Comparing the polarimetric response of hyperspectral imagers

Logan, Riley D.; Venkatesulu, Erica; Shaw, Joseph A.

doi:10.1117/12.2595588

Cited by 2 publications

(2 citation statements)

References 17 publications

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“…where L tot is the total upwelling spectral radiance, L b is the spectral radiance reflected from the benthos, L wb is the spectral radiance scattered to the imager from the water body, L ws is the spectral radiance reflected from the water's surface, L atm is the spectral radiance scattered from the atmosphere, and all terms are a function of wavelength, λ. Each term can also have variable polarization, which creates radiometric errors if the polarizationsensitive instrument response is ignored [65,66]; however, this becomes negligible for the small incidence angles (less than 8 With the exception of stormflow and snowmelt conditions, the UCFR is clear and shallow, meaning the majority of the downwelling solar irradiance will be reflected from the stream bed itself, making L b the dominant signal reaching the imager. Upwelling radiance from optical scattering within the water body prior to reaching the bottom substrate, L wb , largely depends on the water's inherent optical properties.…”

Section: Theoretical Basis For Isolating Stream Bed Reflectancementioning

confidence: 99%

UAV-Based Hyperspectral Imaging for River Algae Pigment Estimation

et al. 2023

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Harmful and nuisance algal blooms are becoming a greater concern to public health, riverine ecosystems, and recreational uses of inland waterways. Algal bloom proliferation has increased in the Upper Clark Fork River due to a combination of warming water temperatures, naturally high phosphorus levels, and an influx of nitrogen from various sources. To improve understanding of bloom dynamics and how they affect water quality, often measured as algal biomass measured through pigment standing crops, a UAV-based hyperspectral imaging system was deployed to monitor several locations along the Upper Clark Fork River in western Montana. Image data were collected across the spectral range of 400–1000 nm with 2.1 nm spectral resolution during two field sampling campaigns in 2021. Included are methods to estimate chl a and phycocyanin standing crops using regression analysis of salient wavelength bands, before and after separating the pigments according to their growth form. Estimates of chl a and phycocyanin standing crops generated through a linear regression analysis are compared to in situ data, resulting in a maximum R2 of 0.96 for estimating fila/epip chl-a and 0.94 when estimating epiphytic phycocyanin. Estimates of pigment standing crops from total abundance, epiphytic, and the sum of filamentous and epiphytic sources are also included, resulting in a promising method for remotely estimating algal standing crops. This method addresses the shortcomings of current monitoring techniques, which are limited in spatial and temporal scale, by proposing a method for rapid collection of high-spatial-resolution pigment abundance estimates.

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Section: Theoretical Basis For Isolating Stream Bed Reflectancementioning

confidence: 99%

UAV-Based Hyperspectral Imaging for River Algae Pigment Estimation

et al. 2023

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“…6,7 The surface reflections can reduce the signal measured or cause errors due to the polarization response of the imagers. 8 Developing a quantitative understanding of the contrast enhancement from using a polarizer through the controlled experiments in this work will help inform how well the addition of a polarizer to these imagers could mitigate these effects.…”

Section: Introductionmentioning

confidence: 99%

Contrast enhancement through an air-water interface with polarization imaging

Venkatesulu,

Buglione,

Field

et al. 2023

Polarization Science and Remote Sensing XI

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It is well known that underwater objects become more readily visible when viewed through a vertical polarizer that suppresses horizontally polarized reflections from the air-water interface. However, quantitative measurements of the contrast enhancement achieved with a polarizer do not seem to have been reported in the literature. To measure the polarization-enabled contrast enhancement, we placed white and black tiles next to each other, immersed in water, then measured the optical contrast between them as a function of viewing angle (relative to the surface normal) with a polarization camera that simultaneously recorded images with linear polarization oriented 0°, 90°, and 45°from horizontal. Images were recorded with an RGB polarization camera through approximately 45 cm of water at Bozeman Pond and with a monochrome polarization camera through approximately 5 cm of water at Bozeman Beach. Images also were recorded with the monochrome camera and a filter to isolate the near infrared band of approximately 750 to 1000 nm. Indoor laboratory measurements also were recorded to verify the role of the color of the reflecting background. All experiments used carefully calibrated division-of-focal-plane polarization cameras. The observed contrast decreased with viewing angle, but less so for the vertically polarized images. The contrast enhancement, represented by the ratio of vertically polarized to unpolarized contrast, increased with viewing angle, even past the Brewster angle (approx. 53°). The contrast enhancement only began decreasing for viewing angles larger than 70°. In outdoor experiments with a mostly clear sky, the highest contrast enhancement was in the blue spectral band. The contrast was essentially the same for red, green, and blue bands with a white background. In all measurements, the black tile exhibited much larger degree of linear polarization, which is an example of the Umov effect. In this paper we describe the experiments, show and explain polarization images, and show and explain plots of contrast and contrast enhancement as a function of viewing angle.

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Comparing the polarimetric response of hyperspectral imagers

Cited by 2 publications

References 17 publications

UAV-Based Hyperspectral Imaging for River Algae Pigment Estimation

UAV-Based Hyperspectral Imaging for River Algae Pigment Estimation

Contrast enhancement through an air-water interface with polarization imaging

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