A kind correspondent, David Blocker, has looked at the Lidar images that I posted, of the ruins of “Walton Castle”, the Saxon Shore Roman fort lying submerged near Felixstowe in Suffolk, and annotated them. The results are fascinating:
Then with annotation:
As a reminder, the rough sketch map drawn by the diver Jeff Errington:
He adds:
The lidar image of the Felixstowe area reveals the ruins of the Roman fort.
The lidar image roughly corresponds to the sketch made by the scuba club in the 1970’s. There appears to be a shallow underwater channel between the beach and the offshore mound with the ruins, the groynes do not appear to be effective at retaining sand.
The lidar image hints at an under water structure between the Walton fort ruin and the scour channel. It is undoubtedly something that was built before the 1700s when the area was inundated. If it did not appear on maps or drawings of that time it was probably already buried under sand, it might be a road or walls from the Roman or Norman period. Where it extends closest to shore is approximately where the scuba club found a pile of red bricks. What I have labelled as “scour channel” might be the Roman era streambed. It would not be unreasonable to assume that there were out-buildings or a village near the fort walls.
Fascinating! I wish that I knew more about the Lidar world; undoubtedly the datasets created for flood planning contained very detailed aerial images, if one could but extract them.
LiDAR is not necessarily associated with imagery. There are datasets where we have the laser returns but no images associated with them. It is a very expensive skill to practice, Merrick MARS which is a software to visualize and treat LiDAR for example costs $5,000 per license to own. There are a few free viewers, and CloudCompare is an open source software that can be used to display and manipulate LiDAR datasets, albeit in a limited fashion. Now in Europe national mapping agencies are collecting nationwide datasets for things like high precision digital elevation models, forest biomass mapping (very important in Scandinavia with its logging industry) and wetland mapping. The EU has been pushing to make the datasets available for free to the general public as part of the INSPIRE initiative but the national governments have been pushing back. There are also military issues behind the push back: high resolution maps of Greece’s border regions are classified, and thus some data coming out of it like soil maps are also classified, though they are available for a good reason and after a lot of bureaucratic hurdles.Water is transparent in some wavelengths and this is used is coastal bathymetric mapping, but IIRC only as far down as 10 m or so. If you are trying to find sunk cities in the bottom of the sea, try sonar
Thank you – this is all a new world to me.