Geological Processes

Suspended Matter Concentrations &mdash Sediments & Turbidity

Suspended matter concentrations and patterns change very rapidly as tides, winds, and river discharge fluctuate. This strong variability complicates interpretation of remotely sensed information regarding estuarine circulation, transport and distribution of river discharge, and mixing processes. The frequent sampling required, however, to resolve tidal effects cannot be provided by data from polar-orbiting spacecraft. These data must be supplemented with more frequent acquisitions from aircraft, buoys, drifters, and ships. Satellite sensors can, however, provide global access to remote areas where coastal processes can be imaged synoptically.

Sediment load in the water greatly regulates the primary production of seagrasses and phytoplankton by strongly affecting light availability within the water column. Estimates of the diffuse attenuation coefficient K and its correlation to the reflectance of the water allow some prediction to be made of the light field within a sediment-loaded environment. Suspended sediments may also act as "tracers" (streak lines) that reveal circulation patterns in areas where sea-surface temperature and/or chlorophyll pigment concentration may not be readily apparent or recoverable.

The turbidity of the water controls the total reflectance leaving the water. Thus, river discharge generally high in terrigenous material and degradation products from primary productivity may be observed with sensors possessing a high saturation radiance such as the AVHRR. Due to the high frequency sampling of the AVHRR, detailed pictures of the time evolution of plumes in the Mississippi Delta and Mobile Bay (March 24, March 25, March 26, March 27). Stumpf and Tyler (1988) have constructed a model that estimates seston concentration from the received radiances, assuming the absorption and scattering characteristics of the suspended particles are known. These properties are specific to a region and time of year; thus, the application of such a model needs to be carefully performed. One such survey has been performed for a spring Mobile Bay plume (Apr 3, pm; Apr 4, am; Apr 4, pm; Apr 5, am; and Apr 5, pm). In such imagery, the rapid changes in sediment load in the water is apparent. Further information may be obtained in Stumpf and Pennock (1991).

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