The backscattering coefficient and its components in the Great Lakes: A review and synthesis

Abstract

Backscattering of light by particulates, as quantified by the particulate backscattering coefficient, bbp (m–1), is important in regulating the optical signal available for remote sensing. A synthesis of the available information on bbp for the Laurentian Great Lakes is presented to support mechanistic approaches for remote sensing. This includes (1) direct measurements of bbp, (2) characterization of the backscattering attributes of minerogenic particles, (3) partitioning of bbp into contributing minerogenic (bb,m) and organic (bb,o) components, and (4) development of appropriate cross-sections (mass-specific coefficients) for retrieval of concentrations of backscattering constituents by remote sensing. Levels of bbp were particularly high in the western basin of Lake Erie and Green Bay, Lake Michigan, intermediate levels prevailed in parts of Lake Ontario during a whiting event, and values were substantially lower in the open waters of the upper Great Lakes. Minerogenic backscattering (bb,m) is an important component of bbp throughout the system. Clay mineral particles dominate this component, except during whiting events when calcite is dominant. Mie-theory calculations supported estimates of bb,m, and together with particle morphological considerations, guided the development of the optical cross-section for minerogenic particles. The collected data and associated analyses are appropriate to support initiatives to develop and preliminarily test mechanistic remote sensing approaches for the Great Lakes.