A towed near-surface optical reflectance meter for measuring ocean colour in support of remote sensing

An underwater optical instrument, the Lighfish, measures near-surface irradiance reflectance in six spectral channels while it is towed from a research vessel at a depth of a few metres. The detectors are configured such that all downward-looking detectors observe the same instrument shadow. Effects of self-shading are negligible for waters and wavelengths having absorption coefficients less than 0.3 m−1. Variance in the derived spectral reflectance ratios is shown to be significantly reduced compared with that in single channel irradiance measurements. The instrument can be used to develop remote sensing algorithms as well as for other oceanographic applications.