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.
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.
This chart illustrates how visible colors of light can
represent frequencies of electromagnetic radiation
that the human eye can not “see”.
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.
Today’s Remote Sensing
• Build and calibrate a model of a remote
• 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
• Create a landscape from a set of remote
sensing data (if time permits).
Components for today’s modelComponents for today’s model
of a remote sensing satelliteof a remote sensing satellite
• A barrier strip.
• An LED that is connected to the barrier strip.
• A multimeter that can measure a voltage in
• Wires that connect the multimeter to the a
• A paper cup that serves as a holder for the
The key component of a model of a
remote sensing satellite is a
light emitting diode (LED).
LEDs can emitLEDs can emit andand detect light.detect light.
LEDs are usually used to
emit light of a specific
LEDs can also transform
light into an electrical
An electric meter can detect the voltageAn electric meter can detect the voltage
produced by the LED that is used to detect light.produced by the LED that is used to detect light.
The voltage depends on the color of light detectedThe voltage depends on the color of light detected
by the LED and the intensity of the light.by the LED and the intensity of the light.
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
• 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
Calibrating a Model of a Remote Sensing SatelliteCalibrating 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
• Continue the process of obtaining signals for paper of different
• Conduct several trials of obtaining signals for different colors of
A Few Definitions of Voltage
Voltage is a measure of the difference of
electric potential between two points in an
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
• 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
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
• 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
A few questions.
• How was your false color image of a landscape
similar to a false color image of precipitation used in
• 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
• What are some ways that students could use the
model of a remote sensing satellite to design an