Backscattering by Particles of Sizes <0.2 μm in Seawater

We measured the angular scattering functions at 517 nm in different size fractions, including bulk and very small particles (VSP for diameters <0.2 μm), in a variety of waters ranging from coasts to open oceans and from surface to depths as deep as 3,000 m. The measurements revealed a strong covariation in backscattering between VSP and bulk particle populations. The fractional contribution by VSP decreases from 60% in clear oceanic water where bulk particle backscattering coefficient b bp is on the order of 0.001 m −1 to <2% in turbid coastal water where b bp ∼0.1 m −1 . An empirical model is developed ( r 2 = 0.89) to estimate b bp for VSP from the bulk b bp , which can now be routinely obtained from satellite observations.