Sunday, August 31, 2008

Sunday Seismometer #11

Peterschmitt (1950)

Continuing our mini-series on electromagnetic seismometers (see the Galitzine and Press-Ewing posts), here is a seismometer you are unlikely to see anywhere else. The Peterschmitt was designed and built in Strasbourg in 1950, where it was in use until 1975.

This admittedly ugly looking beast is a prototype classical electromagnetic seismometer (you can see its coils on the near side, very similar to those on the Galitzine instrument) combined with a galvanometer. It has a natural period of 1s, and its amplification is provided by a resistance bridge. The most interesting feature of this instrument is its original inbuilt calibration system.

The design of this instrument is attributed to Elie Peterschmitt, who was recruited by Strasbourg in 1937, took charge of the Strasbourg historical seismological station as well as the stations of Besançon and Bagnères de Bigorre, and later helped develop the European-Mediterranean Seismological Center (EMSC).

Thursday, August 28, 2008

On batteries and aeroplanes

Earlier this week I wrote about space-crafts with thermostatic skins, implying this kind of technology could prove to be useful for temperature control in low-power autonomous seismic stations in the Antarctic. Here is another technological achievement that may be of some use.

The BBC reported over the weekend that a UK-built solar-powered and unmanned plane, the Zephyr-6, had stayed aloft for more than three days, running though the night on batteries it had recharged during the day.

The Zephyr weighs 30kg and flies at an altitude of over 60,000 feet. Its power derives from solar power generated by paper-thin amorphous silicon solar arrays glued over the aircraft's wings. This power is stored in a new type of lithium-sulphur battery.

A lot of effort has gone into power storage and light-weighting the systems. Lithium sulphur is more than double the energy density of the best alternative technology which is lithium polymer batteries. Mr Kelleher, Qinetiq (UK defense and research firm)

These batteries are made by the Sion Corporation:

The custom built Li-S battery pack was designed and assembled by SION Power and consisted of 576 cells built into a battery configuration of 12 cells in series and 48 in parallel. The battery utilized SION’s unique, high specific energy Li-S cells (350 Wh/kg). At ~10 kg, the Li-S battery pack was carefully engineered to minimize total pack weight.
In addition to providing flight power, the battery pack supplied power to a special
internal pack heating system to maintain the batteries at 0oC throughout the cold nights. Sion press release.

The Sion battery data-sheet is available here: sion_product_spec.pdf.

The usefulness of this kind of battery for our stations in Antarctica would depend on its adaptability to long-duration low-power applications, and on its performance at low temperatures. Yet another thing to look into this fall!

Tuesday, August 26, 2008

Funky thermostat film for spacecrafts

You may remember that keeping our antarctic instrumentation at a constant and not-too low operating temperatures is a major challenge. Some time ago I posted about the heating / insulation strategy we implemented in last year's prototype stations. I'm planning to write a short piece on how that strategy worked out in the next couple of weeks.

The subject of today's post is an innovation in thermostat technology that has just been presented at the 236th American Chemical Society' National Meeting in Philadelphia, and that was brought to my attention by the BBC News website.

Spacecraft have a serious problem with temperature regulation, as they operate in blazing sunlight, in the cold shadow of the Earth, or in even more extreme conditions closer or further away from the Sun. As operating conditions vary, so does the amount of heat generated by the onboard electronics.

For large spacecraft, [temperature control] is done with mechanical louvers—basically glorified window blinds—that open and close to allow in or reflect heat. But as satellites get smaller, these systems get too heavy and bulky. - Prasanna Chandrasekhar of Ashwin-Ushas, an American tehnology firm

Chadrasekhar and his team have developed a "skin" that can be placed on a spacecraft to actively control the amount of heat that it radiate by controlling its emissivity.

Polymers in the skin change their emissivity when electricity is applied to them, retaining heat in cold conditions and radiating it away in hot ones. That leads to an active temperature control that can be maintained with very little power.

The skin is just a few tenths of a millimetre thick, has been tested to withstand the rigours of the vacuum and temperature extremes of space, and can be bent and cut to fit craft of any shape without losing its properties.

Would such material be useful in Antarctic conditions, which are much less extreme than those experienced in outer space ? The answer will depend on the amount of energy required to power the emissivity-regulating skin.

Energy is a serious problem in Antarctica given the duration of the winter night. Should the new skin system be as low power and low-cost as announced at the conference, then its use in Antarctica may well be possible. We shall be keeping a lookout for updates on this product!

Saturday, August 23, 2008

Sunday Seismometer #10

Press-Ewing (1953)

Some 40 years after the Galitzine electromagnetic innovation, the same principles of operation are put to work in the Ewing-Press seismograph, built at the Lamont Geological Observatory of Columbia (now the Lamont-Doherty Earth Observatory) by Maurice Ewing and Frank Press.

In the photo below you can see the vertical Press-Ewing instrument on display at the Strasbourg Seismological Museum. It was in use in Strasbourg from 1963 to 1975.

It is an electromagnetic seismograph, coupled with a galvanometer, and has a natural period that can be selected and fixed up to 30s. Recording was optical, on photographic paper. The glass ball you can see on the near side of the instrument reduces the effect of variations in atmospheric pressure on the seismograph recordings, using the Archimedes principle.

This seismograph and its horizontal counterparts are very well adapted for the recording of surface waves. In 1957-58, Press-Ewing instruments were deployed in 125 locations around the globe to establish the World-Wide Standardized Seismograph Network, the first global earthquake monitoring system.

Sunday, August 17, 2008

Sunday seismometer #9

Galitzine (1910)

All the seismographs we have discussed up to now (Reuber-Paschwitz, Reuber-Ehlert, Wiechert horizontal and vertical, Mainka, Vicentini, 19-Ton, Mintrop) have been mechanical, with either mechanical or optical recording. Today's instruments, built by Galitzine in St Petersburg (Russia) in 1910, are the first examples of electromagnetic seismometers.

In the above photograph of the vertical Galitzine (mass 10 kg, period 24 s) you can see the new element of this seismometer: the coil placed at the end of the pendulum's rod. This coil oscillates in a magnetic field, and creates an electric induction current which can be measured using a galvanometer.

A copper plate, fixed on the same rod as the coil, oscillates in the field of a second magnet and provides damping via a Foucault current.

The horizontal instrument (above, mass 7 kg, period 12 s) works using the same principle. The object placed in front of the seismometer is a galvanometer that is equipped with a mobile frame and a mirror for optical recording.

The Galitzine instruments amplify Earth motion in two successive stages: an electromagnetic amplification (the galvanometer mirror rotates more than the pendulum oscillates) followed by the optical amplification caused by the distance between the galvanometer mirror and the recording medium.

Sunday, August 10, 2008

Sunday seismometer #8

Mintrop (built sometime after 1910)

From the very large (last week's 19-ton seismograph) to the relatively small : the Mintrop portable horizontal seismograph.

The Mintrop is an odd instrument, that measures horizontal motion using a damped inverted pendulum with a horizontal rotation axis. Its relatively small mass is coupled with a vertically oscillating mirror and an optical recording system.

Given the delicate nature of the recording system, the Mintrop must have been rather difficult to install. It is considered to be one of the first portable field instruments, and was used for early prospection studies by German oil companies.

Wednesday, August 6, 2008

Quake Catcher Network

Thanks to Julian over at Harmonic Tremors whose post about last Tuesday's M5.4 earthquake brought the Quake-Catcher Network to my attention again (I originally read about it on Geology News and Highly Allochthonous earlier this year, but did not have time to blog about it).

The Quake-Catcher Network is a collaborative initiative run jointly by Stanford and UC Riverside that aims to use acceleration detectors present in most modern laptops to form a low-cost strong motion seismic network.

Laptop users can download a client program that sits and monitors the motion of their laptops, sending information to the Network when any strong signals are detected. If strong signals are detected by many nearby laptops at the same time, the Network knows an earthquake is happening.

Laptops continuously move with the people who use them. So how does the Quake Catcher Network know where the laptop is? Users can give precise locations (using a GoogleMaps widget) of where they use their laptops most often. To choose between these locations, and also to deal approximately with undefined locations, the Network uses the laptop's current IP address. Nifty!!

As correct time is essential for earthquake location (just ask any observational seismologist or seismic network manager), the Network also checks the laptop's clock to make sure it is on time.

I have just signed up as a Quake-Catcher laptop client. The sign up procedure is completely painless (at least it was on my mac). Quake-Catcher uses a system called BOINC to interact with your computer. This is the same system used by other distributed computing projects you may have heard about, such as SETI@home or LHC@home.

Quake-Catcher aims to become a global strong-motion network, but it can only do so with your help. The more laptops connect to the system, the better. The accuracy of Quake-Catcher detections depends on the number of users located in any given region, so if you want your contribution to Quake-Catcher to be really useful, you should urge your friends, families and colleagues to sign up.

Monday, August 4, 2008

Another Antarctic Earthquake

In November of last year I wrote about an unusually large earthquake (M 5.8) that had occurred close to Casey Station in Antarctica. Earthquakes of this magnitude are rare in East Antarctica, except, it seems, in the Casey region...

Indeed, on July 23rd of this year, another large earthquake (M 5.3) occurred in the same region. The following image is from the USGS and shows the position of this event as an orange star.

This event was recorded on seismometers all over Antarctica. As examples, I have plotted the recordings of vertical ground velocity for this earthquake at stations CASY (Casey), MAW (Mawson) and PSP02 (a POLENET temporary station near South Pole).

The numbers under the station names on the above plot are distances in km from the earthquake. As you can see, the earthquake was well recorded even at distances over 2000 km.

We often say that the Antarctic plateau is virtually a-seismic, meaning there are few if any earthquakes. As you can see for this Casey event, it would be hard to miss an earthquake larger than M5 virtually anywhere on the continent. Smaller events may still be missed, however, and we do not have enough seismic stations in Antarctica (yet) to be sure that they do not occur.

Sunday, August 3, 2008

Sunday seismometer #7

Great Pendulum or "19-Tons"

In the last Sunday seismometer post on the Vicentini seismograph, we mentioned that in order for a seismograph to overcome the friction caused by a purely mechanical recording system, it needs a large mass.

The Vicentini instruments actually have the smallest masses (100 kg for the horizontal and 50 kg for the vertical) of the mechanically recorded seismographs we have described so far. The Mainka instrument has a 450 kg mass, the Wiechert horizontal instrument has a 1-ton (1000 kg) mass, and the Wiechert vertical instrument has a mass of 1.2 tons.

The largest mass of all the seismometers in the Strasbourg museum is that of the Great Pendulum: an impressive 19 tons (that is 19 000 kg)!

Its construction was started before the First World War (1910), when the Strasbourg Observatory was part of Germany. The idea was to build an instrument that would be similar to one installed in Göttingen, a 17-Ton seismograph. After the war, Strasbourg became French, and it was the French director of the Observatory, Edmond Rothé, who completed the construction of the Great Pendulum in 1925.

The mass itself is essentially made up of scrap metal from the War, including 12 tons of axles from military trucks and 2 tons of weapon parts.

The 19-Ton has a natural period of 2 seconds, and records both the horizontal directions of motion, like the Wiechert horizontal instrument. Also like the Wiechert, its motion is damped by air pistons.

The smoked paper recording system was abandoned in 1970 in favor of galvanometric recording. In 1987 the recording system was changed once again to digital recording using displacement detectors.

The 19-Ton instrument is still in working order today, and is a great favorite with visitors to the Strasbourg Seismology Museum.

Saturday, August 2, 2008

Summer vacation is over

With the end of July came the end of my much needed summer vacation. I took three weeks off last month in order to rest, recoup and recharge after this year's travels (7 weeks in Antarctica, and 4 weeks in the Sub-Antarctic islands).

I spent the time mostly sleeping, lazing on the beach, and swimming. This solar recharge should help me find the energy for the coming academic year: five research projects including the second year of CASE-IPY, teaching, and observatory work.

Here is a GoogleEarth image of my summer hiding spot:

While I was still on vacation, Kim posted about a great initiative to federate and publish geological maps from all over the world. The initiative is called OneGeology, and a new version of its portal will officially be launched next week. The current portal is already very easy to use. The image below is a larger scale GoogleEarth image of my summer hiding spot, in which the geologic units from the BRGM 1:1.5M geological map of Europe have been imported from OneGeology.