Seeing What You Can't See

Overview

Have you ever wondered how polar scientists do it? How do they really know if the planet is losing vast quantities of ice anyway? You can use pictures from satellites to monitor the surface from year to year, but the vast majority of ice is hidden from view, buried beneath the surface in some of the most inhospitable and inaccessible corners of our planet. NASA’s Operation IceBridge is the largest airborne survey of Earth’s polar regions ever conducted. The mission flies a sophisticated array of instruments, including high resolution cameras, LIDAR for surface mapping, ice penetrating RADAR, and a magnetometer and gravimeter, onboard a P-3 aircraft previously used by the Navy to hunt submarines. This impressive array of instruments allows scientists to see beneath the ice without ever leaving the airplane.

Objectives

1. Students will improve their understanding of the NASA-IceBridge mission and how instruments are used to determine the terrain underneath the surface of the ice.
2. Students will be able to use Microsoft Excel to create 3-D surface plots and interpret these plots.

Lesson Preparation

Note: The activity is designed as a classroom activity so you’ll need one set of materials for each group of students. It’s ideal to have students work in groups of two or three at most.

Step 1: Making up the mystery box!

The first thing that needs to happen is Mystery Boxes need to be constructed. I like to let my students design the boxes because it turns into a bit of a competition with other groups in the class … who can figure out what’s inside the other boxes? It’s best to have the boxes made up the day before measurements are made so that the glue has time to dry, but if you’re rushed for time, you can always have students tape the items in the box as well.
Each student group should include between two and four items in the box depending on available space. The picture to the left gives you an example. In this case I used a roll of masking tape, a piece of wood, and 1/2 of a foam ball. Once all of the items are in place and secured, seal the box with tape so that it can’t be opened.

Procedure

Step 2: Relating the Mystery Box activity to Polar Science

• Consider the information above about MCoRDS and other background from the IceBridge Mission website provided at the beginning of the lesson plan.
• Open a discussion with a question, "How do polar scientists know what’s under the surface of the ice?" "How do we actually know if the thickness of the ice is changing?"
• Distribute the sealed boxes to the groups and if you had students design their own mystery box make sure they don’t get the one they built.
• Spend some time discussing how they could determine what’s in the box. Give them three rules: They can’t open the box, they can’t distort the shape of the box in any way, and they can’t shake the box.

Step 3: Observations and Measurements

• After sufficient discussion has taken place, have students tape the graph paper (attached) to the top of the box.
• Measure the height of the box in ___ mm and record this value.
• Using the bamboo skewers punch a hole big enough for the opposite end of the skewer to fit through the hole in the center of each square (see picture attached).
• With all the holes punched through, drop the skewer (non-pointed end down) through each hole and measure how far it goes into the box before it stops (hits something). Measure and record the depth in ___ mm.
• Height of the surface in the box __ mm = Height of box __ mm — Depth Skewer goes into hole __ mm
• Record the “height of surface in the box” in ___ mm at each square. I usually just record the value on the graph paper next to the hole in the center of each individual square.

Discussion

Ask students how the task they just completed is similar to the MCoRDS radar system used by IceBridge. Snow and ice penetrating radar onboard the aircraft fires about 12,000 pulses per second. Measuring the surface underneath the ice and snow. Each of these pulses is analogous to the measurements students made by dropping the bamboo skewer into each of the holes. Now to make sense of it all.

Step 4: Entering the data into Excel

Note: If you do not have access to Microsoft Excel you can have students color each square on the graph paper based on it’s height (e.g. squares with height between 10-15 mm are green, 15-20 mm yellow, 20-25 mm orange, etc.), or you could have them make a model of what’s inside the box out of clay, etc.. I like using Excel to generate a computer model because scientist primarily use computers to model such data.

At this point each of the squares (cells) on the graph paper should have a "Height value" in mm. The graph paper I provided is set up just like an Excel Table (rows are numbers and columns are letters). Have students enter their data into a normal Excel worksheet. See the example in the images attached. Stop! Before you let them open the box and see how close they were . . .

Discussion

Before they open the boxes there are a few things you should do first. Have student groups use MS Word or some other word processor to prepare a report of what they think is in the box. The report should include the following: * Their name and identification * Screen shots of their 3-D surface plots used * A discussion of why the surface plots and any other evidence they used during the process brought them to their eventual conclusion. * What they think the items in the box are and what they are made of. Students may have noticed that some of the items in the box were spongy while others were solid, etc.

Closing Questions

Are there other types of analyses that we could have done to provide more information or different information? (e.g. use a magnet to see if what’s in the box was metal, tap on the bottom of the box and listen the sound made at different spots, etc.) Discuss other instruments onboard IceBridge and how they compliment the MCoRDS. For example the magnetometer is basically a giant metal detector. So in a similar way students would use a magnet to look for metallicity of objects in the box, IceBridge scientists and engineers use the magnetometer to search for metallicity in the rocks underneath the surface of the ice. What other instruments are used by IceBridge to determine the shape of the surface of the ice and/or what lies below?

Extension

N/A

Resources

• PolarTREC Mission Website: http://www.polartrec.com/expeditions/airborne-survey-of-polar-ice
• NASA IceBridge Website: http://www.nasa.gov/icebridge
• See attached images and background information

Assessment

The prepared report and graphs can be used for assessment.

Credits

Tim Spuck, tspuck [at] hotmail.com