Evaluation of glint correction approaches for fine-scale ocean color measurements by lightweight hyperspectral imaging spectrometers

Abstract

Low-power, lightweight, off-the-shelf imaging spectrometers, deployed on above-water fixed platforms or on low-altitude aerial drones, have significant potential for enabling fine-scale assessment of radiometrically derived water quality properties (WQPs) in oceans, lakes, and reservoirs. In such applications, it is essential that the measured water-leaving spectral radiances be corrected for surface-reflected light, i.e., glint. However, noise and spectral characteristics of these imagers, and environmental sources of fine-scale radiometric variability such as capillary waves, complicate the glint correction problem. Despite having a low signal-to-noise ratio, a representative lightweight imaging spectrometer provided accurate radiometric estimates of chlorophyll concentration—an informative WQP—from glint-corrected hyperspectral radiances in a fixed-platform application in a coastal ocean region. Optimal glint correction was provided by a spectral optimization algorithm, which outperformed both a hardware solution utilizing a polarizer and a subtractive algorithm incorporating the reflectance measured in the near infrared. In the same coastal region, this spectral optimization approach also provided the best glint correction for radiometric estimates of backscatter at 650 nm, a WQP indicative of suspended particle load.

Evaluation of Unoccupied Aircraft System (UAS) Remote Sensing Reflectance Retrievals for Water Quality Monitoring in Coastal Waters

“…However, more recent studies have shown that ⍴ can be spectrally dependent due to the degree of sky polarization and the ratio of diffuse to direct light; assuming a spectally constant ⍴ in a roughened sea surface with multi-angular wave facets can lead to erroneous estimates of L SR (Lee et al, 2010;Mobley, 2015). Lee et al (2010) proposed a spectral optimization approach using spectral inherent optical properties to model R rs, which has been applied in UAS remote sensing studies (O'Shea et al, 2020).…”

“…UAS can enhance fine-scale physical oceanography research by resolving small-scale phenomena and physical processes such as patchy algal blooms, frontal structures, and turbulence characteristics (Figure 11, Shang Z. et al, 2017;Osadchiev et al, 2020). UAS remotely sensed water quality retrievals will also likely improve with the development of lightweight, off-the-shelf hyperspectral sensors, allowing for higher spatial and spectral resolution to better distinguish optical properties of the water (Shang S. et al, 2017;O'Shea et al, 2020).…”

Using flat phosphor layer in dual-layer remote phosphor configuration to improve luminous efficacy

“…The issue was studied through intensive research and many solutions that suggest changing the configuration or particles setting for better light output were proposed. These solutions include applying phosphor with pattern or molded with particular shape [6], adding more phosphor layers into the structure [7], blending with other substances such as nanoparticles [8], and using other innovative phosphor with distinct traits [9]. Others try to achieve enhanced emitted light through LEDs alteration with the reflector [10].…”

MgCeAl11O19:Tb3+ and Mg8Ge2O11F2:Mn4+ in enhancing the color quality of remote phosphor LED

“…In addition, limiting the loss of light from backscattering and enhance the dispersal of blue and yellow lights are crucial objectives in making greater quality WLEDs. In terms of luminous efficiency, the concentration of the phosphor is as important as the structure of the package [13][14][15][16][17]. The re-absorption loss in the phosphor and the phosphor concentration are related to each other, which means if one aspect rises it will cause an increase in others.…”