Comparison of forward modeling of apparent hydrooptical properties with in situ observations of multi-spectral data in Saginaw Bay: water quality retrievals and implications for SeaWiFS data processing

Abstract

Some field measurements of the downwelling solar irradiance above the water surface and the upwelling subsurface solar radiance as well as in situ determinations of phytoplanktonic chlorophyll, total suspended sediments and dissolved organic matter concentrations were performed in Saginaw Bay, Lake Huron, during July and August 1998. The radiometric experiments were carried out at the wavelengths specific for SeaWiFS (412, 443, 490, 510, 555, 665 nm) and accompanied by the observations of weather conditions (wind force and direction, wave height, cloudiness nature and degree) and the Sun elevation. The task of the present study was to solve the forward and inverse problems: to calculate the upwelling radiance using hydrooptical model and the analytical expression for the volume reflectance coefficient, to compare it with in situ data and to retrieve the concentrations of the optically active components (OAC). In the absence of the hydrooptical model for Saginaw Bay forward modeling was conducted using hydrooptical models of other temperate lakes. The retrievals of chlorophyll, suspended minerals (SM) and dissolved organic carbon (DOC) were calculated with the help of the multivariate optimization technique (MOT) and neural network approach.