• Minimise the demand for primary aggregates.
• Promote environmentally friendly extraction and transport.
• Reduce the effect of local aggregate extraction.

Siddhi Joshi

MSc Hydrographic Surveying
UCL

Research into the Use of Multibeam Backscatter for Seabed Classification in the Outer Thames Estuary

Abstract

Multibeam systems collect both bathymetry and backscatter data and can be used for seabed classification. Two different approaches to seabed classification, the image-based method and the angular response characterisation approach have been studied andsubsequently compared. Seabed classification methods are one way of characterising theseabed and have many applications in the field of seabed mapping. This study has used the Quester Tangent Corporation (QTC) image-based method and the newer Geocodersoftware's angular response characterisation approach to characterise two areas affected by dredging activities. The QTC approach divides the region into discrete classes, which are subsequently identified by groundtruthing. Geocoder is able to make remote estimates of the physical properties of the seafloor using the Angular Range Analysis (ARA) method.

First, the North Edinburgh Channel sand placement site, monitored by the Port of London Authority, is studied. Results include different types of multibeam backscatter mosaics, partially stacked backscatter, angular response curves and remote estimates of the grain size. Overall, Geocoder results here show good agreement with groundtruthing. The QTC unsupervised classification approach is used to identify and monitor the classes in the area of relocation. This effectively distinguishes between the coarser relocated material and classes in the North Edinburgh Channel seabed.

Geocoder ARA results from the second site; the Thames Regional Environmental Characterisation survey area, has been studied and compared with the QTC classification. Results suggest that the QTC method can more effectively discriminate between areas affected by aggregate extraction in this region. The Geocoder software however shows great potential, allowing quantitative information about the grain size, acoustic impedance and seafloor roughness to be determined using multibeam data. Both approaches have their merits and can be used as part of seabed characterisation studies in a wide range of applications.