Goodwin Sands

[steve yates]

Cos LeighB asked. I just saw the request and that the words are upside down and thought no need for him to redo the whole thing, it just needs flipping. I hadn't actually bothered to look at the profiles to be honest, because I think the phenomenon itself is a quite interesting, I wasn't interested enough to pore into the detail. Disappearing and reappearing boats are sexy, the hard scientific details or facts as to why not so much.
But turning your profiles upside down was not my intent, so I apologise for my ignorance.

 

[Tomahawk]

Or...

If the sand is upside down you may be drunk?

 

[Leighb]

I am afraid I just saw the upside down legend and assumed the whole thing was inverted without looking carefully enough. Apologies.

 

[tillergirl]

I admit I rushed it. I can change some of the text round - somewhere in one of the 1800 pages of the manual!

anyway, note the scouring. As I said the V would be much flatter if the ratio of width to height would be more accurate.

 

[AntarcticPilot]

I admit I rushed it. I can change some of the text round - somewhere in one of the 1800 pages of the manual!

anyway, note the scouring. As I said the V would be much flatter if the ratio of width to height would be more accurate.

Depending on several factors such as the geometry of the feature and the beam width of the echo sounder, a narrow feature may be narrower on the sounder than it is in fact. This is because the sounder "sees" the closest point of the seabed that lies within the beam, NOT necessarily the point vertically below the sounder. If the sides of a trough are closer to you than the bottom of the trough, it will give the lesser if the two, narrowing the apparent trough. A vertical step will be similarly displaced towards deeper water.

I spent several years going into this for satellite radar altimeters! The maths is interesting, but fairly straightforward.

 

[tillergirl]

Yes I agree but the image is primarily distorted because the width. It illustrates how a wreck scours and pretty much nothing else. I could isolate the V and see if I can fit the width within the limitations of the image.

Given that I have to replace all the depth kit this winter after the theft, rather than having the two separate single beam kits side by side, I ought to have one aft and one forward. Two single beam are hardly multi-beam but it might be interesting.

 

[AntarcticPilot]

Yes I agree but the image is primarily distorted because the width. It illustrates how a wreck scours and pretty much nothing else. I could isolate the V and see if I can fit the width within the limitations of the image.

Given that I have to replace all the depth kit this winter after the theft, rather than having the two separate single beam kits side by side, I ought to have one aft and one forward. Two single beam are hardly multi-beam but it might be interesting.

The problem is that equipment capable of synthesizing a narrower beam also requires more stringent calibration, to take account of variations of salinity and temperature. Synthesizing a narrow beam means analyzing the phase difference between two or more sensors, which in turn requires good knowledge of the transmission speed and how it varies through the water column. In an area with complex flow patterns, like the Goodwins, that would be a serious problem on its own.

 

[LittleSister]