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software then allows an interpretation to be applied to the data by identifying and selecting a sedimentary boundary that might be of archaeological interest.


25.


The sub-bottom profiler data were interpreted with a two-way travel time (TWTT) along the z-axis. In order to convert from TWTT to depth, the velocity of the seismic waves was estimated to be 1,600ms-1. This is a standard estimate for shallow, unconsolidated sediments.


26. Any small reflectors which appear to be buried material such as a wreck site covered by sediment were also recorded, the position and dimensions of any such objects noted in a gazetteer, and an image of each anomaly acquired. It should be noted that anomalies of this type are rare, as the sensors must pass directly over such an object in order to produce an anomaly.


1.1.4 Geophysical Data – Anomaly Grouping and Discrimination 27.


The previous section describes the initial interpretation of all available geophysical data sets which were conducted independently of each other. This inevitably leads to the possibility of any one object being the cause of numerous anomalies in different data sets and apparently overstating the number of archaeological features in the study area.


28.


To address this fact the anomalies were grouped together along with the results of the desk-based study of known archaeological sites. This allows one ID number to be assigned to a single object for which there may be, for example, a UKHO record, a magnetic anomaly and multiple sidescan sonar anomalies.


29.


For seabed anomalies previously identified within the Study Area, the unique ID number has been retained from the 2012 ZEA assessment (Appendix 17.3) and is discussed in this report. Also, previously identified anomalies have been re-assessed based on the recent dataset.


30.


For the palaeogeographic interpretation, only previously identified features that coincide with features identified using the more recent, higher resolution data have been included within the results. Any such features are recorded in Appendix 17.3.


31. Once all the geophysical anomalies and desk-based information have been grouped, a discrimination flag is added to the record in order to discriminate against those which are not thought to be of an archaeological concern. For anomalies located on the seabed, these flags are ascribed as follows:


Table 1.2.Criteria Discriminating Relevance of Seabed Features to Proposed Scheme Non-Archaeological U1


Not of anthropogenic origin U2 Preliminary Environmental Information May 2014


Known non-archaeological feature East Anglia THREE Offshore Windfarm


Appendix 17.2 Archaeological Review of


Geophysical and Geotechnical Data: Technical Report


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