Abstract
Underwater acoustic and optical data fusion has been developed in recent decades. Matching of underwater acoustic and optical images is a fundamental and critical problem in underwater exploration because it usually acts as the key step in many applications, such as target detection, ocean observation, and joint positioning. In this study, a method of matching the same underwater object in acoustic and optical images was designed, consisting of two steps. First, an enhancement step is used to enhance the images and ensure the accuracy of the matching results based on iterative processing and estimate similarity. The acoustic and optical images are first pre-processed with the aim of eliminating the influence of contrast degradation, contour blur, and image noise. A method for image enhancement was designed based on iterative processing. In addition, a new similarity estimation method for acoustic and optical images is also proposed to provide the enhancement effect. Second, a matching step is used to accurately find the corresponding object in the acoustic images that appears in the underwater optical images. In the matching process, a correlation filter is applied to determine the correlation for matching between images. Due to the differences of angle and imaging principle between underwater optical and acoustic images, there may be major differences of size between two images of the same object. In order to eliminate the effect of these differences, we introduce the Gaussian scale-space, which is fused with multi-scale detection to determine the matching results. Therefore, the algorithm is insensitive to scale differences. Extensive experiments demonstrate the effectiveness and accuracy of our proposed method in matching acoustic and optical images.
Highlights
In recent years, the research of underwater exploration using either acoustic imaging or optical imaging alone has made significant contributions to applications of underwater target detection, underwater archaeology, seabed resource exploration, biological research, underwater environment monitoring and other fields [1,2,3,4,5]
If the target object is in the sound shadow, it will completely change the appearance of the object in the sonar image, which will affect the matching effect
Our method is evaluated on these 10 datasets, and the matching performance of underwater images is compared with other methods
Summary
The research of underwater exploration using either acoustic imaging or optical imaging alone has made significant contributions to applications of underwater target detection, underwater archaeology, seabed resource exploration, biological research, underwater environment monitoring and other fields [1,2,3,4,5]. These two image exploration methods have their own advantages, but they have some constraints. Scattering can change the distribution of light energy in space and time, produces high levels of noise, affects the imaging signal-to-noise ratio, and can even prevent imaging when backscattering is Sensors 2020, 20, 4226; doi:10.3390/s20154226 www.mdpi.com/journal/sensors
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