Remote measurement of algal chlorophyll in surface waters: The case for the first derivative of reflectance near 690 nm

Remote sensing is an important technology for measuring algal-chlorophyll concentrations in surface waters. Our paper provides hyperspectral signatures, in the visible and near-infrared, associated with two experiments conducted outdoors in large water tanks; one involving relatively low amounts of chlorophyll over a narrow range and a second involving relatively high amounts over a wide range. The principal finding was that the commonly used near-infrared/red ratio is best for estimating pigment amounts when the concentration of chlorophyll is relatively low, and the first derivative of reflectance around 690 nm is best when the concentration is relatively high.