Student Activity
Modeling Satellite Remote Sensing
Build and Operate a Working Model Remote Sensor
Introduction
A covert military operation examines “intel” from images obtained using satellites and cameras on unmanned airplanes. A meteorologist at the National Severe Storm Laboratory in Norman, Oklahoma, analyzes a series of satellite images and other data to predict the path and potential for destruction of a mounting tropical storm in the Atlantic Ocean. A video cameraman records a report by a television journalist at the edge of a growing forest fire that is broadcast live to homes hundreds of miles away. A radiologist uses an x-ray to “see” the broken bone in a young child’s arm. A geologist working for a petroleum company studies a multispectral image from a Landsat satellite to determine the probable presence of subterranean gas and oil in a specific region. What do they all have in common? Remote sensing – using a sensor to detect changes in reflected light at a place other than one we can directly see with our own eyes. That is a loose definition, but the concept is not. Though some remote sensing shown in motion picture stories is fiction, the evolving technology is very real and increasing accessible. During the more than half century since the first launch of an artificial satellite, the body of knowledge about which wavelengths of the electromagnetic spectrum are most reflected by which features of the Earth’s surface and various components of the atmosphere has grown immensely. In this lesson, you will build a simple electronic light sensor that transmits a radio signal when activated by light. The transmitted signal can be received with any FM radio and heard as an audible tone. The quality of the tone varies with the intensity of the light striking the sensor. You will use the sensor to observe and measure the amount of light of various colors when reflected from different surfaces.
Preparation
Attached here are several tutorials to help guide you through the construction, testing and use of your model remote sensor. Your teacher will tell you which ones to use.
· What’s That? – reference sheet with definitions, component descriptions, drawings of components, and component symbols used on schematic diagrams
· Winding the Coil – specific directions for making the inductor by winding your own coil
· Building a Remote Sensor Model – schematic diagram, sensor parts list, construction tips, and bottom view of transistor wire connections
· Sensor Construction – drawings of a breadboard and a completed sensor model to help you visualize the instructions on other guide sheets
· Testing – complete guide to testing and troubleshooting for a properly working sensor model
· Gathering Reflectance Data – procedure for using your remote sensor model to gather reflectance data with the assistance of specialized computer-based probes and data acquisition software
· Data Table – a blank data table for recording your raw data by hand before setting up the spreadsheet
· Determining Relative Reflectance – guidelines for organizing your raw data, setting up the spreadsheet and graphing your data using Excel
· Analyzing Reflectance Data – questions to guide your analysis of the graphs and application of the conclusions to the Your Turn section
· Your Turn – closure activities to extend your understanding by applying the concepts learned to new scenarios
What’s That?
This reference sheet contains definitions, drawings of components, the symbols for the components used in schematic diagrams, and supplemental information about the components and what they do.
Resistor = device to slow electrons in an electronic circuit; measured in Ohms (Ω).
Capacitor = device to store static electric charge in an electronic circuit; measured in Farads (F). Charge is stored and then discharged across the capacitor plates at regular intervals depending on the value of the capacitor. Electrolytic capacitors have an electrolyte between the plates where the charge is stored but then continuously leaked in very small amounts of current between discharges.
Inductor = Inductance is the property of an electric circuit by which a varying current produces a varying magnetic field that induces voltages in the same circuit or in a nearby circuit; measured in henrys (H). You will build your own inductor by winding lacquered wire around a coil form (section of soda straw). Using the safety pin, carefully poke three holes all the way through the straw as indicated. Pass the wire through the first hole to hold the wire in place. Wind the wire around the straw 10 times and pass through the second hole. Leaving about 3 inches of wire extended through the second hole, loop the wire back through the same second hole. Continue winding the wire around the straw in the same direction as before for another 20 turns. Pass the wire through the third hole to hold it in place. The result is a coil of 30 turns with a connecting wire at each end and a connecting wire 1/3 of the way through the coil (called a “center tap”). Use the sand paper to carefully clean the lacquer from about ½ inch of the end of each of the wire leads.
Transistor = A semiconductor device commonly used as an amplifier or an electrically controlled switch. The three leads from the transistor case are the base (B), emitter (E), and collector (C).
Battery = An enclosed storage container for a chemical reaction (dry cell) that supplies a source of electrons to move (current) in an external circuit and the electromotive force (voltage) to move them. Electrons move out of the negative pole and into the positive pole of the battery.
Photoresistor = An electronic component whose resistance decreases with increasing incident light intensity.
Antenna = A transducer designed to transmit or receive radio waves (electromagnetic waves). Antennas convert radio frequency electrical currents into electromagnetic waves and vice versa.
Breadboard = A board with connection points where electronic components can be arranged in a trial circuit with temporary connections. In the breadboard diagram below, each dot is a connection point. Five points are connected together internally as indicated by the lines joining the points in the diagram.
Winding the Coil
Procedure
1. Cut a section of plastic soda straw about 1½” long.
2. Measure ¼” from one end of the straw and poke a hole all the way through both sides of the straw with a straight pin. Do not push the pin into your finger!
3. Measure 3/8” from the first hole and make a second hole in the straw.
4. Measure 3/16” from the second hole and make a third hole in the straw.
5. Magnetic wire is copper wire that has a coating of lacquer instead of vinyl insulation. It is used in making coils that produce a magnetic field when the coils are used as inductors. When working with magnetic wire it is very important that you avoid kinks in the wire and do not scrape the lacquer off the wire.
6. Carefully thread one end of your magnetic wire through the first hole so that the wire goes all the way through the straw. Pull about 3” of wire through the hole for connecting the coil in the circuit later.
7. Hold the 3” wire lead in place and carefully wrap the wire neatly until you have exactly twenty turns around the straw. As you coil the wire, place each wrap immediately next to the previous wrap. Pull the wire tight, but do not deform the straw. Then thread the other end of the wire through the second (middle) hole until the wire goes all the way through the straw. Gently pull the wire snug so the 20 turns of coil stay in place.
8. Double back and thread the end of the wire through the second hole again in the reverse direction leaving about 3” of doubled wire sticking out.
9. Now continue to wrap the wire around the straw until you have exactly 10 more turns of wire.
10. Thread the end of the wire through the third hole and gently pull the wire so that the additional 10 turns stay in place.
11. Cut the excess wire leaving about 3” for connecting the coil in the circuit later.
12. With sand paper, carefully clean the lacquer from the about ½” of the end of each of the three connecting wires. Leave the lacquer on all turns of the coil. Gently twist together the doubled wire from the second hole.
Building a Remote Sensor Model
Purpose
To build a photo sensitive transmitter in order to simulate the identification of Earth’s surface materials by a satellite remote sensor using various frequencies of the electromagnetic spectrum reflected from surface objects
Materials
Transmitter: Q1 NPN transistor, 2N2222 or 2N2222A
I1 Inductor: 30 winds tapped 1/3 of the way from one end
Bat 1.5VDC AA battery in battery holder with leads
C1 4.7mf polarized electrolytic capacitor
R1 47K resistor, carbon film, ¼ watt
R2 Photo resistor
A1 Antenna: 22-guage solid hook up wire, 6-12 inches
FM receiver
Color filters: Monochromatic blue, green, red
Procedure
1. Check to be sure all parts are present and they are the correct parts.
2. Make the inductor: Cut a piece of plastic tubing about 1½ inch long and about 40 inches of magnetic wire. Wind 20 turns of the coil then 10 more turns with a connector protruding from the coil between turn 20 and 21.
3. Carefully place all parts in order following the circuit diagram. Give particular attention to polarity. Determine which transistor lead is the emitter (E), the base (B), and the collector (C) using the diagram below.
4. Do not allow any wire component leads to make connection where no connection is shown in the circuit diagram.
5. Connect each component by soldering, or with a crimp connector, or use a breadboard. If soldering, protect the component from excess heat with a heat sink during soldering.
Sensor Construction
With Breadboard Module
Testing
And Troubleshooting
Procedure
1. Compare the placement and connection of each component to the schematic diagram to verify correct connection.
2. Place the battery in the battery holder.
3. Turn on the FM radio and tune to a relatively silent frequency between stations. Expose the photo resistor to a light source. Listen for clicks on the radio.
4. If you hear the clicks on the radio, skip to Step 7.
5. If you do not hear clicks on the radio, try the following steps:
a. Retune the radio to a different frequency.
b. Check each connection to insure its integrity. Remember, if using a breadboard, the contacts in the breadboard may not be clean. If may help to slip a piece of wire into and out of each contact hole several times to “scrape” the contact clean.
c. Check the connecting ends of all wires including the antenna. Use the sand paper to insure all have been scraped free of any oxide or lacquer coating.
d. Check the battery with a voltmeter to insure it is producing at least 1.5 volts.
e. Check the battery holder is connected correctly in the circuit. Insure the battery contacts on the holder are clean.
f. Check the transistor installation to ensure it is connected correctly. It not, it may be necessary to replace the transistor.
g. Check the coil to insure it is wound correctly and correctly connected in the circuit. Use a continuity tester from the farthest ends to check for breaks in the wire. There should be no breaks even though there is a center connection wire (center tap).
h. Check the capacitor to make sure it is connected correctly. Remember, the capacitor is polarized so connecting it backwards makes a difference.
i. Remove and check the resistor with an Ohm meter. It must be (1) conductive and (2) the correct resistance.
j. Try using a different photoresistor.
6. If clicks are still not heard, repeat Step 5.
7. If clicks are heard, you are ready to experiment with the reflectance of various substances.
Gathering Reflectance Data
Procedure
1. Set up your sensor with the photoresistor in a black plastic tube, if available, to make sure the measured light is reflected from a test surface and not received directly from the light source.
2. Adjust the end of the tube 5 cm from the reflective sample. Place the lamp 7 cm from the source to make sure light does not enter the tube directly from the light source and that the lighting will be consistent. Use white paper for the reflective surface.
3. Set up the microphone, computer interface, and data acquisition software. The software may auto-ID the interface and microphone sensor. In that case, you can use the default screen for data collection. Set the sampling rate to 10,000 samples per second and a collection time of 1.0000 second.
4. Tune a standard FM radio receiver to a frequency with little or no station broadcasting so the clicking pulses can be heard clearly. Place the microphone near the radio speaker.
5. Click Collect to ingest sound data with the computer. When the graph is displayed, each click is apparent as a major peak. The minor peaks are background noise and static.
6. Drag the cursor from an average major peak to the next successive major peak to measure the number of samples between successive pulses. In the menu bar, click Analyze and select Statistics. The number of points between peaks will be counted and listed in a pop-up information box. In Table A on your Data Analysis sheet, record the number of counts (samples) between peaks.
7. Repeat Steps 4-6 using a colored filter in front of the sensor so that the sensor receives only light of that color. Use blue, green, and red filters respectively. Record the counts between peaks for each.
8. Repeat Steps 4-7 changing the reflective surface each time to blue paper, green paper, red paper, and any other surface such as yellow paper, green leaves, or sand. Record the counts between peaks for each.
Data Table
Distance: Reflective surface to photoresistor / cm
Number of Counts Between Pulses
(sampled at 10,000 samples per second)
Reflective / Filter
Substance / None / Blue / Green / Red
White paper
Blue paper
Green paper
Red paper
Unknown:______
Determining Relative Reflectance