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Wireless sensor networks comprising nodes equipped with cameras have become common in many scenarios, providing valuable visual data for some relevant services such as localization, tracking, patterns identification and emergencies detection. In this context, algorithms and optimization approaches have been designed to perform different types of quality assessment or performance enhancement tasks, addressing challenging issues such as networking, compression, availability, reliability, security, energy efficiency and virtually any subject related to the operational challenges of those networks. However, the dynamics of coverage failures have not been properly modelled in visual sensor networks, resulting in unrealistic perceptions when optimizing or assessing quality in most visual sensing scenarios. Particularly, the Field of View of visual sensors will be affected by occlusion caused by obstacles in the monitored field, which may turn such sensors inadequate for the expected monitoring services of the considered network. Therefore, this article proposes a mathematical model to assess occlusion caused by mobile obstacles such as vehicles on a road or forklifts in an industrial plant, aiming at the selection of the visual sensor nodes that will not have their coverage significantly restricted by those obstacles. Doing so, the proposed model can be exploited by any optimization or quality assessment approach in wireless visual sensor networks, providing a preprocessing method when selecting visual nodes.

The first step of this research has been to discriminate, by means of a commercial electronic nose (e-nose), the maturity evolution of seven types of fruits stored in refrigerated cells, from the post-harvest period till the beginning of the marcescence. The final aim was to determine a procedure to select a reduced set of sensors that can be efficiently used to monitor the same class of fruits by a low cost system with few, suitable sensors without loss in accuracy and generalization. To define the best subset we have compared the use of a projection technique (the Principal Component Analysis, PCA) with the sequential feature selection technique (Sequential Forward Selection, SFS) and the Genetic Algorithm (GA) technique by using classification schemes like Linear Discriminant Analysis (LDA) and k-Nearest Neighbor (kNN) and applying two data pre-processing methods. We have determined a subset of only three sensors which gives a classification accuracy near 100%. This procedure can be generalized to other experimental situations to select a minimal and optimal set of sensors to be used in consumer applications for the design of ad hoc sensory systems.