Innovative Techniques for Improved Hydroacoustic Bottom Tracking in Dense Aquatic Vegetation

摘要

Detection of the true depth of the bottom beneath dense submersed aquatic vegetation is problematic using conventional hydroacoustic bottom tracking approaches. This may lead to underestimation of bottom depth, erroneous bathymetric maps, and overestimates of dredging quantities. A hydrographic data set was collected in Wood Island Harbor (a U.S. Army Corps of Engineers small boat harbor on the Maine coast, which contains heavy growth of Zostera marina (eelgrass)) to compare two single-beam transducer systems. One used conventional signal processing for bottom tracking, while the other employed an innovative alternative approach designed specifically for detecting submersed vegetation. Bottom tracking results between systems agreed well in unvegetated areas, but the conventional system increasingly underestimated bottom depth as vegetation density and height increased. This was attributed to failure to consider the high acoustical reflectivity of the vegetation canopy in digital signal processing. Alternative data processing approaches, using the captured raw digital signal, were evaluated to determine some easily implemented signal processing techniques to alleviate the problem. Several potentially feasible signal processing approaches, which could be used with existing hydrographic hardware, are identified and described.