Sunday, March 6, 2011

Imaging of Yukon Shipwrecks

A year or two ago, the well-preserved wreck of the Klondike-era paddlewheeler A.J. Goddard was found in Lake Lebarge on the Yukon River. The find (which is now protected) got a lot of attention because of the ghostly images (click on the very high resolution pop-up ones here) as much as the historical significance. The wreck was recently in the news again because divers had found some vinyl phonograph records which had the potential to be played. Listening to the music of the dead crewmen of a ship evocative of the Cremation of Sam McGee would create close, perhaps emotional, connection with these poor unfortunates.

Being made of stern stuff (heh) what I am more interested in is the intriguing sonar image (above) that accompanied the mainstream press coverage. The phonograph is cool, but archaeologically the more significant development are the new technologies being used on wrecks in general and some Yukon wrecks in particular.

I found more images and a very short article at Wired magazine and they are worth a look, as is much of the background info from the Institute of Nautical Archaeology (INA), which includes a photo gallery. Edit: you can view a nice video of BluView and OceanGate’s sonar model of the wreck here.

For one thing, I had no idea of the scale of steamboat traffic on the Yukon. The INA notes:

When the Gold Rush exploded, forty-three West Coast shipyards responded to the demand, and in 1898, 131 sternwheelers were constructed in yards as far south as San Francisco, and as far north as Dutch Harbour in the Aleutian Islands. In total, 266 stern and side-wheeled steamboats operated on the Yukon River in Alaska and Canada.

When the boom dissipated in 1900, many steamship companies either went bankrupt or were bought out by competitors, and surplus tonnage was abandoned. Often vessels were left derelict on shore along the banks of the river, where they had been winched out of the water in the fall to protect them from ice damage. As a result, the Yukon now contains one of the greatest intact collections of stern-wheel vessels known, and many are in excellent condition.

This isn’t the place to dwell on the specific history of the A.J. Goddard, which went down in a storm with three souls lost. Rather, the advanced sonar used, the Blueview BV-5000-3D, can be deployed on a small remotely operated vehicle (ROV) and via multiple passes over and around the wreck, a highly detailed, highly accurate, three dimensional model of the wreck is derived. As noted, you can view a video of the sonar model here. Very cool. It would take underwater archaeologists with clipboards a while to replicate the accuracy of this 3-D model, though of course the divers can record many more qualitative variables as they go.

In addition to the AJ Goddard information, the INA has an interesting site about a survey project to record these historic Yukon River vessels, which includes an un-narrated video showing the “point cloud” of an innovative use of LiDAR technology to map the abandoned hulk of the Yukon paddlewheeler Evelyn, more images of which can be found at the INA photo gallery.

LiDAR stands for “light distancing and ranging”, and is basically radar, only using laser beams. It allows scanning of a three-dimensional shape – it can be used from aircraft to make a model of a landform, or on a table top to record the size and shape of artifacts, or at an intermediate scale then buildings or other structures, such as this shipwreck, can be recorded quickly and to very high accuracy. Over 150 million laser data points give a three dimensional model of interior and exterior of this wreck. The video gives a good idea of how three dimensional models can be rotated and “entered” to reveal structure. Water conditions would need to be very clear to replicate this underwater, but then, as seen below, they may well be on occasion. The advanced sonar is more likely to be of general underwater use. More details on the LiDAR survey of the Evelyn is here.

[Read More......]

Source from :

For more interesting topics related to archaeology, visit archaeology excavations.

No comments: