The Mersey Estuary : sediment geochemistry

This report describes a study of the geochemistry of the Mersey estuary carried out between April 2000 and December 2002. The study was the first in a new programme of surveys of the geochemistry of major British estuaries aimed at enhancing our knowledge and understanding of the distribution of contaminants in estuarine sediments. The report first summarises the physical setting, historical development, geology, hydrography and bathymetry of the Mersey estuary and its catchment. Details of the sampling and analytical programmes are then given followed by a discussion of the sedimentology and geochemistry. The chemistry of the water column and suspended particulate matter have not been studied, the chief concern being with the geochemistry of the surface and near-surface sediments of the Mersey estuary and an examination of their likely sources and present state of contamination

A Hovercraft-Borne LiDAR and a Comprehensive Filtering Method for the Topographic Survey of Mudflats

To obtain the mudflat topography when existing measuring systems and data processing methods are impracticable under special conditions, this paper presents a hovercraft-borne LiDAR (light detection and ranging) system and a novel comprehensive filtering method. The system is based on a hovercraft and equipped with a laser scanner and a POS (position and orientation system). The filtering method firstly segments the point cloud into different segments by combining the geometric and intensity information, then fitting the ground surface by cloth simulation method, and finally synthetically extracts the ground points with three constraints. These constraints are the distance of the point to the fitting surface, the normal difference between the point and the fitting surface, and the proportion of the possible ground points in the total points of each segment. The effectiveness of the measurement system and the development of the post-processing results were verified on the basis of field measurements, in which a total filtering error of 0.3% and the elevation accuracy of 6.4 cm were obtained. The proposed system and methods provide a new way for efficient and accurate topographic survey on mudflats