Infrared Remote Sensing: Using a Remote Sensor to Produce an Image

Objectives:

Grade Level: 4-6

Time Duration: two 50-minute class periods

Skills: measurements, reading a thermometer, averaging

Subjects: geography, math, science, art

Framework: energy, scale and structure, systems and interactions

Vocabulary:
remote sensing, vertical, false color, true color, surface, topography, range, data collection

Materials:

[WARNING! - Students should use alcohol thermometers, not mercury thermometers. Also, students should be cautioned that thermometers can break and sharp glass can cause cuts.]

Description:
Have you ever wanted to be able to perceive things others could not? Or felt something magical when given a way to see something you are not normally able to see? That is what remote sensing does for us. Each person is equipped with remote sensors. We can see, hear, or sense the temperature of something that we are not touching. Any device or sense that perceives an object without contact is a remote sensor. Remote sensing instruments collect data that we do not have the faculties to sense. They perceive, measure and record, energy in the electromagnetic spectrum. Numbers and, in the case or remotely sensed imagery (RSI), colors are assigned to represent frequencies in the range perceived by the sensor.

Many remote sensors are sensitive to energy reflected in the infrared region of the spectrum. Other instruments are sensitive to the visible and ultraviolet regions of the spectrum. When sunlight strikes an object, part of the energy is absorbed and other parts are reflected in wavelengths of varying lengths. Waves reflected in the visible light band our eyes perceive as colors.

The waves that have a higher energy and are shorter than what we can see are ultraviolet (and beyond) wavelengths. (See the diagram of the electromagnetic spectrum in the lesson.)

The sensors used in remote sensing often operate at great distances from the subject being measured. When we sense at close range the temperature of an object, we are perceiving the temperature of the wavelengths that the object is emitting. Remote sensing instruments that are sensitive to infrared wavelengths detect these frequencies that the object reflects or did not absorb.

An object that is cooler than surrounding objects is not emitting as much infrared radiation (heat) as those other objects. For example, we perceive forests as places that are cooler than areas that are developed and paved with asphalt. A remote sensing instrument, registers less heat from the forest than it does from the nearby road or suburb. Therefore it records a lower temperature over a forest than over a downtown.

Once data are collected by the sensor, colors are assigned to the bands along the range of wavelengths recorded. From this, digital images are produced. Since the color of the objects is not true to what we are used to seeing, they are called false-color images.. Any color can be assigned to a given frequency to enhance specific features if desired.

This activity is done best on sunny days during the heat of the day. Return with your students to the sight of the activity entitled, Analog vs. Digital and use thermometers to record the temperature of the ground in the center of each square in the grid. Create a color guide coded to specific temperature ranges to color the grid thereby creating a remotely sensed image.

Procedure:

  1. Look at the aerial and satellite remotely sensed photographs from Project ADEPT . The LANDSAT imagery shows how remote sensing provides information different from images taken with visible light.

    Dambos are areas along riverbanks that absorb and hold stagnant water after heavy rains. Disease carrying mosquitoes breed in this stagnant water. The RSI shows in red the location of flooded dambos. (It may be noted that certain radar systems enhance the capability of remote sensing by looking through clouds, something that is not possible to do with aerial photography.)

    Discuss with the students the background of the photos. What does the aerial photo show us? What features can you see in the remotely sensed photo? When would we need to use each type of image?

  2. Ask students what remote sensor they used to collect data for the activities in Analog vs. Digital (answer: their eyes). Today they will use another remote sensor, a thermometer, which measures in a part of the spectrum that humans can not see, in the infrared or what humans perceive as the heat or thermal part of the spectrum.

  3. Move the class to the data collection sight for the exercise Analog vs. Digital . Each student should have a pencil and paper, and a thermometer. Someone should bring the calibrated string, bell, and timer. Place the grid over the exact same area as in Analog vs. Digital . Place each student in the exact center of each square or next to any landmark in the square. Have each student hold the thermometer so that it is in the center of the square and at 90 degrees (perpendicular to the ground. Each thermometer should face the same direction in relation to the sun so that the difference in data reflects landscape temperature rather than data collection technique.

    Be sure to control the measurements by considering each of the following:

    • Distance of the thermometer from object to be sensed.
    • Direction of the thermometer in relation to the sun.
    • Time when thermometers are read.
    • Placement of students in the grid.

  4. Wait three minutes and ring the bell. At the sound of the bell, all students should read their thermometers and record the temperature shown on paper. (The temperature should be recorded with the best precision possible with the thermometers, perhaps to a tenth of a degree.) Repeat this procedure two to four times at three minute intervals.

  5. Collect the materials and return to the classroom. Students can now average their data or chose a specific, consistent collection to represent each square of the grid. List or graph the data on the board to get a range. Calibrate (normalize) the range, then assign colors to each zone. When assigning colors to each zone, you can use cool colors for lower temperatures and warm colors for higher temperatures. Refer to the sample of a color scheme in the figure below.

    Any color code can be used, but remember, the purpose of this exercise is for students to see that objects have properties that can be represented visually.

  6. Students can now determine the color of their own square then use that color to color in the square on the large grid. Each student can reduce and replicate the large grid by coloring corresponding squares on their 20 x 20 cm grid sheets.

  7. Compare today's image with those created from the Analog vs. Digital activity. Can you see any common features? Look at your homemade RSI. Is it an analog or a digital image? What can you see? What does the image tell you? How can you use this information? Can you tell which areas have biotic or abiotic features in them? What is the scale of our large remotely sensed image? What is the scale of your reduced RSI? What is the resolution of each image? How can we create an image with greater resolution?

  8. Discuss the relationship between the colors and the electromagnetic spectrum. What does an RSI in the infrared tell you that other images do not? What can you tell that you could not tell before?

Assessment:
You work for a county rescue agency. It has rained heavily enough during the last twenty-four hours to cause extensive flooding. the telephone lines are down in fifty percent of the county. Your agency needs information on the locations where the flooding has reached levels that are dangerous for the citizens. How can an RSI help you? Can an infrared or a visible light image be of the most help?

Extensions:

  1. Repeat this activity at another time of the day or year. Analyze the difference between the two or more data sets.

  2. Take a walk around the campus or town and take temperature readings at various sites. Compare the readings with the school-yard site and discuss.

  3. Change the color code by changing the relationship between colors (monochromatic, analogous, complimentary) or the calibration within the range (20-degree range divided by 4 degrees per zone gives 5 colors to use; 20-degree range divided by 2 degrees per zone gives 10 colors to use.) Have students fill in a new grid creating a different image.

  4. Create a coordinate grid by using the degrees of temperature to be the values within the image and the number of the degrees to be the corresponding integers. Discuss with your students if and how this is different than assigning number to the values within the image that they have created.



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