Remote Sensing Transforming electromagnetic radiation into an electrical signal April 4, 2009

Meteorologists use radar to study the reflection of radio waves from raindrops, sleet, and snowflakes to determine rates and types of precipitation. http://science.nasa.gov/headlines/y2007/02mar_rainandsnow.htm

Different amounts of reflected radio waves are then transformed into visible colors of light. The result is a “false color” image of the rates and types of precipitation. http://www.google.com/webhp?hl=en

This chart illustrates how visible colors of light can represent frequencies of electromagnetic radiation that the human eye can not “see”. http://chandra.harvard.edu/photo/false_color.html

Radar on satellites is also used to detect changes in the way that sea ice scatters radio waves. Scatter data is used to produce a false color image that indicates different ages the age of sea ice. http://eosweb.larc.nasa.gov/HPDOCS/misr/misr_html/beaufort_sea_ice.html

Today’s Remote Sensing Design Challenges Build and calibrate a model of a remote sensing satellite. Create a model of a landscape using different paper of different colors. Use your model of a satellite to analyze light reflected or emitted from the landscape. Create a “false color” image of the model of a landscape. Create a landscape from a set of remote sensing data (if time permits).

Components for today’s model of a remote sensing satellite A barrier strip. An LED that is connected to the barrier strip. A multimeter that can measure a voltage in millivolts. Wires that connect the multimeter to the a barrier strip. A paper cup that serves as a holder for the LED.

The key component of a model of a remote sensing satellite is a light emitting diode (LED). http://electronics.howstuffworks.com/led.htm

LEDs can emit and detect light. LEDs are usually used to emit light of a specific wavelength. LEDs can also transform light into an electrical signal. Discuss the motor/generator analogy

An electric meter can detect the voltage produced by the LED that is used to detect light. The voltage depends on the color of light detected by the LED and the intensity of the light. http://mvh.sr.unh.edu/mvhinvestigations/light_investigations.htm

Alligator clips of wires that connect an LED to a multimeter usually do not make a good connection to the thin lead wires of an LED. A Barrier Strip can be used as a link between the LED and the multimeter. An LED can be connected to two terminals on one side of a barrier strip. The alligator clip ends of connecting wires can then be connected to two terminals on the other side of the barrier strip.

Assemble a model remote sensor. Curl the ends of the two LED wires so they can be attached to terminals on one side of the barrier strip. BE CAREFUL ! The ends of the wires of the LED are sharp. Connect the LED to two terminals on one side of the barrier strip. Connect the alligator clips of two connecting wires to terminals on the other side of the barrier strip. Use a screwdriver to carefully put a hole in the center of the bottom of a paper cup. The hole needs to be big enough to easily insert and remove the LED. Insert the LED into the hold in the bottom of the paper cup. Secure the barrier strip with masking tape. Connect the banana plug of one of the connecting wires to the COM terminal of the multimeter. Connect the banana plug of the other wire to the V/Ω terminal of the multimeter. Choose a multimeter setting that will measure up to 200 millivolts.

Calibrating a Model of a Remote Sensing Satellite Create a stack of paper of different colors with a white sheets of paper on top followed below by red, orange, yellow, green, blue, and black sheets of paper. Move the remote sensing satellite assembly to the stack of paper so that the open mouth of the paper cup is over the center of the top sheet of paper. Turn on the multimeter. Adjust distance between the mouth of the paper cup and the top sheet of paper so that a stable millivolts signal is obtained. Record the signal for the sheets of white paper. Remove the sheets of white paper to obtain the signal for red paper. Continue the process of obtaining signals for paper of different colors Conduct several trials of obtaining signals for different colors of paper.

A Few Definitions of Voltage Voltage is a measure of the difference of electric potential between two points in an electric circuit. Voltage can also be described as the amount of energy that is transformed (Joules of energy per coulomb of charge). In this activity, the LED is transforming visible light into electrical energy

Create a Landscape Review your calibration data. Choose three different colors of paper that produced distinctly different LED voltage signals. Decide what type of landscape variations you want to create. Use those three colors of paper to create a landscape.

How will you collect data so that the data can then be used to draw an image of the landscape?

Create a False Color Image Choose a separate false color marker for each color of paper used to construct the model of a landscape. Review data that you collected as your remote sensor passed over the landscape. Use that data to create a “false color” image of the landscape.

Analyze Another Group’s Data (If time permits) Obtain a set of landscape data from another group and attempt to construct the landscape that they analyzed. Use three different colors of paper to construct the landscape that the other group analyzed. Compare the landscape that you constructed with the false color image the other group constructed.

A few questions. How was your false color image of a landscape similar to a false color image of precipitation used in weather reports? How was your false color image of a landscape different from a false color image of precipitation? How could this activity be integrated into your STEM curriculum? What are some ways that students could use the model of a remote sensing satellite to design an investigation.