Underwater Optical Imaging: Key Technologies and Applications Review

Abstract

The challenges associated with acquiring the clear images of objects in underwater environment are difficult to overcome due to the absorptive and scattering nature of seawater. Recently, the research community has focused on mitigating these effects. The recent developments in image enhancement algorithms and strategies of signal light enhancement have brought improvement in some application areas. In this work, we review the six most common methods based on signal light enhancement. We present the individual working mechanisms, latest representative advances, and suitable application conditions. Moreover, we also present a detailed comparison of these techniques. In each technique, we present their applicable environments and conditions according to the following indicators: operating distance (from 2 attenuation lengths (AL) to 13.5 AL), resolution (from centimeter to millimeter), and field of view (FOV). By summarizing and analyzing the existing problems that restrict the underwater optical imaging techniques, the future development trends are prospected. INDEX TERMSUnderwater optical imaging, Underwater imaging model, Signal light enhancement, Optical properties of seawater

Autonomous Underwater Vehicles: Identifying Critical Issues and Future Perspectives in Image Acquisition

“…However, actual underwater image databases also suffer from qualitative issues, as most of them only provide near-field targets that must be recognized. While foreground targets can be acquired and detected with greater success and simpler enhancement techniques, such as contrast stretching, future image datasets should provide enhanced quantitative and qualitative data by adding the spatial distance variable [ 19 ] so that issue-related character and far-field detection could be better addressed.…”

“…Despite the fact that underwater sensing reviews are currently scarce, some of them are centered on obtaining a general overview of the topic, usually focused on the categorization of optical images [ 9 , 10 ]. Thus, future and critical issues are not usually detected; the most favorable cases of those that were studied briefly mention some general issues in the conclusion that are to be left for future work [ 19 ]. On the contrary, the aim of this work is to provide a comprehensive, step-by-step, critical issue analysis and future prospects regarding the entire underwater vision process, considering the present technological and algorithmic state-of-the-art in which we are involved.…”

Microimage coupled Raman optical probes for benthic solid target detection

“…Unlike the laboratory environment, the scattering and absorption properties of seawater cause image degradation, and nonuniform illumination can also incorrectly display the highlights and hidden information in dark areas, influencing the accuracy of underwater imaging and posing challenges for the later image process. [ 18–20 ]…”

“…Unlike the laboratory environment, the scattering and absorption properties of seawater cause image degradation, and nonuniform illumination can also incorrectly display the highlights and hidden information in dark areas, influencing the accuracy of underwater imaging and posing challenges for the later image process. [18][19][20] In the MICRO system, a unique immersed illuminator is designed to provide low scattering and uniform illumination for the imaging area. In this component, 16 high-power LED beads (epoxy encapsulated, 0.5 W, 55-60 lm, 8-10 irradiation angle, 6000-6500 k) were symmetrically embedded in a 3D printed circular plastic base with an angle of 68.2 to the system centre axis.…”

Cleaning up the world’s oceans with underwater laser imaging

“…In this case, the power of the laser would determine the maximum distance between the object and underwater vehicle at which images could be obtained. However, different factors may affect the quality of underwater images (29).…”