimentation of the inspection in
environment with normal and novel event. False positive rate is measured to determine the
map performance. The results show that hierarchical SOM is able to map the normal
condition of the environment very well. The inspection results show the false positive rate
occurred less than 0.1 at the higher sensitivity setting of 0.9 in either normal or novel
condition. The performance of FIS was investigated by using experimentation of the
inspection of novel objects of different sizes. The results show that by changing the
frequency of measurement using the FS and FL models, the number of true positive
detection increases up to 80% when compared to inspection with fix measurement
frequency. FIS also reduced the error of position estimation by about 8.8% and 10.9% each
for FS and FL and maintained the false positive rate lower than 0.1
A Neural System for Automated CCTV Surveillance
This paper overviews a new system, the âOwens
Tracker,â for automated identification of suspicious
pedestrian activity in a car-park.
Centralized CCTV systems relay multiple video streams
to a central point for monitoring by an operator. The
operator receives a continuous stream of information,
mostly related to normal activity, making it difficult to
maintain concentration at a sufficiently high level.
While it is difficult to place quantitative boundaries on
the number of scenes and time period over which
effective monitoring can be performed, Wallace and
Diffley [1] give some guidance, based on empirical and
anecdotal evidence, suggesting that the number of
cameras monitored by an operator be no greater than 16,
and that the period of effective monitoring may be as
low as 30 minutes before recuperation is required.
An intelligent video surveillance system should
therefore act as a filter, censuring inactive scenes and
scenes showing normal activity. By presenting the
operator only with unusual activity his/her attention is
effectively focussed, and the ratio of cameras to
operators can be increased.
The Owens Tracker learns to recognize environmentspecific
normal behaviour, and refers sequences of
unusual behaviour for operator attention. The system
was developed using standard low-resolution CCTV
cameras operating in the car-parks of Doxford Park
Industrial Estate (Sunderland, Tyne and Wear), and
targets unusual pedestrian behaviour.
The modus operandi of the system is to highlight
excursions from a learned model of normal behaviour in
the monitored scene. The system tracks objects and
extracts their centroids; behaviour is defined as the
trajectory traced by an object centroid; normality as the
trajectories typically encountered in the scene. The
essential stages in the system are: segmentation of
objects of interest; disambiguation and tracking of
multiple contacts, including the handling of occlusion
and noise, and successful tracking of objects that
âmergeâ during motion; identification of unusual
trajectories. These three stages are discussed in more
detail in the following sections, and the system
performance is then evaluated
A survey of outlier detection methodologies
Outlier detection has been used for centuries to detect and, where appropriate, remove anomalous observations from data. Outliers arise due to mechanical faults, changes in system behaviour, fraudulent behaviour, human error, instrument error or simply through natural deviations in populations. Their detection can identify system faults and fraud before they escalate with potentially catastrophic consequences. It can identify errors and remove their contaminating effect on the data set and as such to purify the data for processing. The original outlier detection methods were arbitrary but now, principled and systematic techniques are used, drawn from the full gamut of Computer Science and Statistics. In this paper, we introduce a survey of contemporary techniques for outlier detection. We identify their respective motivations and distinguish their advantages and disadvantages in a comparative review
Applied Sensor Fault Detection, Identification and Data Reconstruction
Sensor fault detection and identification (SFD/I) has attracted considerable attention in military applications, especially when safety- or mission-critical issues are of paramount importance. Here, two readily implementable approaches for SFD/I are proposed through hierarchical clustering and self-organizing map neural networks. The proposed methodologies are capable of detecting sensor faults from a large group of sensors measuring different physical quantities and achieve SFD/I in a single stage. Furthermore, it is possible to reconstruct the measurements expected from the faulted sensor and thereby facilitate improved unit availability. The efficacy of the proposed approaches is demonstrated through the use of measurements from experimental trials on a gas turbine. Ultimately, the underlying principles are readily transferable to other complex industrial and military systems
Hybrid HC-PAA-G3K for novelty detection on industrial systems
Piecewise aggregate approximation (PAA) provides a powerful yet computationally efficient tool for dimensionality reduction and feature extraction. A new distance-based hierarchical clustering (HC) is now proposed to adjust the PAA segment frame sizes. The proposed hybrid HC-PAA is validated by a generic clustering method âG3Kmeansâ (G3K). The efficacy of the hybrid HC-PAA-G3K methodology is demonstrated using an application case study based on novelty detection on industrial gas turbines. Results show the hybrid HC-PAA provides improved performance with regard to cluster separation, compared to traditional PAA. The proposed method therefore provides a robust algorithm for feature extraction and novelty detection. There are two main contributions of the paper: 1) application of HC to modify conventional PAA segment frame size; 2) introduction of âG3Kmeansâ to improve the performance of the traditional K-means clustering methods
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