Follow Up on the Latest Sonar Contact

Following on from the initial post, I was reading through various email/website/forum talk and the emphasis was very much on the skeptical side of the debate. But that is no surprise since most people do not think there is a large, unidentified creature in Loch Ness and so any story like this is going to lead to "natural" explanations.

Of course, there may be a natural explanation, I would not be so fanatical as to class every story as "monster". Where I diverge is in my view that not all sightings are explained by natural phenomenon.

As it turns out the favoured explanation is a submerged log. It's a theory and it sounds plausible and most people would accept that without any further critical thinking and move on to the next thing. I prefer to persist with some critical thinking.

Aside from the rather important question as to whether a submerged piece of tree debris could produce the strength of such a sonar trace, there are some other things to consider.

One skeptical forum summed it up (link here):

"Page 61 of Radford and Nickell’s Lake Monster Mysteries. Jerry Monk, a British hydrographic surveyor notes that when a piece of wood is immersed in water, over time, it sinks. If there is a thermocline, it is possible for the log to float in mid-water on the denser layer of cold water. Or, the log may sink, decay and form methane, which makes it rise again. The log idea, sinking and rising, degassing and sinking again was used to explain the Mansi sighting on Lake Champlain."

The thermocline is an area below the loch surface where the temperature drops rapidly creating a kind of partition between the upper and lower layers of water. For Loch Ness, it is usually stated to be at a depth of 40 meters but could vary between 30m and 60m depending on the season. Interestingly, the thermocline can be seen on sonar scans as well, which leads to the question as to why it is not visible on this particular scan if it is claimed to be buoying up the supposed piece of tree.

This is an open question since it may be a matter of sonar calibration and sensitivity but it does suggest that the "log" (which is 25 metres below the surface) is well above the thermocline.

Note that the quote mentions that the theoretical log would "float" on the thermocline. However, this target is moving at such a speed that the trace soon disappears off the screen. Can underwater currents achieve this rapidity? Yet another open question which suggests a log would tend to drift rather than speed.

Finally, the quote mentions vertical ascent and descent of a log due to water saturation and then gassification and renewed buoyancy from methane gas decay. Aside from the fact that the object moved horizontally, such a scenario is unlikely at Loch Ness. Decay of organic matter happens at very slow rates at the bottom and indeed tests have shown little gas production to stimulate ascent.

At this point, I have tried to contact the witness for his view on the matter and whether the tree debris he has seen in the past matches this. I suspect the answer would be "No". For me, talking to witnesses is important - unlike too many a number of critics who completely disregard verbal testimony (unless to find inconsistencies to discredit them)!

Another "natural" explanation often put forward are echo effects from sonar beams bouncing off the sides and bottom of the loch. These do produce strange effects such as vertical lines but it is unclear whether they would be capable of producing the trace in question and from the moored, stationary position he was at. Regular users of sonar equipment would be able to recognise such a pattern.

Other causes of unusual patterns are boat wakes. However, this would require a boat to pass fairly close by and again would be recognisable to a regular user (though as with side echoes it is unclear that they could even produce the pattern in question).

The Latest Nessie Sonar Contact

They just keep coming thick and fast these Nessie stories. On the back of two intriguing photographs these past four months and a head-neck sighting, a sonar contact has entered the fray.

This story appeared in the Scottish edition of the Daily Mail for Thursday 15th September 2011. It looks like it did not make the UK website of the Mail, so it is reproduced here for those outside of Scotland.

But first the basics on sonar. I do not claim to be an expert but it is an important tool in the hunt for the Loch Ness Monster. However, like normal photographs and pictures, there are degrees of interpretation, misidentification and, yes, hoaxes.

A sonar contact is a picture made from sound waves instead of light waves. The sonar device sends pulses of sound at various frequencies depending on how deep one wants to go. The reflected echo is processed to form a snapshot of the area within the sound beam.

However, being a continuous series of pulses, the sonar picture is more like a film than photograph and each successive echo builds a trail of images as the targets in the beam move. In fact, one could argue it is more like a picture taken with a very long time exposure.

So if an object is moving it will describe a trail of some shape and thickness. This thickness is not the girth or height of the whole object but whatever returns the strongest echo. This depends not on the size of the animal (for example) but the difference in density between the water and the object. In the case of the fish, the greatest density difference is between the swimbladder and the water since it contain much less dense air (or some other gases). The rest of the fish is closer to the density of water than the swimbladder. In the case of mammals and reptiles, one main area of interest would be the lungs.

The Daily Mail story now follows.

THERE is no sign of the trademark elongated neck, or the signature green humps. But the experts believe this almost unfathomable sonar image could be a breakthrough in the hint for Nessie that began in earnest in 1934.

Surrounded by fish, the ‘blip’ has a girth of about 5ft, though there is no way of estimating its length as it was moving. The image was captured by the quick thinking skipper of a pleasure boat who took a picture of the reading while waiting for his customers at Urquhart Castle, in Inverness-shire. Marcus Atkinson, 42, knows Loch Ness like the back of his hand and spends every day on its waters — but said he had never seen anything like this before.

He added: It's very weird. It was obvious it wasn‘t a shoal of fish and it just kept getting bigger and bigger. This thing is completely different from anything I've seen before.’ Mr Atkinson, of Fort Augustus, Inverness-shire, was idling in the bay when he saw the unusual sonar image. He said: ‘it's one of those moments where you just think, “What on earth is that?" I grabbed my mobile phone and took a picture before it disappeared of the screen. it's all very bizarre.‘ Mr Atkinson's picture shows a cross-section of the loch, with the boat itself at the top right of the picture.

The bright green area on the bottom right of the sonar screen is the bottom of the loch, which rises as the boat gets closer to shore. The small green flashes scattered across the monitor are deepwater fish. But the part of the picture that is exciting interest is the long, thin streak - that looks a little bit like a propeller - between the 20 and 25 metre depth markers. The measurements show it is about 5ft thick - but there is no way of telling how long it is as, if the object was following the boat, it would show up on every ‘blip’ of the sonar.


Expert Nessie hunter Steve Feltham said: ‘This is a sonar contact that defies all explanation — it's a huge object. ‘it’s fascinating, because the camera hasn't an imagination — it just shows what's there.’

So ends the account and I wrap this latest sighting with some comments. The first is that the captions editor makes a howler in comparing the elongated pattern to a sleek, lithe plesiosaur. If they had read the article, they would have gone for a different picture for (as said in the intro) this is a trace built up over a succession of sonar pulses.

The other observation is that the stated 5ft girth is not necessarily the complete height of the object because if it is an animal, it will be the lungs or swimbladder being measured. But then, five feet of lung or bouyancy organs points to one big creature.

I presume the five feet measure is taken by comparing it to the 20-25 metre depth scale in the picture above. Using my trusty ruler, I get an average estimate of 2.5 feet "girth" which is still quite a measurement. I would add that if this was Nessie and we assume a true girth twice as much as my measurement (i.e. giving us five feet) and apply classic Nessie proportions based on numerous eyewitness tesimonies and analysis, then a total tail tip to head length would come out as about 30 to 35 feet - which is a typical Nessie size.

So what was it with a minimum girth of 2.5 feet that was moving at a depth of about 70 feet? No doubt some will have a rational, non-Nessie explanation for this odd signal. Was it some human artefact somehow floating at a great depth? Was it a strange effect of sonar bouncing of the underwater sides of Loch Ness? Or was it the famous and mysterious denizen of Loch Ness?

As for us, this goes into our log of claimed Nessie sightings.

ERRATA: I just remembered "girth" is the measurement around an object as opposed to its thickness. So assuming a circular type girth, a rough girth estimate given a thickness of 5ft would be Pi x 5ft which is roughly 16ft.