zondag 14 juli 2013

Two historical voyages crossing paths

In one of my previous post, I explained that I am currently working in a project to explain the measurements done by Vening Meinesz, a Dutch civil engineer responsible for high-accurate gravity measurements onboard the Hr. Ms. K18 submarine. He, together with the crew, sailed from Den Helder, Holland to Java, Indonesia. Stopping at harbors along the African, South American and West Australian coast.

At the end of december 1934, the Hr. Ms. K18 left port of Saint Vincent, one of the northern islands of Cape Verde. Cape Verde was also visited by the famous biologist Darwin during his voyage on the HMS Beagle. During this 5 year long voyage Darwin collected many observations that enabled him to establish the evolution theory. A theory that describes the diversity of living creatures and their way of adapting different environments, quite well, if I may say so. 

However this was many years before Vening Meinesz sailed from Saint Vincent. They sailed southwest to the center of the Atlantic Ocean, which is a bit strange if you know that their next port will be Dakar, Africa (which is to the East). Why would they do this? I was looking at some geophysical evidence. It could be that Vening Meinesz would want some nice observations of the mid-oceanic ridge. Remember that the plate tectonic theory was only theorized in the 1960's. 

However I found the direction of the voyage a bit strange. To observe the mid-oceanic ridge best you should sail pure west. Reading the navigation logbook of the voyage I saw that before they reached the ridge, they stayed at a location for one complete day. This was strange because the location had not significant geophysical relevance (just another volcanic landscape). So I decided to read the comments made by Vening Meinesz in his summaries of the voyage. This is what I saw:

Leaving St. Vincent, our route brought us far out into the Atlantic. This loop was due to the crossing of a Dutch areoplane (wow, not aircraft, but areoplane. I like the old times) to the Netherlands West Indies; for providing this plane with the necessary radio-bearings for its position and for giving it indications about the weather, Hr. Ms. K18 was ordered to be stationed for twenty-four hours at a point in the middle of the ocean.

Netherlands West Indies being Curacao. As an Aerospace Engineer, this got my attention. What aircraft? It must be an important crossing, for having the Hr. Ms. K18 have to divert his route. So I did some googling on the web and found the following website.

It was the KLM's maiden voyage to the West Indies. A Fokker F18 (look at the number, both the same!!!) made his 8 day voyage from Amsterdam, Holland to Curacao. The following poster (obtained from the website) shows the route of the Fokker F18:

It states "KLM Christmas Mail Flight to Ned. West-Indie, leaving from Schiphol on 15th of december 1934". The Fokker F18 would eventually land in Curacao on the 22th of December. This would mean that it flew over the Hr. Ms. K18 (number, number) around the 20th, which coincides with the track logbook. If you look closely to the poster (click on it), you can see a small (submarine-shape) figure in the middle of the Atlantic. Could this be the Hr. Ms. K18 with Vening Meinesz onboard? 

The KLM Fokker F18 voyage would be the start of the famous inter-continental airline KLM. Two important voyages in Dutch history crossing paths in space and time, aiding each other. Hr. Ms. K18 provided bearings and weather reports and for the sake of the story, maybe the Fokker F18 transported a Christmas letter for Vening Meinesz which he received on his later visits in South America. The paragraph of his comments did not end and neither did his voyage:

The Navy had consented that the ship, once this duty fulfilled, continued its route for reaching the area of the Mid Atlantic rise and then returned by a different route towards the next port, Dakar. By regularly diving once during the day and once during the night a valuable series of observations was obtained over the whole trip. The soundings over the Mid Atlantic rise showed an irregular topography, suggesting a volcanic landscape. The approach to Dakar provided the writer with a further coastal gravity profile.

The mentioned irregular topography is the old volcanic landscape created by plate motion (not known in Vening Meinesz time), where the age of the landscape decreases towards the center of the rise. I complete this post with the observations of Vening Meinesz (gravity and soundings), such that you can see the scientific value of this voyage. 

In the end I think this crossing of voyages is remarkable and should be remembered.

woensdag 10 juli 2013

Melting of the ice, backwards

A few days ago, two workmen were fixing my sewer and plumbing system underneath my house (It was kinda smelly). During the coffee break (which is the theme in my blog, all good things come from a coffee break), I had to explain what I did at the university. So I explained that I was looking at the motion of the Earth's crust due to ice loading during the late-Pleistocene ice age (well not in those words, and I did not mention, that I was doing this with satellite data, because my experience tells me to leave this part out. If you use the word satellites, people just stop listening and laugh). They found it very interesting ;).

I know, it is an abstract subject and difficult to grasp (it took me several months to fully understand the complexity of the problem, I am still working on how to solve it). Last week I needed to look at the ice sheet, that caused the motion of the crust that we observe today. People have made models on the growing and melting of this ice sheet, using all kinds of observations, from markings on rocks, bird droppings and pre-historic campfires. One of these models is called ICE-5G, constructed by W.R. Peltier from the Department of Physics in the University of Toronto, Canada.

To get a feeling that an ice sheet can deflect the Earth's crust, you should first get a sense of magnitude of this ice sheet. Therefore I made an animation that shows the growing of the ice sheet until its largest magnitude 21,000 years ago (21 ka). The animation starts with the present and goes back in time with steps of 500 years. The color scale illustrates the thickness of the ice sheet, going up to 3 km (that is a lot of ice).

I have not plotted topographic height variations, because I want to emphasize the ice sheet thickness (oh, and really watch the movie at 720p HD).

The movie starts with the view of Northern Europe. The current ice sheet of Greenland is visible and a little bit of ice on the Russian island, called Nova Zemlya (a very important island in Dutch history). The first 8500 years back in time does not show any ice in North Europe. So it gives you some time to orientate yourself. The viewpoint rotates around Scandinavia from Canada and ends in Russia. you see Scandinavia in the middle. 

When going further back in time, some ice is visible in Sweden. Also the ice on the island Spitzbergen grows a little bit. This growing (or melting, because we go back in time, get it?!?) continues and even ice in Scotland is accumulating. The Last-Scottish ice sheet peaks at 13,000 years ago, but vanishes again, when we continue to go back in time. The ice on North Europe, Iceland, Spitzbergen and in the Barentz Sea, however, keeps on growing. 

The Scottish ice sheet reappears 15,500 years ago (or melts away, keep focused, its so confusing.) and continues to grow. Eventually it will be connected to the big ice sheet on top of Scandinavia. This ice bridge is resting on the continental plate underneath the North Sea. Oh yeah, there is a large spike at 18,000 years, but I think this is a glitch in the model/processing (I don't believe in extreme local snowfall), ignore it. 

21,000 years ago the North Europe ice sheet is at its largest. In all its glory pressing down on dirt, rock and crust. This impression, this footprint is still observed today as very small land uplift rates and gravity field changes.

maandag 1 juli 2013

Do it yourself physics: Determining the curvature of the Earth, if you have better equipment

Working on this new project, see previous post, made me enthusiastic to do some gravity experimentation myself. I wanted to see if I can measure the curvature of the gravity field of Earth myself. I only needed a gravimeter (fancy word for very precise accelerometer).

Me, being a 'not-paid-much-just-enough' PhD researcher, I can not buy a very precise gravimeter, but I do have a laptop which contains three accelerometers to protect my harddisk in case of a joint meeting of the laptop and the ground. I wanted to see if I could use these for my little experiment (instead of going on an 8 month dedicated submarine voyage with state-of-the-art instruments, hmmmm, what was I thinking).

My laptop is a Macbook Pro (ok, don't start the discussion about which operating system is better. In the end it is all about the person using it) and I found the following code to (pretty easy) access the accelerometer data. The website for reading the accelerometer data gives a nice and clean syntax description on how to use it. You should download the SMSLib package and unzip it somewhere you want it to be on your computer. Then go, using terminal (unix commands), to the directory where you unzipped the package and give your computer the following command:

./smsutil -i0.1 -c100 -atxyz > testcapture.txt

And try to move your computer in some noticeable way (this gives better data and it gives you a sense that it is working). This commands tells your computer to capture every 0.1 seconds (-i) for 100 samples long (-c, this means ten seconds) measurements from the accelerometer and print it (-a) in the following order:

time x-axis y-axis z-axis

This can be varied in all different ways (-atzyx -atz -axyz, and so on). After the computer is finished, you can check your data, by typing:

less testcapture.txt

First column is time after enter, followed by the three read-outs of the accelerometers. If you did move your computer, the read out will have quite some variations. If you did not touch your computer (what I did), you will see that the z-axis will be close to 1 and the other two close to zero (if your screen made a 90 degree angle with the table top, and the table top was level). The numbers will vary a little bit in time, which is the noise of the accelerometers.

Finding out what the noise of the measurement equipment is always the first thing you should do. So I did not touch my computer and turned on the recording of accelerometer data. Then I calculated the magnitude of of the acceleration vector (math!) and plotted it against the variation of the normal Earth.

This was a little bit of a set back. The accelerometers in my computer are noisier (blue curve) than the variation in the normal Earth signal (red curve). Also the acceleration resolution was almost as big as the normal Earth signal variation itself. These sensors just can not do the trick for my experiment. Maybe it is time to buy pendulum equipment like Vening Meinesz and ask the navy if they have a spare submarine...