Underwater Spectral Imaging System Based on Liquid Crystal Tunable Filter

Abstract

In the past decade, underwater spectral imaging (USI) has shown great potential in underwater exploration for its high spectral and spatial resolution. This proposal presents a stare-type USI system combined with the liquid crystal tunable filter (LCTF) spectral splitting device. Considering the working features of LCTF and the theoretical model of USI, the core structure containing “imaging lens-LCTF-imaging sensor” is designed and developed. The system is compact, and the optical geometry is constructed minimally. The spectral calibration test analysis proved that the spectral response range of the system covers a full band of 400 nm to 700 nm with the highest spectral resolution between 6.7 nm and 18.5 nm. The experiments show that the system can quickly collect high-quality spectral image data by switching between different spectral bands arbitrarily. The designed prototype provides a feasible and reliable spectral imaging solution for in situ underwater targets observation with high spectrum collecting efficiency.

Investigating the rate of turbidity impact on underwater spectral reflectance detection

“…Later, the underwater spectral imaging system is sealed for waterproofing followed by the optical system installation and underwater pressure test analysis. To ensure the accuracy and reliability of the spectral imaging system, imaging parameters such as spectral resolution, spectral response sensitivity, and underwater detection sensitivity are tested and calibrated with a standard monochromator and spectrometer (Song et al 2021a).…”

“…A liquid crystal tunable filter (LCTF) can switch its central wavelength through electrical signal control without moving mechanical structure, simplify the system structure, and improve reliability, response speed, and automation. Based on a stare-type underwater spectral imager based on LCTF (Song et al, 2021a), this paper explores the influence of different water turbidity and lighting conditions on the accuracy of spectral reflectance detection methods.…”

“…FIGURE 1Encapsulated structure of the designed USI system. The hardware includes optical (lens, LCTF, and imaging sensor) and control (microcomputer, motor drive circuit, remote I/O circuitry, and voltage converter) modules installed in a waterproof mechanical structure(Song et al 2021a). …”

Underwater hyperspectral imaging bioinspired by chromatic blur vision

“…However, its optical system has an unrectified axial chromatic aberration, with a focal length offset of about 0.75 mm in the visible band range of 400 nm-700 nm. Based on the previous studies [17,20], Stubbs and Stubbs [24] further found that the epiretinal imaging has a large vertical axis chromatic aberration, namely blur defocused images, due to the high axial chromatic deviation of the eyeball optical system and the large aperture or off-axis pupil characteristics. Thus, they believed that squids may adjust the accommodation between the eyeball and the retina to obtain a series of chromatic blur images at the axial position on the retina, and approximately perceive various reflected spectral components of the target object through the image contrast analysis of each frame.…”

“…Moreover, these scanning devices and platforms complicate the overall mechanical structure required in imaging. In addition, there exist other spectral imaging techniques that can be implemented by setting up a tunable light source [16] or using a liquid crystal tunable filter (LCTF) [17].…”