Developing a low-cost multispectral imager for detecting algal blooms in rivers

A low-cost multispectral imager is described for routine monitoring of Cladophora nuisance algae and blue-green algae in narrow rivers that are not spatially resolved by satellites. The goal is to identify algal blooms and estimate the chlorophyll a (chl a) and phycocyanin content from a network of low-cost imagers that can be mounted on bridges, trees, or other convenient objects at key river locations. The preliminary design uses Raspberry Pi cameras and computers with bandpass filters at 568, 671, 700, and 825 nm, based on data gathered with an airborne hyperspectral imager on the Upper Clark Fork River in southwestern Montana USA. This paper summarizes the initial design, calibration measurements, and preliminary reflectance data.