The response of volume reflectance to manipulated algal concentrations above bright and dark bottoms at various depths in an experimental pool

We investigated changes in spectral reflectance associated with manipulations of algal densities and both bright and dark “bottoms”; at various depths in a 9500 L pool. Spectroradiometer data were collected at close range under natural sunlight. We found orderly patterns of either increasing or decreasing volume reflectance dependent on algal density, bottom color, and bottom depth. The color of the submerged bottom affected reflectance signals, especially the magnitude of the difference between the points of peak near‐infrared reflectance and chlorophyll‐dependent red absorption. Wavelength shifts in reflectance parks were detected as algal chlorophyll was reduced from 336 to 32 mg/m3. The wavelength of peak green reflectance increased from 552 to 567 nm and the near‐infrared peak from 695 to 717 nm.