Bubbles and foam appear all over the place. So why are they not a big problem? Back-scattering efficiency is the dimensionless ratio of the scattering area to the cross-sectional area of the particle. A high-efficiency scatterer reflects more light back toward an emitter than a low efficiency one. This is analogous to taking the product of absorptivity and concentration to estimate the absorption of dissolved, material (see absorption effects).

The VSF for bubbles, in the range of scattering angles from 100° to 170° lies between those for organic material and minerals. Most significantly, the VSF values are about 80% less than for minerals and this means it takes about five times more bubbles than mineral particles to produce the same intensity of light scattering, other things being equal. Bubble size and concentration are more important than efficiency because these factors can vary by more than a factor of 100 in the environment. In order to determine if bubbles interference is significant, we reviewed bubble concentration data taken under breaking waves and compared the maximum observed bubble concentrations in the silt-sand-size range with the threshold concentration of sand (10 mg l^-1) needed to produce measurable OBS signals. The maximum bubble concentration is about an order of magnitude less than threshold SSC for sand. So, when low backscatter efficiency is combined with low bubble concentration, we find that bubbles are not of concern even in foamy, aerated environments, and the visual effects of bubbles and foam are misleading.