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An Introduction to Project ATLAS

The Global Positioning System (GPS)

Using GPS in the Classroom

Experiment 1: The Global Mapping Experiment

Mapping Your Community

Experiment 2: The Community Mapping Experiment

ATLAS Wrap-up and Suggested Activities

ATLAS Worksheets

The Global Mapping Experiment

Classroom time: 40 minutes

Material Covered:

  • Description of the Global Mapping Experiment
  • Outline of Global Mapping Experiment Procedure
  • Choosing the reference mark
  • Determination of the location of the reference mark at the designated time
  • How to use the Garmin GPS Receivers
  • Recording the measurements: The field log sheet
  • Communication of the results to ATLAS colleagues

Description of the Global Mapping Experiment

In this activity, ATLAS investigators will determine their location on Earth and exchange this information with ATLAS colleagues around the world. Using hand-held GPS receivers, ATLAS investigators teamed up by school will determine the latitude and longitude of a reference mark representative of their location, as well as the time of their measurement in Coordinated Universal Time (UTC). These measurements should be made as close as possible to the designated observation time (12 noon in the investigators local time system) on May 6, 1999.

Each school will record these measurements on a field log sheet. The information recorded on the log sheet will then be e-mailed to the Smithsonian Astrophysical Observatory (SAO) at the address atlas@cfa.harvard.edu. SAO will forward the ine-mail to all of the other participants in the experiment. Additional information will also be included in this electronic communication. As this information arrives, the identities and locations of the other schools around the world will be revealed!

Outline of Global Mapping Experiment Procedure

The Global Mapping experiment consists of the following basic steps:

  1. Choose a reference mark.
  2. Determine the location of the reference mark with GPS at the designated time.
  3. Record the measured data (latitude, longitude, and time) on the field log sheet.
  4. E-mail the data to atlas@cfa.harvard.edu, who will distribute the data

These steps are described in detail below.

Choosing the reference mark

There are three important considerations when choosing a suitable reference mark for Project ATLAS: accessibility of the reference mark, stability of the reference mark, and sky visibility from the reference mark.

Because the reference mark constitutes an important component of the ATLAS experiment, including the Community Mapping Experiment, it is essential that it be easily accessible and stationary throughout both ATLAS experiments. Although any physical monument (e.g., flag pole, football goal, the school Principal’s parking space) that is not expected to move during the experiment is acceptable, it will be most convenient if the reference mark is easy to reach.

Since the location of the reference mark is to be determined using radio signals from GPS satellites, obstructions to sky visibility (e.g., buildings, trees) should also be avoided as these may interfere with the hand-held GPS receiver’s ability to see the satellites.

Determining of the location of the reference mark with GPS at the designated time

One of the most important activities in any scientific experiment is the collection of new data.

For the Global Mapping Experiment, ATLAS investigators will collect data, including their geographical coordinates (latitude and longitude) and the time of the measurement in a global time system (described below).

For most global international experiments, coordination and timing is crucial. The Global Mapping Experiment is no exception. For this experiment, ATLAS investigators are to determine their locations on May 6, 1999 (see the ATLAS schedule). Although the time of day is flexible to accommodate various school schedules, all measurements should take place as close as possible to noon local time.

For the pilot phase of Project ATLAS, we will be using GARMIN GPS receivers on loan from the University NAVSTAR Consortium (UNAVCO) Facility in Bolder Colorado, USA. Each unit has a keypad for entering information and a display for reading results. Each GPS receiver also has an internal antenna for receiving signals from the GPS satellites and a small sophisticated computer to analyze all of the GPS signals received by the antenna and to calculate the precise coordinates of the receiver.

The following steps are necessary to determine the location of the reference mark:

  1. Position the receiver over the reference mark.
  2. Turn the GPS receiver on.
  3. Wait for the GPS receiver to acquire data from the GPS satellites.
  4. Record the computed locations and other information on the field log sheets.
  5. Turn the GPS receiver off.

How to use the Garmin GPS Receivers

Please refer to the brief on-line user guide.

To turn the GPS receiver on, press the POWER key on the keypad (a light-bulb cartoon on the GARMIN units). A status or satellite page, showing the receiver’s progress in acquiring satellites, will then appear. This page provides information about the locations of potentially visible satellites, and the strength of the signals that are presently being received by the satellites.

Satellite locations are displayed using concentric circles. The horizon is represented by the outer circle. Overhead is represented by the center point. The inner circle represents an elevation angle halfway between the horizon and the point directly overhead (45° elevation angle).

The satellite page will be in view until the receiver has locked on to at least four satellites, which is required to determine location. Once the receiver has calculated its latitude and longitude, the satellite page will be replaced automatically by the position page.

The position page shows the location of the GPS receiver as well as other useful information such as the direction that you are heading in and your speed. For the Global Mapping Experiment, the GPS receiver should be stationary over the top of the reference mark. Therefore the speed determined by the GPS receiver should be small!

The important information, for this experiment, are the latitude and longitude determined from the satellite signals and the Coordinated Universal Time of the measurement.

The latitude and longitude are located under the heading POSITION. The values are listed as degrees and minutes of degrees. Latitude is the first value listed and will be preceded by either an N for Northern Hemisphere, or an S for Southern Hemisphere. Directly following the latitude is the longitude. The longitude is preceded by either a W for Western Hemisphere, or an E for Eastern Hemisphere.

Although not crucial to the Global Mapping Experiment, you may be interested to know your altitude. This measurement is reported under the ALT heading. The value reported is a measure of the receiver’s distance above sea level in units of meters.

An accurate measure of the time in a global reference system (UTC) is located under the heading TIME. The time reported is the present time at the Greenwich meridian. The value is reported 24 hour format.

Record the required information (see below) onto the Field Log Sheet. These field logs should always be kept in a safe place, as they are your only record of the experiment.

To turn the GPS receiver off, press and hold the POWER key on the keypad (light-bulb) until the display goes blank. The GPS receiver will then shut down. Don’t forget to record your measurements before you turn the receiver off!

Extra Credit: Local Orientation of the GPS Receiver and Satellite Visibility

There is a compass arrow on the top left of the satellite page display showing the north direction. This north arrow is used as a reference for the satellite page display. It points toward the top of the GPS receiver and not necessarily toward the direction of the north pole from where you are! If you know which direction north is (by using a compass, for example), then you can orient the GPS receiver such that this north arrow points in the north direction. The display will then show the directions to the satellites from where you are as follows: mentally draw an arrow with its base at the center of the circles and its head at the number of the GPS satellite on the display screen. This arrow will then point in the direction of the satellite from where you are. Then, using the circles to gage the elevation of the satellite from the horizon, you should be able to get an approximate idea of where in the sky the satellite is located. Understanding where the satellites are located in the sky can help to determine if their signals are being obstructed by terrain, foliage, buildings, etc. Along the bottom of the satellite page is a histogram which shows the strength of the signals that are being received. Little or no signal strength usually indicates that the signal is being obstructed.

Recording the measurements: the field log sheet

Once the students have used the GPS receiver to determine the location of their reference mark, they should be ready to record this information on the field log sheet. The field log sheet (provided below) contains entries for the following information:

  1. Date
  2. Local time
  3. Observation team name
  4. Name of the reference mark
  5. Brief description of the reference mark
  6. Latitude of the reference mark
  7. Longitude of the reference mark
  8. Global time (UTC)
  9. Additional information

Recording data in the field can be more difficult than it may seem. Following are several recommendations for accurately and easily recording data in the field. First, it is helpful to have something flat and solid to write on, such as a clip board. A clip board can also be useful for holding the log sheet in the event of strong winds. Second, you will need something to write with. We recommend using a hard lead pencil. By using a pencil, mistakes can be easily erased. Hard lead pencils are resistant to most temperature conditions and are also resistant to smearing. Third, all information should be recorded while in the field. It is very difficult to remember all of the potentially important details after the fact.

Although the log sheet contains entries for only one measurement of position, it may prove to be a fun exercise to make several determinations of your location. This can be accomplished by repeating the above steps. You won’t always get the exact same results, due to receiver inaccuracies.

Communication of the results to ATLAS colleagues

Once the measurements have been made and recorded, ATLAS investigators will be ready to share their data with colleagues around the globe. You should e-mail the information to the Smithsonian Astrophysical Observatory (e-mail address: atlas@cfa.harvard.edu). You should use the Global Mapping Experiment Sample E-mail as a guide. Your data will then be rerouted to all of the participants in the ATLAS experiment around the world. Likewise, each ATLAS investigator team will receive e-mail from the Smithsonian Astrophysical Observatory containing data from all of the other ATLAS collaborators.

The Global Mapping Experiment Sample E-mail contains entries for essentially the same information that was recorded on the field log sheets. There are additional entries, however, for descriptive information about your investigative team, such as the name of your school, the number of investigators in your team, etc. There is also a place to include a greeting message for your colleagues.

The form should be carefully typed and e-mailed to the Smithsonian Astrophysical Observatory. The e-mail address, again, is atlas@cfa.harvard.edu.

Receiving results from your ATLAS colleagues

At other schools around the world, other ATLAS investigators will e-mail their locations, just as you have. You will receive these e-mails by May 7, 1999. This will reveal for the first time where your ATLAS colleagues are located. Try to find their location on the Globe we provide. You can use the labels to remember their locations.

You will be able to plot their locations on the globe only approximately, because the latitude and longitude lines on the globe are spaced far apart. Still, you will have enough information to determine what continent and perhaps what country and where in their country they are. You should encourage your students to think about these other places. The Web is a great place to learn about other places and people.

The names of the towns and classroom contacts will be made available to you by email…so you and your students can verify the accuracy of your plotting and the accuracy of the data that was received. You and your students may choose to contact one or more of the other schools via written letters or e-mail to find out more about them. Students may be interested in many things about the other students involved in the project. This could lead to some great cultural understanding, and reinforce proper writing skills. You might receive e-mail from other ATLAS participants, asking more about your location, school, and students. You should feel free to answer these e-mails. No particular time is allotted in the ATLAS schedule for these activities; they should be performed as convenient.

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