Abstract
Underwater detection has always been a challenge due to the limitations caused by scattering and absorption in the underwater environment. Because of their great penetration abilities, lasers have become the most suitable technology for underwater detection. In all underwater laser applications, the reflected laser pulse which contains the key information for most of the system is highly degraded along the laser’s propagation path and during reflection. This has a direct impact on the system’s performance, especially for single-pixel imaging (SPI) which is very dependent on light-intensity information. Due to the complications in the underwater environment, it is necessary to study the influential factors and their impacts on underwater SPI. In this study, we investigated the influence of the angle of incidence, target distance, and medium attenuation. A systematic investigation of the influential factors on the reflectance and ranging accuracy was performed theoretically and experimentally. The theoretical analysis was demonstrated based on the bidirectional reflection distribution function (BRDF) and laser detection and ranging (LADAR) model. Moreover, 2D single-pixel imaging (SPI) systems were setup for experimental investigation. The experimental results agree well with the theoretical results, which show the system’s dependency on the reflection intensity caused by the angle of incidence, target distance, and medium attenuation. The findings should be a reference for works looking to improve the performance of an underwater SPI system.
Highlights
Over the past decade, various investigations have aimed to detect or image an object in an underwater environment [1,2,3,4,5]
Based on the above definition of single-pixel imaging (SPI) and its image reconstruction characteristics, it can be clearly observed that the reconstruction imaging quality of a SPI system is closely related to the intensity of light reflected from an object
Where PT, PR (Ym ), and R are the emitted energy, received energy, and range across, respectively; Ym is the mth measurement value; θR is the field of view of the receiver; θT is the divergence angle of the laser beam; ρT corresponds to the target reflectivity; θt is the angle of incidence of the laser beam relative to the macroscopic surface normal direction; AR is the area of the aperture of the receiver; ηT, ηR, and ηA, are the loss factors due to beam shaping unit inefficiency, receive system inefficiency, and one-way water attenuation caused by scattering and absorption, respectively
Summary
Various investigations have aimed to detect or image an object in an underwater environment [1,2,3,4,5]. Lasers have been employed in various fields, such as reverse engineering, machine vision, 3D imaging, and especially, underwater object detection [6,7,8,9]. In order to reduce effect of noise from back scattering light, we proposed a simple and stable, pulsed SPI system, and employed peak detection to conduct an experimental study. An underwater, active-mode SPI was built to determine the reflection ratio and intensity error
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