EXPLORE! A Cooperative Project of the Lunar and Planetary Institute, NASA's Office of Space Science and public libraries

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1 EXPLORE! A Cooperative Project of the Lunar and Planetary Institute, NASA's Office of Space Science and public libraries Activity: Remote Sensing: Mapping Other Worlds Level: Grades 5-8 To Take Home: False Color Image of Simulated Planetary Surface Background Information Remote Sensing Remote sensing is the process of obtaining information from a source without actually coming in contact with that source. The human eye is a remote-sensing device, and so is the ear. In planetary science, a variety of sensors onboard satellites and spacecraft gather data about the planets. Visible light, a particular wavelength range of electromagnetic radiation, passes over a distance until it encounters and is captured by sensors your eyes which then send a signal to a processor your brain. The human sensory organs gather their awareness of the external world by perceiving signals. You hear disturbances in the atmosphere carried as sound waves, experience the sensation of heat, react to chemical signals from food through smell, and recognize the shape, color, size, and position of objects by means of the visible light coming from them. Sensations that are not received through direct contact are remotely sensed. The formal definition of remote sensing is: "The acquisition and measurement of data/information on some property(ies) of a phenomenon, object, or material by a recording device not in physical, intimate contact with the feature(s) under surveillance; techniques involve amassing knowledge

2 pertinent to environments by measuring force fields, electromagnetic radiation, or acoustic energy employing cameras, lasers, radio frequency receivers, radar systems, sonar, thermal devices, seismographs, magnetometers, gravimeters, scintillometers, and other instruments". For planetary science, remote sensing seeks to acquire data remotely, to develop information about planets and moons in our solar system. Remote sensing has allowed us to see through the clouds of Venus and through the oceans of Earth. How do remote sensing satellites work? Remote-sensing satellites collect data either actively or passively. For example, radar satellites collect data actively by sending a known signal from the satellite and measuring the portion of the signal that is returned. Passive devices only make measurements, such as the intensity and wavelength of natural light reflected by an object. All objects reflect electromagnetic energy in various wavelengths depending on the object's physical and chemical structure. The important characteristics of remote-sensing systems that measure electromagnetic radiation include spatial resolution, spectral coverage, and temporal frequency. Spatial resolution describes the level of detail, or smallest size of an object, which can be identified. Spectral coverage refers to how many different colors and different parts of the electromagnetic spectrum are measured. Temporal frequency refers to the cycle of coverage or how often data is collected from a particular satellite or spacecraft. Remote sensing systems make trade-offs between spatial resolution, spectral coverage, and temporal frequency. In some cases fine spatial detail is crucial, as with topographic mapping. In other cases, information is needed frequently, but does not require as much detail. For example, a weather instrument may require data several times a day. For other remote sensing instruments, having more measurements in the spectral range may be more important. False Color Images False color images are created using remotely sensed data to make visual representations. These pictures use specific colors to represent elevation, temperature, or other data. Scientists use these images to study the topography, geology, or weather of a planet. A false color image of the surface of Venus created from data taken by the Magellan spacecraft is shown on the next page.

3 Magellan radar data of Venus in false color to emphasize surface topography: (warm colors = highest areas; cool colors = lowest areas). Magellan and the Planet Venus Pioneer Venus image taken in ultraviolet wavelengths shows cloud patterns in the atmosphere The Magellan spacecraft mission was designed to help understand the geological structure of Venus. During its four-year orbital tour from 1990 to 1994, Magellan (named after the Portuguese explorer who first circumnavigated Earth) provided detailed topographic maps and image maps of Venus' surface using radar to penetrate the planet's thick cloud cover. The radar mapped 98 percent of the surface with an image resolution of about 100 meters, and the surface topography was measured with a spatial resolution of 10 kilometers. Additional studies included measurements of the planet's gravitational field using precision radio tracking. At the end of its useful life, Magellan was commanded into a gradual dive into the Venusian atmosphere to obtain information about its properties. It finally burned up on Oct.12, Drawing of Magellan at Venus (not to scale) Galileo image taken through a violet filter and false-colored in yellows shows a featureless atmosphere similar to what our eyes could see.

4 Venus Boxes How do we map the surface of a planet we can t see? The Magellan spacecraft used radar to penetrate the thick clouds that shroud the planet s surface. To map the planet s topography, Magellan carefully measured the time it took for a radar pulse beamed at Venus to bounce back from the planet s surface. If the signal bounced back in a short time, it had reflected off something of high elevation; if the signal took longer to return, it had touched a low area of the surface. The spacecraft continued taking measurements as it orbited the slowly rotating planet until a topographic map of almost the entire surface was made. A similar procedure using sound pulses instead of radar pulses has been used to map the shape of portions of the ocean floor. This activity simulates Magellan s topographic mapping, but uses ruler measurements of the probing device (a coffee stir or cocktail straw) instead of timing a radar pulse. The lid of a shoebox represents the cloud cover of Venus through which your probe must penetrate. You can make the mystery planetary surfaces ahead of time by cutting up styrofoam and gluing pieces inside the shoeboxes to make a landscape with varied topography. You can scrape out impact craters, carve out river channels, and construct mountains or volcanoes. If there is more time in your session you can have students create the mystery boxes and then switch with other teams. You can also tape the graph paper to the lids and prepunch the holes (evenly spaced about 1-inch apart) according to the samples included in this guide. Students will make two topographic maps, one at low resolution and one at higher resolution. If there is not enough time to get to the second map, have one already made to show to the group. Activity Timeframe - 90 minutes Venus Boxes Materials Shoeboxes (one per student) Graph paper 8 1/2 x 11 inches (or larger) Marker Package of cocktail straws or coffee stirs Several sets of crayons with 24 colors Pieces of styrofoam (sheets and/or forms, available at craft supply stores) Scissors and craft knife White craft glue Nails to poke holes in the shoebox lids

5 Preparation 1. Make the mystery planetary surface by cutting up styrofoam and gluing pieces inside the shoeboxes to make a landscape with varied topography. You can scrape out impact craters, carve out river channels, and construct mountains or volcanoes. If you have more time you can have the student teams make the landscapes and exchange boxes with other teams so that what is inside the box will be a mystery when the groups begin mapping. 2. Cut a sheet of graph paper along the grid lines to fit the lid of the shoebox and glue it on top of the lid. Cut two pieces of graph paper to the exact dimensions used for the box lid. (These will become the maps.) Punch holes about every inch depending on the spacing of the grid on your graph paper. The holes should be evenly spaced. Make the holes large enough for the cocktail straws to fit in them. 3. Make a key for mapping the surface in color, using the colors (crayon or pencil) that you have available. For example, the key given in this guide uses warm colors for high, cool colors for medium, and dark colors for low topography. The precise colors don t matter a rainbow effect from high to low is the goal. Introduction You may choose to read an article about the Magellan Spacecraft or the planet Venus to the young group. Share with the group some of the history of remote sensing and the reasons for it. Describe some of the remote sensing instruments used by spacecraft and share some of the false color images (included in this guide) of Venus' surface seen through its clouds. NASA fact sheets and additioinal images can be printed from several of the Websites given in the Related Internet Sites. You can also show a video about the planet Venus. The simulated flyover of Venus, from Magellan data seen in the IMAX film Destiny in Space is excellent (see book and video lists). Timeframe minutes. Remote Sensing Activity Pass out the shoeboxes with the mystery surfaces of regions on the planet Venus. Explain to the group that you cannot see visually through the clouds on Venus. The spacecraft will send radar data back to Earth by bouncing signals off the surface. Then the data processors on Earth can put the data together to form a map of the entire region or planet surface as in the composite image in this guide. Have each two person team get one box of crayons and crayon chart, a straw and a ruler (with centimeters). As they poke the straw through every other hole (and then for the

6 second map, through every hole) they should measure the depth in centimeters and match that to the color chart. Then they should fill in that color on their separate piece of graph paper. The resulting image will be a false color representation of the surface with the gray, pink and reds being the highest and the greens, blues, purple, and black being the lowest areas. If there is not enough time to get to the second mapping activity, have one already made to share with the group. Timeframe - 45 minutes. Procedure 1. Low-resolution map: Begin mapping by inserting the straw probe into the first hole at one corner of the shoebox. Push the straw in gently just until it encounters the surface. Grasp the straw where it enters the box lid and remove it using thumb and forefinger to mark the place. Measure how much of the straw was below the lid with a ruler and note the measurement lightly in pencil on the piece of graph paper. Low numbers will represent the highest elevations, and high numbers represent the lowest elevations. For the low-resolution map, you will measure every other hole in the box lid. Each measurement will correspond to an area about two inches square on the graph paper (this will vary a little depending on what kind of graph paper you are using). The idea is to have each measurement represent a fairly large area. Using the color key, select the right color and color in the entire ~2-inch square with it. Continue measuring every other hole until you have measured and colored the entire surface at low resolution. 2. High-resolution map: Using another piece of graph paper that matches the lid of the box, remap the surface at high resolution by measuring through every hole in the box lid. This time, the area to color in for each hole will be about half as large, or about one square inch (again depending on the kind of graph paper you are using). Using the same technique as before, measure the surface through each hole until you have completely colored in the high-resolution map. 3. Compare the two maps, noting similarities and differences. Make some hypotheses about the kind of surface that you have mapped. Finally, remove the shoebox lids and examine the ground truth. Follow Up Questions 1. Do your maps give a good idea of the actual topography? 2. Are there features that were missed by low resolution mapping that you can see from the high-resolution measurements?

7 Sending Signals Demonstration This simple demonstration shows how data, in this case a visual image, is sent back to Earth is in a series of single lines of data to eventually form a complete picture. Using a slide projector and a slide of the Earth globe (Venus, Jupiter, or another planet) stand approximately 10 feet from the projector lens. Using a yardstick slowly start at the top of the projected globe image and move the yardstick down the image revealing one line of "data" at a time. Now move the yardstick very quickly up and down, it will appear to create a complete image. The planet will appear as a full globe as the images are connected by your brain. This is also how images are sent to your television. Light images are momentarily retained on your retina (called persistence of vision ) an analogy of the imaging process used by computers that reassemble some types of image data sent by spacecraft, satellites and space telescopes. Timeframe - 10 minutes. Recommended Videos Destiny in Space 1994, Sony IMAX pictures Includes a flyover sequence of Venus produced by NASA's Jet Propulsion Laboratory. Magellan - Mapping The Planet Venus $10.00, Grade 7-adult, 10 minutes, Solar System and Beyond - Mapping Venus 40 Minutes, 1994, Timeless Video Inc. "Mission for Mariner," "Magellan: Mapping the Planet Venus," "Collection of Magellan: Venus Radar Mapping Results," and "Magellan: Exploration of Venus." Solar System and Beyond - Venus - The Second Planet 60 Minutes, 1994, Timeless Video Inc. Two programs take a closer look at Venus: "Clouds of Venus" and "Veil of Venus." NASA footage and animation. Books you can borrow from your library Non-fiction Magellan Branley, Franklyn Mansfield. Venus: Magellan Explores Our Twin Planet (A Voyage into Space Book). HarperCollins Children's Books, ISBN:

8 Venus Reddy, Frank and Greg Walz-Chojnacki, Isaac Asimov, Francis Reddy. Earth's Twin: The Planet Venus (Isaac Asimov's New Library of the Universe). Gareth Stevens, ISBN: Vogt, Gregory L. Venus (Gateway Solar System). Millbrook Press, ISBN: X. Fiction Loewen, Nancy. Venus (Greek and Roman Mythology Series). Franklin Watts, Incorporated, ISBN: X. Bradbury, Ray. "The Long Rain" (a short story), from R is for Rocket. Bantam, Related Internet Sites: Magellan and Venus and Remote Sensing NASA's Observatorium Remote Sensing Page Hawaii Space Grant College Remote Sensing Activities Canadian Remote Sensing Tutorial NASA Remote Sensing Tutorial Center for Space Research Remote Sensing

9 JPL Imaging Radar Solar System Windows to the Universe The Nine Planets Views of the Solar System Our Solar System

10 Color Key for Mapping Venus Boxes DEPTH (centimeters) COLOR (Crayola Crayons) ELEVATION RED HIGH SCARLET RED ORANGE YELLOW ORANGE YELLOW YELLOW GREEN GREEN BLUE GREEN BLUE BLUE VIOLET BLACK LOW

11 COLOR KEY FOR MAPPING VENUS BOXES DEPTH (centimeters) COLOR (Crayola Crayons) ELEVATION RED HIGH SCARLET RED ORANGE YELLOW ORANGE YELLOW YELLOW GREEN GREEN BLUE GREEN BLUE BLUE VIOLET BLACK LOW

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