Tag Archives: Equipment

The Making of the Windy City Gigapan

Looking eastward at Windy City, with a person for scale. The gigapanned portion of the outcrop is at right, but two spires of similarly eroded rock outcrop further to the north of the photographed portion. The stake coming out from the outcrop is a marker for one of our temperature/light intensity sensors. Image credit: Carlos Nascimento
Looking eastward at Windy City, with a person for scale. The gigapanned portion of the outcrop is at right, but two spires of similarly eroded rock outcrop further to the north of the photographed portion. The stake coming out from the outcrop is a marker for one of our temperature/light intensity sensors.
Image credit: Carlos Nascimento

In my previous post, I discussed the gigapan of Windy City. However, the making of that gigapan was quite the adventure in field work.

After the Azorella Peninsula gigapan, the unit was packed up and taken back aboard the Braveheart for a trip to the southeast portion of the island. Rough north winds were expected, and with no protection afforded against those winds and swells from Atlas Cove, the ship had to move. Our expedition leader and two scientists not involved in the radio operations left camp and went to ride out the storm south of Stephenson Lagoon. At that time, it had become clear that I personally would not be able to go to Stephenson Lagoon—an area which was an extremely high priority for a gigapan image. I put fresh batteries into the gigapan mount, and sent it on its way. Sadly, in the almost four hours the team had on the shores of Stephenson Lagoon, they did not have an opportunity to take a gigapan. I’ll have to go back for that one!

Upon their return to camp, I knew since they had not attempted any gigapanning that there were fresh batteries in the unit. As the end of the expedition drew near, it was time to get the gigapan done at Windy City. Mid-morning, Carlos joined me for a trip to the outcrop (about 1.4 km each way). Although we didn’t have a bright sunny day, it was dry with a temperature around 5 °C. When we reached the outcrop and everything was set up, I turned on the gigapan mount. Nothing happened. With new batteries and a limited task, I hadn’t brought the whole kit with me. We headed back to camp, arriving in time for lunch.

Several of the rechargeable batteries I had for the gigapan had been sitting on the charger and were ready to go. I tossed those into the battery holder, put it under my arm to keep warm, and headed out with Carlos once again. At the outcrop I set up the rig again. When everything was set to go, I removed the batteries from inside my jacket, and put them into their slot. I powered it on. The LCD display brightened, but displayed an error message: Button-pusher disconnected or plugged in backwards. Cycling the power on and off didn’t fix it. Everything was as it had been before when it worked. Once again, this was a problem I was unable to deal with at the outcrop.

Back in camp, Carlos looked online for a solution while I tried to see if anything was likely to have come disconnected, although our team had been very gentle with the unit. Nothing stood out. Eventually we found online that the error is commonly caused not by a disconnected or backwards button-pusher, but by a low voltage. That made a bit more sense. Out came the volt-meter, and two sets of six AA alkaline batteries were verified to be fresh. One set went into the battery holder, the other went into a storage case. Now that it was late in the afternoon, Carlos had to report for radio duty, but Adam was willing to come with me—I needed this gigapan before the light died, as there was no guarantee that I would have the weather conditions or time to get it later.

Adam and I hurried over to the outcrop, the light already beginning to fade. I set up quickly, got the batteries out from my jacket, and set up the gigapan.

Please, light, stay with us long enough to complete this shot. Please, batteries, keep up your voltage!

It was clear from the beginning that the shot would not be truly completed. Somewhere in the middle either the light would die or the batteries would. Eventually, both did at about the same time. We quickly put everything back into the packs and headed back for camp. It was getting dark, but we arrived just in time for dinner and the start of my shift at the radio desk.

Although it was too late to be of use, I asked on Twitter what some of the other cold-weather folks had done about their gigapans. By the end of my four-hour radio shift, I had responses from @rschott and @callanbentley. Evidently this is a common problem, which is fought by insulating the gigapan unit as well as possible, and using hand/toe-warmers to add a little heat.

I think it’s time to ask Gigapan to make some design adjustments to improve the cold-weather operation of the units. It wasn’t all that cold where I was gigapanning, yet I still couldn’t get 15 minutes of operation on fresh batteries at 3–5 °C.

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Geoscientist’s Toolkit: Pressure Vessels

Pressure vessels ("bombs") used for high-temperature dissolution of zircon.  Image credit: Bill Mitchell (CC-BY).
Pressure vessels used for high-temperature dissolution of zircon. Image credit: Bill Mitchell (CC-BY).

When scientists are measuring the uranium and lead in a rock—specifically in the mineral zircon, found in many igneous rocks—to determine its age (U/Pb geochronology), they need to dissolve the zircon. Zircon is a very stable mineral, so to dissolve zircon, the mineral grains are subjected to acids at high temperatures (~200 °C) and pressures. Thick steel pressure vessels are needed to contain an inner teflon vessel when it heats up and the liquid inside boils.

In the picture above, there are two pressure vessels. On the right of the red marker, a smaller vessel is used when the zircons from one rock sample are being partially dissolved to remove the exterior surface (chemical abrasion). To the left of the red marker, the large vessel is used for the final dissolution, when zircon grains are on teflon racks with individual teflon capsules.

Various Interesting Articles

Thin section photomicrograph of a gabbro, (crossed polarizing filters).  Image credit: Siim Sepp (CC-BY-SA).
Thin section photomicrograph of a gabbro, (crossed polarizing filters). Image credit: Siim Sepp (CC-BY-SA).

There have been a couple of interesting articles I’ve come across recently, which are worth mentioning.

First, Emily Lakdawalla has an excellent summary of the Pluto discoveries from both the American Geophysical Union’s Fall Meeting and the [NASA] Division of Planetary Science meeting. There’s a lot of new stuff there, and it’s pretty exciting.

Second, the Joides Resolution blog (the Joides Resolution is an ocean sediment coring vessel) has a series of posts (1, 2, 3) on geologic thin sections. Not surprisingly, the thin sections pictured are from rocks such as gabbros or sheeted dikes, which are expected in oceanic crust and in ophiolites (oceanic crust exposed on land). There’s a great exposure of the Coast Range Ophiolite just west of Patterson, CA, in Del Puerto Canyon, which is described in a recent blog post by Garry Hayes.

Third, Dave Petley has a great post on The Landslide Blog about the recent landslide in Shenzhen, China. I find landslides fascinating, and always learn something when I read The Landslide Blog.

Heard Island Expedition Update: T-7 Months

Visualization of a proposed Heard Island shelter setup, using two HDT Global airbeam tents.  Each shelter is 20'x21'.  Image credit: Bob Schmieder [?].
Visualization of a proposed Heard Island shelter setup, using two HDT Global airbeam tents. Each shelter is 20’x21′. Image credit: Bob Schmieder [?].

It’s only seven months until the Heard Island expedition leaves Cape Town, South Africa, heading for Heard Island. Preparations are really beginning to get going!

This morning (Minnesota time) we had a conference call with the entire on-island team (such as were able to join). Scheduling that can be tricky, because we have team members scattered around the globe, including from Australia, the US, and Ukraine.

From the conference call, it was clear that things are coming along nicely. We are gaining familiarity at least with the voices of other team members, so that when people are speaking they don’t need to identify who they are. Planning for the shelters is mostly done. Camp layouts have been presented, and are up for argument. Logistics are coming along, but there is a lot to discuss: how much testing of equipment is required, where should it take place, and how do we get the materials from that place to Cape Town in an efficient manner?

For the past few weeks, the satellite link has been worrisome. Although there are two satellites which may be “visible” from Heard Island (in the radio sense, not the optical), they were not very high above the horizon. With terrain being significant on the island (camp is in a valley), and potential for local weather—especially low-layer marine weather—to negatively affect the satellite radio link, we were concerned that there would not be reliable data/phone connection from the island. Our expedition relies on that data link for safety, to keep in touch with off-island expedition headquarters, as well as to help the VK0EK ham radio operations with real-time contact reporting.

Fortunately, while discussing the expedition with satellite service providers, our satellite team found that one of the satellites in the constellation has been repositioned over the Indian Ocean. We will now have a satellite quite high in the sky, and communications are likely to be reliable. Bandwidth may not be very high still, but it’s better than from Pluto.

I’ve been doing some things for the expedition recently, too. Our Bay Area team has acquired laptops which will be used for the radio operation, and I have been helping with software configuration specifications for that. I have also been involved in radio team discussions about how to set up these portable stations—as an apartment-dweller, I know some things about setting up and tearing down stations. Simpler is better, as are plans with fewer moving parts (and less to haul on and off the island).

Last month, I tweeted a live Q&A session, discussing some of the science that has been done (or is proposed) on Heard Island. Check out the hashtag #HeardQuestions for that, and keep an eye out for another Q&A sometime (in a few months).

My physical training continues as well. I’ve been running, biking a little, doing core strength exercises, and stretching a lot more. Yesterday I was even convinced to take part in a 5k run. It has been several years since I last ran a 5k race, and while I’m not in the shape I was ten years ago, I definitely achieved my goals.

With seven months to go, I’m feeling really good about this expedition. Here’s hoping it comes off that well!

Geoscientist’s Toolkit: Lasers

Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, open to show internals.  Image credit: Kkmurray (CC-BY).
Neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, open to show internals. Image credit: Kkmurray (CC-BY).

Lasers are a fairly charismatic tool for scientists to use—using a laser is an obvious sign that science is happening in some way shape or form, especially if the laser has many hazard warnings on and around it.

Their applications, even within geoscience, are quite varied. They put the “Li” in “LiDAR.” Lasers are also used to turn very small portions of rocks into tiny dusty bits, in a process called laser ablation (the LA of LA-ICP-MS).

One tricky problem in geochemistry is that of analyzing rocks with a mass spectrometer. Mass spectrometers work only on ionized gases (or plasmas), and rocks are pretty solidly solids. In order to get them into a mass spectrometer, you need to break them down somehow, either through acid digestion or other dissolution method, or by vaporizing/blasting them with lasers.

Laser ablation works because lasers—particularly pulsed lasers—can emit a great deal of energy into a small volume very, very quickly. As I expect you know, rocks are not especially thermally conductive, so when they are heated up by all the laser energy coming in, it doesn’t have anywhere to go and the small volume of rock heats up and is broken into dust fragments and/or vaporized. By flowing a gas like helium or argon over the sample, this dust can be swept along into the plasma torch of an inductively-coupled-plasma mass spectrometer and analyzed.

Lasers used for ablation can be focused to very small spot sizes, from 2 μm to 1200 μm (=1.2 mm). These spot sizes are small enough that zones within a crystal, such as growth bands or inclusions, can be analyzed separately.

For atmospheric work, lasers can be used for spectroscopy, or at least probe the concentration of certain molecules (e.g. H2O, CO2). One of my favorite instruments (perhaps deserving its own Geoscientist’s Toolkit post) is the cavity ringdown spectrometer, where a laser illuminates a cavity with highly-reflective—but not completely reflective—mirrors containing a sample gas between them. A detector then measures the time it takes once the laser is shut off for the light to bleed out of the cavity (ms). From the ringdown time, the concentration of the gas of interest can be measured with high precision, even at very low concentrations. It’s pretty neat.

Really, there are a lot of geoscience things one can do with lasers: this is just a smattering of those uses of the tool.

Geoscientist’s Toolkit: Fluxgate Magnetometer

Fluxgate magnetometer; coil is around 1 cm in length.  Image credit: Zureks (CC-BY-SA).

The fluxgate magnetometer—not to be confused with the flux capacitor—is a nifty tool for determining the strength and direction of a magnetic field.

It works by using an alternating current to induce an alternating magnetic field in a magnetically permeable core (ferrite core), saturating the core. The magnetic field then induces a current in a secondary winding. My apologies for not having an open-use schematic, but the ones here and here are quite good, plus have a more nuanced explanation.

Absent an external field, the induced current will be equal to the driving current. However, in a magnetic field, one direction will saturate more easily and the other less easily, because the permeable core will be reacting to the external field. As a result, the secondary windings will have a current imbalance when compared to the driving winding, and the imbalance will show up both on the rise and fall of the driving waveform. The imbalance has a frequency of twice the drive frequency. Also, this design detects magnetization in one direction only. For a full 3D characterization of the direction of the magnetic field, it takes three magnetometers, each perpendicular to the others.

One of the early applications of fluxgate magnetometers was the detection of submarines (large metallic bodies). Indeed, through this type of study, the alternating magnetization of rocks along the sea floor of the Atlantic Ocean was discovered, with bands parallel to the Mid-Atlantic Ridge. These data gave strong evidence in support of plate tectonics.

Magnetic field anomalies of the world.  Image credit: J.V. Korhonen,J. Derek Fairhead, M. Hamoudi, K. Hemant, V. Lesur, M. Mandea, S. Maus, M. Purucker, D. Ravat, T. Sazonova & E. Th├ębault, 2007, accessed via SDSU.
Magnetic field anomalies of the world. Image credit: J.V. Korhonen,J. Derek Fairhead, M. Hamoudi, K. Hemant, V. Lesur, M. Mandea, S. Maus, M. Purucker, D. Ravat, T. Sazonova & E. Th├ębault, 2007, accessed via SDSU.

But the magnetometer’s usefulness doesn’t stop there! Earth’s magnetic field extends out into space, where it interacts with magnetic fields from the solar wind. By measuring the magnetic fields, scientists can study the interactions between Earth’s magnetosphere and the solar wind, interactions which can give us auroras.

Aurora in Minnesota.  Image credit:  Charlie Stinchcomb (CC-BY)
Aurora in Minnesota. Image credit: Charlie Stinchcomb (CC-BY)

Perhaps an even more exciting application is the study of magnetic fields near the Moon. NASA’s ARTEMIS mission (using repurposed THEMIS spacecraft) is flying two magnetometers around the Moon. Heidi Fuqua, a scientist at UC Berkeley, and her collaborators are using the magnetic data gathered by the ARTEMIS satellites to study the Moon’s interior. Depending on the size and conductivity of the Moon’s interior, the magnetic field will have differing responses to the induced magnetic field from the solar wind. It’s pretty neat stuff!

Geoscientist’s Toolkit: Heavy Liquid Separation

Heavy liquid separation.  Mixed dense (red) and light (purple) minerals are poured into a liquid of intermediate density and stirred.  After they come to equilibrium, the dense mineral(s) will sink, and the light mineral(s) will float.  Image credit: Bill Mitchell (CC-BY).
Heavy liquid separation. Mixed dense (red) and light (purple) minerals are poured into a liquid of intermediate density and stirred. After they come to equilibrium, the dense mineral(s) will sink, and the light mineral(s) will float. Image credit: Bill Mitchell (CC-BY).

When purifying a mineral from whole rock, one of the most useful separations is by density. Water, being less dense than most rock, is not especially useful for this. However, lithium metatungstate (LMT, mixed with water) and sodium polytungstate (SPT, also mixed with water) can create denser—albeit more viscous—liquids, with densities approaching 2.9–3.1 g/cm3. These denser liquids are enough to separate feldspar and quartz (<2.7 g/cm3) from zircon, titanite (sphene), and barite (densities >3.5 g/cm3).

Separations are fairly straightforward. A crushed, sieved rock sample is poured into a separatory funnel filled 1/2–2/3 full with the heavy liquid. The slurry is stirred vigorously with a stirring rod, and allowed to settle (it may take a couple hours if the grain size is fine and the liquid viscous). After it settles, the dense minerals should have sunk to the bottom, while the light minerals will float. A filter funnel is then placed under the separatory funnel. When the stopcock is opened, the dense minerals and some of the heavy liquid will pour out the bottom. The stopcock is then closed when the heavy separate has passed through. A second filter funnel is then used to capture the light fraction. With good filtering, the heavy liquid can be reused. The separates can be washed with distilled water and dried.

Heavy liquid separation is often used in combination with magnetic separation to purify minerals for analysis. Depending on the difference in densities being separated, a liquid may need to be fairly precisely calibrated with larger samples of the desired minerals. Sanidine (~2.55 g/cm3) and quartz (~2.65 g/cm3) need a well-calibrated liquid to achieve good separation, while either (or both) of them from zircon can be done with any LMT solution >2.7 g/cm3.