On the spatial and multi-frequency airborne ultrasonic image fusion

Single and fixed airborne ultrasonic frequency images are presented and used in many application areas, such as in medicine, industrial processes, for monitoring and fault detection and diagnosis. Airborne ultrasonic images have poor information content, mainly because of the transducers' uncertainty and the high absorption of ultrasounds in the air. This is the reason why we need some transformations, e.g. fusion, in order to enrich the information content of such images. Two fusion processes are considered: (i) a spatial process involving the images from the left and right sides; (ii) a multi-frequency fusion process involving images obtained at various ultrasonic frequencies. The fusion process depends on the quantitative criterion, as well as on the qualitative opinion of end-users. In order to meet real-time requirements and small computation resources, imposed by the navigation tasks based on ultrasonic images, the fusion rules should follow the fastest rules, e.g. the fusion rules based on the weighted average of available sources. The obtained results by computer simulation show that the optimum set of weights, from the imposed cost criterion based on similarity and dissimilarity of images, has a distribution which is inversely proportional to ultrasonic frequency. The fusion of multi-frequency images that generates color image is presented, as exploratory research direction. The obtained fused images are more appropriate for detection and classification of the explored targets in sonar based applications.