Tag Archives: Experiments

Lessons Learned at the Regional Science Fair

A young scientist presents in the undergraduate poster session of the American Chemical Society spring meeting, 2007.  Image credit: Ellen Valkevich.
A young scientist presents in the undergraduate poster session of the American Chemical Society spring meeting, 2007. Image credit: Ellen Valkevich.

This spring I had the privilege of being a judge at my local science fair. As a high school student, I had participated in the science fair and it was a huge part of my science learning experience. Now that I am qualified to be a judge, it is time for me to give back while avoiding the trap of turning into the dreaded Reviewer #2.*

I scored quite a few different projects, primarily in Earth & Environmental Science. I was pleased to see the large number of students involved in the discipline, and the interest they showed in environmental monitoring and sustainability. However, I was surprised to see the number of projects which focused on pH, but without understanding of pH of rainwater or the influence of carbonates.

Limited or non-existent access to instrumentation was clearly a limiting factor in many of the projects. That observation leads to a question: what can be done to address the disparity in instrument access and to improve the quality of data being used in science fair projects? I believe the long-term answer to that question is to fund our schools and support the teachers and staff who work in them.

Another solution would be to have students use and analyze publicly available data. In many cases, this cut out some of the hands-on portion of making measurements, which detracts from the overall learning goals. Using publicly-available data also means that teachers would need to be more aware of good data resources and ideas for how to go about analyzing that data—each significantly increasing the work load and responsibilities of the teachers. For research projects, it is important to have a low student:teacher ratio, so that the students can have the support they need to succeed in their project. However, publicly available data allow students to do cutting-edge research with the same tools and data used by professional scientists.

Here are a few examples of low-budget, high-quality data projects that could be interesting:

  • Weather forecast accuracy. Make a daily record of the National Weather Service forecast (for each day forecast) for your area, as well as the almanac data from the closest instrumented NWS station (often an airport). How does forecast accuracy change over time? How accurate is a forecast 72 hours out?
  • Earth-Observing Satellite data. With a constellation of Earth-observing satellites including Aqua, Terra, Landsat (7 and 8), and formerly EO-1, there are mountains of data waiting to be analyzed. Students can look at crop health locally, at glacial changes, deforestation, volcanic activity, wildfires, and a host of other things. Data are freely available, GIS software is freely available, and the data analysis skills are quite relevant in today’s job market.
  • Buoy data. As I’ve mentioned here before, there are several fleets of marine buoys which take various oceanographic measurements, such as conductivity-temperature-depth profiles and current measurements. Oceanography isn’t my thing, but I’m sure there are enough papers that use these data that some project ideas could be found. These projects are likely to use GIS.

* Reviewer #2 is known for being overly critical, wanting a paper that isn’t particularly close to the paper that was submitted, having unreasonable or unattainable expectations, and generally being a jerk.

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The 1991 Heard Island Feasibility Test

MV Cory Chouest the ship used for the experiments detailed below.  Image credit: US Navy (public domain, via Wikipedia).
MV Cory Chouest, the ship used for the experiments detailed below. Image credit: US Navy (public domain, via Wikipedia).

Batten the hatches and hang on to the hand rails, because this installment of science at/on/near Heard Island is going to be a wild ride! We’ll explore a paper entitled The Heard Island Feasibility Test,[1] and along the way we’ll make ports of call in climate science, oceanography, and physics. I encourage you to check out a copy of the paper, either at your local (research) library or online. It’s really well-written! There’s also a pre-experiment lecture given by the study’s lead author which is freely available online, and details the rationale behind the study and the expected results.

In 1991, scientists were concerned about global warming. They were very interested in measuring the ocean temperature—oceans can store much more heat than the atmosphere, so while the atmosphere may not warm quickly in a changing climate, the oceans are likely to capture most of the heat. Additionally, water has a high heat capacity (the amount of energy it takes to raise its temperature by a degree), which is why it takes so long to bring a pot of water water to a boil on the stove.

Measuring the ocean temperature seems fairly straightforward: put a thermometer in the ocean, and log the temperature. Scatter a bunch of stations around the world and it’s done, right? Wrong.

The problem with using a thermometer (or many thermometers) to measure the ocean temperature is that there are many small-scale features which can influence the measured temperature. The variability of these measurements is likely to be quite high, and they each measure only a small place— extrapolating to the whole ocean isn’t necessarily justified.

How, then, can a measurement be made which yields an average temperature over a huge volume of ocean?

Sound. Ocean temperatures can be measured with sound. This is an amazing world in which we live!

In water, the speed of sound will vary depending on temperature, pressure, and (to a limited extent) salinity, and be in the ballpark of 1.48 km/s. With variations in speed of 4–5 m/s/°C, a +5 m°C (0.005 °C) change in temperature results in a -0.1 s change in travel time over a 10 Mm (10,000 km) path.[1] Have an acoustic source emit a signal, measure the signal at a distant receiver, and the time delay will yield an apparent average speed of sound. Shifts in these speeds due to warming of about 5 m°C/yr would theoretically produce measurably earlier arrival times.

Speed of sound measured at various depths in the Pacific Ocean north of Hawaii.  Image credit:  Nicoguaro (CC-BY-SA); data from the 2005 World Ocean Atlas.
Speed of sound measured at various depths in the Pacific Ocean north of Hawaii. Image credit: Nicoguaro (CC-BY-SA); data from the 2005 World Ocean Atlas.

One potential problem with all this is the part about receiving a sound signal 10 Mm away from its source. However, the temperature and pressure profile of the ocean cause a minimum in sound velocity at a depth of 500–1,000 m (for mid/low-latitude oceans). This low-velocity region, termed a SOFAR channel acts as a waveguide or a duct, where sounds within it tend to stay within rather than dispersing.[2] Low-frequency sounds (50–100 Hz)are not attenuated or absorbed much by the water, so long-distance reception of these sounds might be possible.

The feasibility test was designed as a proof-of-concept for ocean-wide acoustic reception. Using powerful low-frequency transducers on loan from the U.S. Navy, the scientists would be able to send the signals and have receivers around the world listening for them.[3] Unfortunately for the scientists, the transducers could only operate to a depth of 300 m. That meant that a high-latitude site needed to be found, where the SOFAR channel—that special place which enables long-distance reception—is much closer to the surface.

Heard Island was chosen as a transmission site, because the direct sound paths (mostly, but not entirely, great circles) would reach across both the Pacific and Atlantic oceans.

No major field work is complete without a little drama, though. Late in the planning and preparation phase, the US National Marine Fisheries Service notified the researchers that permits were required to mitigate threats to marine mammals from the powerful sounds. The Australians (Heard Island is an Australian territory) required the permits too. A second vessel was chartered and biologists were assembled to monitor marine mammal activity and fulfill the responsibilities associated with the permits.

The two ships sailed as originally scheduled on January 9, 1991, but neither the American nor Australian permits had been issued. With a scheduled transmission start of January 26th, there wasn’t much room for delay. Fortunately, the permits arrived just in time: January 18th and January 25th. I bet the scientists were very tense during the voyage from Perth/Fremantle (Australia) to Heard Island.

An unscheduled 5-minute equipment test the day before the first scheduled transmission was received in Bermuda, and shortly thereafter at Whidbey Island (near Seattle, and almost 18 Mm away). Basic feasibility was already shown!

Signals were sent in a 1-hour-on, 2-hours-off pattern. Some of the transmissions were a continuous-wave (CW) 57 Hz tone (to avoid 50 Hz and 60 Hz power noise), while others were a mixture of several different frequencies near 57 Hz. For details on these transmission modes I refer you to the paper.

Transmissions for the experiment were aborted on the 6th day—ahead of schedule—when a gale and 10-m swells caused one acoustic source to be lost from the string and fall to the ocean floor. The other sources were badly damaged. Conditions in the Southern Ocean can make field work there very difficult.

One thing I found surprising, but makes plenty of sense upon consideration, was that rather than staying in one fixed location, the ship towed the sources along at 3 kt (5.5 km/h, 3.5 mph). This makes sense once you think about the wind and waves in the Southern Ocean, and how, to maintain control of the ship, the vessel must be underway. Being broadside to the swell in a high sea is extremely dangerous.

In this experiment, the receivers were sensitive enough to detect the Doppler shift from the ship’s movement. In fact, the Doppler shift combined with the known path of the ship (from GPS) allowed the azimuth of the signals to be determined. For many of the signals, it was on the expected heading (not quite a great circle due to the non-spherical Earth and the inconsistent depth of the SOFAR channel). At Whidbey Island receiver array, though, the signals arrived from a bearing of 215°, not the 230° predicted. In that case, the signal appears to have taken a longer path southeast of New Zealand, rather than through the Tasman Sea and between Australia and New Zealand.

Fortunately for all involved, there was little impact noticed on the marine mammals.[4] Despite the low observed impacts, the authors make recommendations for the Acoustic Thermometry of Ocean Climate project to reduce adverse effects to marine life. Using shorter-range transmit/receive pairs, the total power needed can be reduced significantly. Additionally, with temperate waters having a deeper SOFAR channel, the transmitters can be bottom-mounted at depths of around 0.5–1 km, which will help physically separate them from the near-surface-dwelling marine mammals.

In short, the Heard Island Feasibility Test was a resounding (pardon the pun) success. Ocean acoustic temperature measurement is possible, and measurements were made in the North Pacific for a decade, from 1996–2006.

This paper was a really interesting one, and fairly accessible (scientifically) to someone not in the field of signal processing or oceanography. I enjoyed reading it, and suggest you take a look at it if you’re at all interested. My summary here has skipped over large parts which detail the nature of the propagation and the signal processing aspects.

***
[1] Munk, W. H., Spindel, R. C., Baggeroer, A., Birdsall, T. G. (1994) “The Heard Island Feasibility Test” J. Acoust. Soc. Am. 96 (4), p. 2330–2342. DOI 10.1121/1.410105

[2] This phenomenon is analogous to atmospheric ducting of radio waves, which can cause TV and FM radio stations to be heard far beyond their normal range, and for weather radar to pick up ground clutter far from the station.

[3] This sounds almost analogous to the upcoming VK0EK ham radio expedition to Heard Island, where radio operators (including myself) will have stations around the world listening for their signal.

[4] Bowles, A. E., Smultea, M., Würsig, B., DeMaster, D. P., Palka, D. (1994) “Relative abundance and behavior of marine mammals exposed to transmissions from the Heard Island Feasibility Test” J. Acoust. Soc. Am. 96 (4), p. 2469–2484. DOI 10.1121/1.410120

Preferential Preservation of Phytoliths

Scanning electron microscope image of an elephant grass phytolith after dry-ashing.[1]  Image credit: Benjamin Gadet (CC-BY-SA).
Scanning electron microscope image of an elephant grass phytolith after dry-ashing.[1] Image credit: Benjamin Gadet (CC-BY-SA).

As I was looking through the recently published papers in PLoS ONE (all open-access!), I came across an interesting article on the preservation of phytoliths.[2] It is an interesting and well-written paper, and is quite accessible—both in terms of copyright and of science content.

Plants often have little bits of rock in them, called phytoliths (phyto- plant, -lith rock). Phytoliths are formed within the plant by precipitating SiO2 in a non-crystalline form (opal). These microscopic stones can help maintain the structure of the plant, perhaps among other functions. They also preserve well, because SiO2 (glass, essentially) generally doesn’t react chemically with much in the environment.

Just like with fossilized bones or impressions of leaves, the size and shape of phytoliths can be used to identify the plant (or family of plants) which is producing them. If phytoliths are found in the geologic or archaeologic record, they can be used to determine what kinds of plants were in the area, or were being eaten. They also contain small traces of carbon, which can be used for radiocarbon dating (back to ~40 ka) or 13C isotope analysis.[3]

This paper is looking at what happens to various phytoliths in the archaeologic or geologic record, and whether there are preservation biases (some phytoliths being destroyed more easily than others).

The authors took samples of four different types of modern, living plants. These samples were then burned away in a 500°C furnace, leaving just ash and the microscopic rocky bits. With some further, relatively gentle treatment, they were able to isolate the phytoliths. Some of these phytoliths were mounted on microscope slides and counted to determine the relative abundance of different sizes and shapes.

Isolated phytoliths were partially dissolved for six weeks, and the Si content of the liquid was measured. The partially dissolved phytoliths were dried, mounted on microscope slides, and they too were counted to determine relative abundance of the different sizes and shapes after treatment.

Phytoliths which were small, and had a large surface-area-to-volume ratio, tended to be preferentially dissolved—this is not an unexpected result, but is important. The authors argue that based on the Si solubility, the degree of preservation can be assessed (high Si solubility means better preservation); in situations where the Si solubility is low, some of the more delicate phytoliths are likely to be missing, and a count of phytoliths under those circumstances would yield biased results.

But don’t take my word for it! Read the paper. It’s better written than my short explanation, and a fine example of scientific scholarship.

[1] Parr, J.F.; Lentfer, C.J. & Boyd, W.E. 2001, ‘A comparative analysis of wet and dry ashing techniques for the extraction of phytoliths from plant material’, Journal of Archaeological Science, vol. 28, no. 8, pp. 875-886. DOI: 10.1006/jasc.2000.0623

[2] Cabanes D. & Shahack-Gross R. (2015) Understanding Fossil Phytolith Preservation: The Role of Partial Dissolution in Paleoecology and Archaeology. PLoS ONE 10(5): e0125532. DOI:10.1371/journal.pone.0125532

[3] Looy, C.V.; Kirchholtes, R.P.J.; Mack, G.H.; Van Hoof, T.B. & Tabor, N.J. 2011, ‘“Ochoan” Quartermaster Formation of North Texas, U.S.A., Part III: First Sign of Plant Life‘ Geological Society of America Abstracts with Programs, Vol. 43, No. 5, p. 383.

Geoscientist’s Toolkit: Dilute Acid

Folded outcrop of marine sediments in Berkeley, CA.  Image credit: Laikolosse (CC-BY-NC).
Folded outcrop of marine sediments in Berkeley, CA. Image credit: Laikolosse (CC-BY-NC)

When looking at sedimentary rocks in the field, one of the questions which may come up is whether or not a rock is a carbonate, such as in the outcrop pictured above. Although it is easy to determine that with an electron microprobe in the lab, there is a faster field test method: using dilute hydrochloric acid.

Sedimentary geologists will often carry a bottle of 0.1 M HCl and a watchglass with them in the field. A chip of the rock in question can be broken up and placed on the watchglass. When the acid is added, a carbonate will fizz as the acid releases carbon dioxide. This is the same process which makes a baking soda volcano erupt.

In some of my field work in the Texas Panhandle, I encountered a white layer among the redbeds. This bed was not gypsum, as many of the other white beds were. Because I was looking for volcanic ash deposits, not carbonates, an acid test was performed in the field. Unfortunately for me, the ground up sample started fizzing, so I knew it wasn’t the volcanic ash I wanted to find.

Geoscientist’s Toolkit: Gas-fired Tilt Furnace

When you need to make something really hot—1350 °C—a tilt furnace can be a great tool. This is especially true if you are an experimental volcanologist. At Syracuse University, faculty in the geoscience and art departments have teamed up to make actual lava flows on a small scale.

One of the major risks in studying volcanoes is that it can be hard to stay safe while studying them up close. This gets particularly true if there are interactions between the lava and snow or ice, which can cause flooding, explosions from rapid vaporization, and other unpleasant things.

However, by using a tilt furnace, small batches of rocks (basalt) can be remelted and poured under controlled circumstances. This allows studying what happens when lava flows over an ice sheet (video above), or even what happens underwater when lava comes up from the seafloor (video below), where structures called pillows are formed. Small-scale experiments like these can help scientists understand what determines which shapes the lava will take on under which conditions (slope, effusion rate, temperature).

More on the lava project.