Vacation time

Sea, sand and sun: what better way is there to disconnect from the ice-filled world of Antarctica? I am leaving to go on vacation today, and will be back in a few short weeks. Posting will probably be irregular while I am away, however, I will try to keep as up to date as possible.

Best summer (boreal summer) wishes to all my readers, be you at work or in the process of enjoying a few days' break. I will be back soon, my batteries charged by liberal applications of solar energy and salt water, ready to pick up where I left off.

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Keep up to date with the latest developments at http://sismordia.blogspot.com

A seismologist's view of thermodynamics

Since when have seismologists been interested in thermodynamics? Personally speaking, thermodynamics was one of my least favorite subjects at university. In the past few days, however, it has become necessary for me to look into it again.

Here is the problem: how to keep our seismic stations running for as long as possible after the sun goes down for the Antarctic winter, when the only power available comes from pure-lead batteries? The colder the batteries get, the less power they can supply. So the problem becomes: how can we keep the batteries warm for as long as possible?

While the sun is up, we can generate power using solar panels, so we can use some of this power to heat the enclosure in which we house the batteries. The amount of energy we dissipate as heat within the enclosure and its degree of insulation will determine the temperature we will be able to maintain the batteries at.

At sundown, we will no longer be able to actively heat the enclosures, so they will start to cool down. The temperature will fall exponentially, until it reaches the outside temperature, approximately -60C, at which the batteries are essentially dead. The rate of the exponential decay depends on the enclosure insulation, but also on the heat capacity of its contents. The batteries themselves will contribute to this heat capacity, slowing down the cooling significantly.

We still need to run some control experiments, but it seems that a combination of good insulation and the heat capacity of the batteries may allow us to keep recording for a non-negligible part of the Antarctic winter.



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Historical seismometers #1 - Wiechert

Modern seismometers are all well and good - in fact most are excellent - but they are not as fascinating as historical instruments. The institute I work at in Strasbourg runs a Seismology Museum that contains a superb collection of seismometers. In this series of posts, I'll be showcasing my favorite ones.


First up, the Wiechert horizontal seismometer, shown in the figure above [photo credit Michel Dufloux]. It is an entirely mechanical seismometer, made in Gottingen (Germany) in 1904, and was in use in the Strasbourg seismic observatory between 1904 and 1968.

It is essentially an inverted pendulum, which records both components of horizontal motion on rolls of smoked paper. It weighs 1000 kg, and has a natural period of 8 seconds. Damping is provided by two air-pistons on the top of the instrument. The pendulum is centered by placing a series of small weights on top of the main mass. This instrument is very delicate to set up and use, but it is truly a work of art.

The Wiechert in Strasbourg is no longer in operation, but is visible in our museum. However, the Wiechert Earthquake Station in Gottingen, which is open to the public, does have a working instrument.

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Antarctic Sea Ice Video

Antarctica is covered in land-ice, and surrounded by a skirt of sea-ice. This latter is not stable, but grows, shrinks and moves throughout the year.

The following is a video published by SCAR (Scientific Committee for Antarctic Research). It shows two full cycles of Antarctic sea-ice growth, compiled from satellite observations.

Antarctic Sea Ice 1994-1995

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Expedition planning #3 - The purchasing jigsaw

Seismic experiments require seismic stations, which don't exactly come cheap. You would think that once funding has been secured, the rest would be easy. Read on to find out how purchasing anything in a university context is like doing a jigsaw puzzle.

Once the funding is approved, it has to be made accessible, i.e. put into a university spending account which you can order from. At this stage, you often have to pre-decide how much of this money will be used for "investment" (i.e. for purchasing items which cost more than a certain amount and which have to be inventoried), and how much will be used for running costs. You had better get this part right, because university accountants will most likely refuse to change anything once it's been decided.

The next step is publishing a public Equipment Search, in which you state what it is you would like to purchase, and give the criteria on which you will judge offers made to you by the various companies which make or distribute the equipment you are searching for. Once the search is officially over, you must chose one of the competing bids, and justify your choice using the criteria you published in the search itself.

Then you can have a purchase order made out by the university. This requires the presence of a person qualified to draw up the order (this is not left to scientists - oh no!), and of the person who is responsible for the university account being used to make the purchase (which is often a senior scientist). Of course, the probability of both of these people being present at the same time (or at least soon after one another) is a function of the distribution of public holidays, and the of tendency of people to go on vacation. This latter factor is the most important one during the months of July and August.

Then, finally, you can send off the purchase order, arrange for shipping to a customs broker, and arrange for the customs broker to deliver when the university will be open again after the holidays. You hope, of course, that delivery will be made in time for you to test the equipment you have purchased before sending it on to the underside of the world for your crazy seismic experiment in Antarctica.

If you think this is more than enough to give you a head-ache, you are not alone! Maybe once I'll have done this a few more times it will all seem easier. For the moment, it's not fun at all...

[Image credits: Weston Boyd]
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