Overview

Students analyze simulated radar data to map surface elevations on a grid. Next, they determine what kind of surface feature is displayed by the data. Students then build a physical model representing their data.

Materials

Colored pencils, crayons, OR markers (six colors)

Student data sheets – Download | View on Google Docs

Teacher answer key – Download | View on Google Docs

(Optional) plastic building bricks, soft kid clay, or 3D design software

Management

• The suggested materials or other materials can be used for modeling features depending on availability or student abilities. See images below for examples.
• Colors that take into account student color-blindness should be used as appropriate.
• Provide different data sheets to groups so the class can see a variety of terrains.

Background

Spacecraft can collect data about the surfaces of planets, moons, and asteroids using radar (radio detection and ranging) and lidar (laser imaging, detection, and ranging).

Both methods send a signal – radio waves in the case of radar and laser pulses in lidar – from a spacecraft and measure the returned signal that bounces, or reflects, off a planetary surface. The longer a signal takes to return, the farther it has traveled, indicating a lower surface. A shorter return time means the signal bounced off of a surface with a higher elevation. Meanwhile, the amount of energy returned can provide information about the properties of the reflected surface.

Compare these two views of the farside of the Moon captured by the Lunar Reconnaissance Orbiter. What do you observe in the topographic view on the right that's not revealed in the monochrome version on the left? Image credit: NASA | + Expand image

Spacecraft circling a planet measure strips, or swaths, of the surface as they orbit, eventually mapping the entire body. NASA’s Shuttle Radar Topography Mission was one of several that did this for Earth while the Mars Global Surveyor used lidar to map the Red Planet. Some spacecraft fly by planets and moons, only mapping sections of the surface. For example, the Cassini spacecraft mapped multiple swaths of Saturn’s moon Titan during its more than 13 years at the ringed giant.

This mosaic of images captured by the Cassini mission during several flybys of Saturn's hazy moon Titan, clearly shows the paths, or swaths, of data collected by the spacecraft. The swaths were given a specialized color scheme to emphasize the contrast between radar-dark areas believed to be lakes and seas (shown in blue and black) and the relatively radar-bright dry land areas (shown in shades of brown). Image credit: NASA/JPL-Caltech | › Full image and caption

Procedures

1. Ask students to think about what kinds of natural features there are on Earth’s surface (e.g., mountains, valleys, canyons, plains, etc.).
2. Ask students if they think those types of features exist on the Moon or other planets. Show them pictures of places like Olympus Mons and Valles Marineris on Mars or Maat Mons on Venus.


These two views of Mars' Valles Marineres show the canyon as it appears to the natural eye (top) and as a topographic map (bottom). Image credit: NASA/JPL-Caltech | + Expand image

3. Explain to students that scientists use radar to bounce radio signals off of surface features to measure their height or depth, similar to the way bats and dolphins use sound (i.e., sound waves) to find the location of objects around them.
   
   
   

   An example swath colored in according to the chosen color scheme. Image credit: NASA/JPL-Caltech | + Expand image

   Try bouncing a ball off surfaces of different heights to demonstrate that the longer it takes for the ball, or a radar signal, to return, the farther away, or deeper a surface is.
4. Show the student data sheets, and explain that each grid square represents a surface area and shows the height of that area.
5. Divide students into groups and provide each group with data sheets containing different maps, or swaths.
6. As a class, you will need to decide which colors will correspond to which heights on the maps and fill in the grids with the appropriate colors. Many maps use blues and purples for low elevations, oranges and reds for high elevations, and greens and yellows in between, but feel free to make it your own and consider colors that account for color-blindness.
7. Have each group color in the squares to create their elevation map on the data sheet and determine what feature(s) are shown on their map.
8. Have student groups compare their maps with other groups to determine if their maps might connect, contain similar features, or be separated by missing data (e.g., two maps of a mountain range with missing mountains between the maps). Students should arrange maps relative to other student maps, if appropriate.
9. Using clay, building bricks, or other methods, have students create physical models of their elevation maps.


A 3-D model of the swath using Legos. Image credit: NASA/JPL-Caltech | + Expand image

Discussion

• Ask students to describe or explain the limits to the accuracy of the maps.
• In what ways is this sort of information useful to scientists?
• If you were searching for a landing site for a future spacecraft, which location would you choose if you could guarantee landing in a 6-km-by-10-km ellipse? Where would you choose if you could guarantee landing in a 4-km-by-6-km ellipse?

Assessment

• Student maps should accurately represent the data provided.
• Students should be able to identify which type of surface feature their map represents.
• Physical models should accurately represent the data and maps.

Extensions

• Students familiar with or interested in learning conditional formatting in spreadsheet software can transfer the data to a spreadsheet and format the cells to highlight in different colors based on the data provided.
• Allow students to generate their own simulated data that describes a feature on the blank data swath.
• Surface features, even enormous mountains, are quite small compared to the size of a planet or moon. To see details and features more clearly, scientists use a technique called vertical exaggeration, a means by which vertical height is multiplied by some amount while the horizontal measurements remain the same. This may be listed as a ratio, such as 15:1 or described as 15x vertical exaggeration.
  
  In this video, the vertical exaggeration changes from 1X to 3X to demonstrate this technique.
  
  The simulated data in this activity represent 1 km per unit in each direction (10 km along the short axis, 20 km along the long axis). Using their physical model, have students calculate the vertical exaggeration of their model using the following method, where: a = true feature height from the data swath; b = true width of the data swath; c = feature height on model if there were no vertical exaggeration; d = measured width of model; v = vertical exaggeration factor; and f = measured height of model.
  
  

  a/b = c/d
  c * v = f
  v = ___

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