Frank O. Nitsche

Lamont-Doherty Earth Observatory
of Columbia University
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Process related classification of acoustic data from the Hudson River Estuary

Frank O. Nitsche, Robin Bell, Suzanne M. Carbotte, William B.F. Ryan, and Roger Flood


Acoustic surveying provides valuable information on the distribution of sedimentary environments in subaqueous settings. Frequently, differences in acoustic backscatter strength are used to distinguish sedimentary environments on the basis of their grain size composition. Here, we are presenting acoustic backscatter data from the Haverstraw Bay section of the Hudson River Estuary that are better explained by sedimentary processes than by a variable such as sediment grain size distribution.

The entire 240 kilometers of the Hudson River Estuary has been mapped using sidescan, chirp sub-bottom profiling, and multibeam bathymetry as part of the Benthic Mapping Project of the Hudson River Estuary Program, funded by New York State. In additon, hundreds of gravity cores, and grab samples provide ground truth for a classification of the river bottom into discrete substrate types. Analyses of sedimentary environments reveal patterns in backscatter strength beyond those that can be related to the sediment grain size distribution alone. An integrated interpretation of sidescan, sub-bottom profiling, and high-resolution bathymetry data indicates that the backscatter pattern can be attributed to spatial variations in the modern depositional environments which cause differences in bottom roughness and sediment compaction. Based on an integrated interpretation of the acoustic and sample data sets we distinguished eight different sedimentary classes. Many of the classes can be linked to dynamic processes including contemporary deposition, winnowing, erosion, and sediment migration in sand waves. The results provide a better understanding of the dynamic processes of the Hudson River Estuary and improve the interpretation of the acoustic backscatter data from fine grained sedimentary environments.

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Frank Nitsche - last update 9/27/2005