The Discovery Programme collaborated with UCD School of Archaeology on a Heritage Council funded project to conduct advanced studies on the remains of wooden fishweirs exposed on mudflats of the Fergus Estuary near Boarland Rock. A part of the project aimed to assess the value in recording such complex and fragile remains at high resolution in 3D, generating data sets which could then be examined and studied in greater detail off-site. The wooden remains, situated on thick mudflats in the middle of the estuary, are only exposed during periods of extreme low tides and even then for a maximum of only 3 hours a day. Access to the sites had to be carefully planned, hiring small flat-bottomed boats and local boatmen with the detailed knowledge and experience of the tides and currents to land us and our equipment safely on site.

The aim was to concentrate the laser scanning on three of the best preserved fishweirs while simultaneously conducting a DGPS survey of the other remains, simply recording a point on each upright post. By the end of the four field days the intention was to have a plan overview of the currently exposed timber remains, with high resolution 3D data from our laser scanning for three examples.

The laser scanner used on the project was a Mensi GS101 time of flight scanner. The instrument was powered by a Kippor Sinemaster 1000 petrol generator and controlled by Trimble PointScape 3.2 hosted on a ruggedized Panasonic Toughbook CF19. Processing was done using Trimble Realworks 6.5.

DGPS for both georeferencing the laser scans and surveying the wider area fragments was done using a pair of roving Trimble 5800 receivers with a local base station provided by UCD, again a Trimble 5800. Due to the hostile environment (mudflats submerged by the incoming tide) a new base station had to be established each day, its position fixed in Irish Grid coordinates using the Trimble VRS NOW correction service via a GSM mobile phone link.

The primary result of the survey is a georeferenced pointcloud dataset, segmented into the three structures recorded. Beyond the pointcloud data a range of GIS compatible outputs including plan view orthoimages and derived shapefiles were also generated to be incorporated into the wider area DGPS survey. These GIS products will provide a useful framework for the further scientific analysis taken place on the fishweirs e.g. wood species and date analysis. Some experimental 3D reconstruction with extruded posts based on heights measured from the pointcloud has been undertaken.

 A pdf version of the survey report for this project is available to download, see below.

 Fergus Estuary Survey Report (1.3 MB 2010-11-26 12:57:11