A day on water and a day in the lab
One of the downfalls of marine geophysical surveying is, to a degree, its cost. Although it is becoming much more affordable, sometimes given the lack of archaeological funding we are obliged to find alternative ways, but equally sufficient for our needs. I was fortunate to attend training at the University of Ulster recently, funded by the Honor Frost Foundation, on one of their Lowrance Structure Scan system, in order to be able to use the system and apply it in a fieldwork elsewhere this summer. The StructureScan is an easy to use system consisting of a transmitter, display unit, and a side scan sonar with an in-built single beam echo sounder. Dr Kieran Westley suggested the use of this system for archaeological purposes particularly in shallow waters. The StructureScan is commonly used amongst fishermen, however its side scan unit has also the potential to be used for archaeological investigations of the seabed. It works well for shallow water surveying, up to 20m. Given its user-friendliness, affordable price, and adequate results, this system becomes a valuable tool in the hands of archaeologists.
The training at Ulster University was for three days. One day of familiarising with the equipment and the survey area, a day of surveying, and a day of data processing. We were quite lucky with good weather, surprisingly for Ireland. Kieran had chosen the survey area for the training at Lough Beg, Northern Ireland, where a log boat is supposedly located in the vicinity of a crannog in the lake. We surveyed around the crannog following or trying to follow pre-determined survey lines in as much as the wind, current, and depth of the lake allowed. Since the purpose of the survey was to collect side scan sonar data, it was necessary to reduce the noise from the motor. We ended up surveying on a speed of 2-3 knots, realising that the data we were collecting was not the best, but it was good enough for the training exercise. The shallow parts of the lake were quite difficult to survey. We did get to see many posts showing up on the display unit and lots of vegetation which was also getting stuck to the motor’s propeller.
The survey was followed by a day of data processing using ReefMaster and SonarTRX. The former software allows to quickly review the data, locate anomalies, and generate a bathymetric map. The SonarTRX on the other hand is used to process the data by editing the lines of surveys one by one in order to get the best results from the collected data. It then permits to ge
nerate a mosaic from the survey lines which can be imported into GIS (Geographic Information Systems). Working through the software took almost a whole day, familiarising with the tools, editing, and exporting capabilities. We tend to assume that once the data is collected, the hard part is over, but in fact processing the data is much more demanding, it is a science and an art (quoting both Kieran Westley and Rorey Quinn). The nice mosaics and images we see often in marine geophysics are the result of long hours of computational work by dedicated individuals.
Finally, this training was concluded with a visit to the Giant’s Causeway, a walk along the incredible Irish coastline, a visit to a local pub, and good times with good people, all thanks to the Centre for Maritime Archaeology at the University of Ulster, particularly Dr Kieran Westley and Dr Colin Breen, and to the Honor Frost Foundation for their support.