Simple multi-filter sensors for determining relative radiation in the sea and in freshwater

The design, construction, testing and use of an underwater relative radiation sensor are described. The sensor incorporates four narrow band interference filters and a broad band (400–700 nm) filter so that variation in spectral quality as well as visible light attenuation can be determined. Comparison with a proprietary, calibrated sensor, a Macam SD 101, indicates the reliability of the relative radiation sensor of the range 1 to >300 Wm^–2 P.A.R. and to a depth of at least 20 m. Brief reference is made to selected data from a variety of aquatic habitats. A general table for the comparison of radiation and illumination units is presented.