My post-lockdown commute back to work

[Dillinger]

I'm in the same boat as you at the mo Mendy, here grab my wooden oar and sing us a shanty .

[Mendip]

I'm in the same boat as you at the mo Mendy, here grab my wooden oar and sing us a shanty .

I'm not grabbing anything mate.

This thread started to show my commute to work, but I guess a commute is to work and back home again... and who knows when that could be.

So, apologies in advance but this could be a long thread... I'm just gonna keep on going, maybe for months. I'm not at all sure I'll be able to get back home to Korat this year.

How to fill it? I think the topic of masturbating has been exhausted (at least I hope so) so how about a bit about work? I think Ootai at least may be interested while he has his morning coffee in Isaan... (lucky bugger)

Anyway...

For seabed mapping projects we collect three main types of data... multibeam echosounder, side scan sonar and sub-bottom profiler. The relevant sensor equipment is usually fixed to the ROV but may be towed behind the vessel or mounted to the vessel hull.

First up... multibeam echosounder. I guess most people are familiar with an echosounder a ship uses to find the water depth. A sound pulse is sent down to the seabed, it bounces back and the two way travel time of the pulse is measured. You know the speed of sound through water, so it's easy to work out water depth. A multibeam echosounder works the same way, but a constant stream of hundreds of sound pulses in narrow beams are sent in an arc to the seabed from the ROV, and the time taken for each sound pulse to return is measured. A typical frequency may be around 450 kHz.

A map of the seabed can be produced from the multibeam echosounder data.

Here's the typical seabed from northern Norway. The huge furrows are iceberg ploughmarks, formed maybe 10,000 to 12,000 years ago at the end of the last glaciation when the ice shelf broke up. The ice became mobile and icebergs drifted about, dragging their bottoms through the seabed (sea level was maybe 150m lower in this part of the world back then since so much water was locked up as ice). These ploughmarks maybe many tens of metres wide and 10m or so deep, and each one marks the path of an ancient drifting iceberg. These will have obvious consequences to the lay comfort of a pipeline and influence route design.



Shipwrecks can be detected by the multibeam echosounder, although side scan sonar is the equipment of choice for searching for debris, shipwrecks, or more recently aeroplanes on the seabed. For aeroplanes you're looking for the engines... they are generally the only recognisable component to remain intact on the seabed after a plane hits the sea and breaks up.

Here's a 65m long shipwreck we found a while ago almost across a proposed pipeline route we were surveying. The route had to make a slight detour. Wrecks don't look great in echosounder data.

It's always a strange feeling to find a shipwreck as it may well mark the place where people have died. This one was probably a fishing boat and if it went down before radio, then as far as people on land were concerned it would have just disappeared. There may be some family on the west coast of Norway who talk about Great Grandad Sven-Ole who disappeared in the big storm of 1895... or something like that.

Makes you think...