Comments on a Summer Sighting

I note I had not posted on the Loch Ness Monster since October, having posted twice on her "sister" in Loch Morar. So, I wanted to remark on a sighting report made in the Summer at the loch. Gary Campbell, over at his Loch Ness sightings register website, had (last time I looked) registered a total of 13 sightings thus far for 2021. Helpfully, he has split them into two sections, those at the loch and those via the webcam run by Mikko Takala.

The total was eight webcam and five at the loch. I have already made my views on the webcam reports known before and await better equipment for webcam enthusiasts to use. It is one of the in situ sightings I move onto. This was a sonar contact from one of the tourist cruise boats that ply their trade on the loch. The description from Gary's site is brief:

26 August - Benjamin Scanlon was on holiday with his family and took a trip on the 'Nessie Hunter' of Loch Ness Cruises. He spotted something on the sonar on the boat and caught the image below. Captain Mike of the boat estimated it to be 3-4 metres in length, at a depth of about 20 metres, while the boat was in water about 40 metres deep. 

The image captured by Benjamin is shown at the top. Naturally, sonar images have come more into vogue since the fascinating image captured by Cruise Loch Ness a year ago. The skipper of the boat is Mike Bell who posted a better image on Facebook (below) which we can try and make some estimates from. The first thing to note is that a length of three to four metres is estimated to which we address some comments.

I reached out to Mike on Facebook and he answered some questions I posed to him. 

We were maybe around 200m away from the grant tower of Urquhart Castle, heading out to the deeper water. This was around 10 minutes into the cruise and after giving the young gentleman a demonstration of how the sonar works. We were moving at the time doing our usual tour speed and because of this and knowing how fast we go every second, we then use this to give a rough estimate of what size the object is.  I don’t know [how] familiar you are with sonar as well but we also had our gain turned down at the time, which is why the contact looks a little “broken”

As stated before, the horizontal display is a time axis, so no length dimension can be calculated directly without some further information, which is basically how much the boat has moved and how much the sonar contact has moved relative to each other. This is not a snapshot of the entire object, rather it is a continuous sequence of snapshots merging into a single drawn out streak. The best photo analogy would be someone with a long exposure camera snapping a car driving by. The resulting image would be a streak as successive images of the car merge into one long blur. Or, in this case, it may be more like the camera moving quickly past a stationary car resulting in a similar image.

This is quite frustrating and makes me ask if these sophisticated sonar devices have a snapshot option which would send out one or more quick pings to construct one single image and freeze frame display that to give us a better idea of the dimensions of the object. A continuous time display is actually a hindrance. Again I asked Mike Bell if such an option existed, he said he was not aware of it.

I asked Mike for his speed estimate and it was 6.5 knots per hour or 7.5 mph, but actually it is displayed on the sonar display screen anyway. The heading can also be seen on the display as roughly bearing 155 degrees or about south by south east.  However, the same cannot be quite said for the vertical axis which is the depth measurement in metres. Using the gradations to the right (0, 20, 40 and 60m), the maximum vertical extent of the object comes out at three metres or nine feet. Now granted this is not a rock solid calculation either as an object could move vertically up or down during the period of the scanning, causing it to appear thicker than it is.

To add to the uncertainty, the sonar is highlighting the biggest discontinuity between the object and the surrounding water, which is usually from water to gas to water here and usually indicates the lungs or swim bladder of an animal, if indeed it is an animal in view here. Note that animal flesh is largely composed of water and so is not so easily distinguished from the surrounding waters. I say that lungs or swim bladder as the interface between different temperature layers of water is usually blamed for these readings by more sceptical researchers. There is no denying that the thermocline exists and is detectable, my only objection is that it should appear practically all the time to which I asked Mike if the phenomenon was still visible on the return journey to the pier.

His answer was it was not, but neither was the thermocline as they had turned down the gain to filter it out as much as possible. This naturally leads to the question as to how the object would look if the gain was raised? In other words, what is the "true" nature of the image? Gain is defined as the sensitivity of the sonar receiver to compensate for water depth and water clarity. Increasing the gain shows more detail, and decreasing the gain reduces screen clutter. In terms of the photographic analogy, it is a bit like reducing the aperture size, producing a dimmer image and the effect that has on objects in the picture.

That may well affect the vertical estimate of three metres given above which introduces the need to find a suitable frame of reference against which to measure these sonar contacts when certain parameters can be varied via buttons and dials. This procedure is called calibration and it can involve tests such as dropping an object of known size and density to predetermined depths and note its sonar image for a variety of configurable parameters - or a default set. This is a natural question to ask because a three metre deep contact which is assumed to be just the lungs or swim bladder would imply an awfully big cross section for the whole creature.

But what about a skeleton, are not bones denser than water too? They would be but remember it is the discontinuity in density differences that registers on sonar and the transition from gas to water is bigger than from bone to water. But I suspect a skeletal echo return could add to the "fuzziness" of the image. In the absence of calibration, Mike's own size estimate is one based on experience and how the sonar contacts from known objects such as fish compare to this curious and large contact.

So expect more sonar images to appear in the media as we move into 2022. These are to be welcomed and analysed on their own individual merits. However, a form of sonar "fatigue" may well set in at some point as readers get used to this kind of image and then the questions will be asked as to what do we do with these images and what is the next step after that? That is probably an evolving debate.

The author can be contacted at lochnesskelpie@gmail.com