Pixelwise immersion factor calibration for underwater hyperspectral imaging instruments.

In situ spectral reflectance initially captured at high spatial resolution with underwater hyperspectral imaging (UHI) is effective for classification and quantification in oceanic biogeochemical studies; however, the measured spectral radiance is rarely used as an absolute quantity due to challenges in calibration of UHI instruments. In this paper, a commercial UHI instrument was calibrated for radiometric flat field response and pixelwise immersion effect to support in situ measurement of absolute spectral radiance. The radiometric and immersion factor calibrations of the UHI instrument were evaluated quantitatively through comparative experiments with a spectroradiometer and a spectrometer.

Photophysiologically active green, red, and brown macroalgae living in the Arctic Polar Night.

Arctic macroalgae species have developed different growth strategies to survive extreme seasonal changes in irradiance in polar regions. We compared photophysiological parameters such as the light saturation parameter (E) and pigment composition of green, red, and brown macroalgae collected in January (Polar Night) and October 2020 (end of the light season). Macroalgae in January appeared healthier (morphologically) and had longer lamina (new growth) than those in October.