Sunlight induced chlorophyll fluorescence in the near‐infrared spectral region in natural waters: Interpretation of the narrow reflectance peak around 761 nm

Abstract

Sunlight induced chlorophyll a fluorescence (SICF) can be used as a probe to estimate chlorophyll a concentrations (Chl) and infer phytoplankton physiology. SICF at ∼685 nm has been widely applied to studies of natural waters. SICF around 740 nm has been demonstrated to cause a narrow reflectance peak at ∼761 nm in the reflectance spectra of terrestrial vegetation. This narrow peak has also been observed in the reflectance spectra of natural waters, but its mechanism and applications have not yet been investigated and it has often been treated as measurement artifacts. In this study, we aimed to interpret this reflectance peak at ∼761 nm and discuss its potential applications for remote monitoring of natural waters. A derivative analysis of the spectral reflectance suggests that the 761 nm peak is due to SICF. It was also found that the fluorescence line height (FLH) at 761 nm significantly and linearly correlates with Chl. FLH(761 nm) showed a tighter relationship with Chl than the relationship between FLH(∼685 nm) and Chl mainly due to weaker perturbations by nonalgal materials around 761 nm. While it is not conclusive, a combination of FLH(761 nm) and FLH(∼685 nm) might have some potentials to discriminate cyanobacteria from other phytoplankton due to their different fluorescence responses at the two wavelengths. It was further found that reflectance spectra with a 5 nm spectral resolution are adequate to capture the spectral SICF feature at ∼761 nm. These preliminary results suggest that FLH(761 nm) need to be explored more for future applications in optically complex coastal and inland waters.

Potential for High Fidelity Global Mapping of Common Inland Water Quality Products at High Spatial and Temporal Resolutions Based on a Synthetic Data and Machine Learning Approach

“…A second oversimplification pertains to the shape of the modeled Gaussian fluorescence emission. In reality, while chl-a fluorescence does indeed have a major fluorescence emission around 685 nm, it also has an adjacent vibrational satellite emission centered around 730-740 nm (Govindjee, 2004 and references therein;Lu et al, 2016). Although generally smaller in amplitude due to increased absorption from water farther into the near-infrared (NIR), this 730-740 nm fluorescence emission can potentially contribute to the water leaving radiance.…”

Sensitivity Analysis and Optimization of a Radiative Transfer Numerical Model for Turbid Lake Water

“…Chl-a fluorescence quantum efficiency was the 11th (of 12) parameter in terms of sensitivity. This parameter affected specific Chl-a absorption and also improved the fit of the Chl-a reflectance estimates with the near-infrared spectral peaks [59,60]. However, the fluorescence quantum efficiency has been considered less variable than is commonly believed [61].…”

Comparing the Use of Red-Edge and Near-Infrared Wavelength Ranges for Detecting Submerged Kelp Canopy

“…Typically, the R 0+ within the NIR wavelength range overwhelms the signal from SICF, however, atmospheric gasses highly absorb incoming irradiance at 761 nm, which can create a fill-in effect by the SICF in this region [53]. While this phenomenon has been correlated with photosynthetic output and general health of terrestrial vegetation and phytoplankton [53,54], we are not aware of any publications that report an SICF peak in kelp spectra, and this may present an opportunity for future hyperspectral research. Once kelp was submerged the SICF feature was dampened, and therefore future research should take note of the amount of kelp at the surface if attempting to derive information from an SICF peak.…”