Variation in the projected surface area of suspended particles: Implications for remote sensing assessment of TSM

For decades, researchers have attempted to develop general algorithms for determining the concentration of total suspended matter (TSM) in coastal waters using remotely sensed measurements. On the basis of published work and empirical data, this paper demonstrates that reflectance and other optical parameters, such as the beam attenuation coefficient, are in reality, dependent on the projected surface area (PSA) of the suspended matter. The PSA is shown to be dependent on TSM, the volume concentration (VC), the particle size spectrum, and the mean effective density (Δρ) of the suspended matter. The PSA is calculated for three different particle size spectra and it is shown that PSA can vary by up to three orders of magnitude at a constant value of TSM (if Δρ and the particle size spectrum change). Because reflectance and beam attenuation are de facto related to the PSA, determination of TSM from a reflectance or transmission measurement may potentially have an error of up to a factor of 10 due to variations in Δρ common in coastal and estuarine waters. If Δρ and the size spectrum of the suspended matter are known or can be estimated, it is possible to determine TSM from both types of measurement with better accuracy.