GPS Geo-Caching, Mapping and Physical Modeling
Lesson Plan
GPS Geo-Caching, Mapping and Physical Modeling
Author:
Byron Lahey
Grade Level:
7 (appropriate for broader range with level appropriate adjustments)
Standards
Strand 2: History and Nature of Science
Concept 1: History of Science as a Human Endeavor
PO 2. Describe how a major milestone in science or technology has revolutionized the
thinking of the time (e.g., global positioning system, telescopes, seismographs,
photography).
PO 3. Analyze the impact of a major scientific development occurring within the past
decade.
PO 4. Analyze the use of technology in science-related careers.
Strand 3: Science in Personal and Social Perspectives
Concept 1: Changes in Environments, PO 1, PO 2. (Discuss use of GPS technology
[Radio Occulation] for atmospheric analysis.)
Strand 4: Life Science
Concept 3: Populations of Organisms in an Ecosystem (Discuss use of GPS for
tracking wild life.)
Strand 6: Earth and Space Science
Concept 1: Structure of the Earth, PO 3. (Discuss use of GPS for study of
earthquake and volcanic activity.)
Concept 2: Earth’s Processes and Systems, PO 3, PO 6. (Discuss use of GPS for
study of earthquake and volcanic activity.)
Grand Challenge for Engineering
Engineer the tools of scientific discovery
Overview
This lesson introduces GPS technology through a series of hands on activities. These
activities are scaffolded by group discussions and a presentation. The first activity is
a geo-caching exercise that requires a variety of navigation and problem solving
skills. Each geo-cache presents a question or fact about GPS technology and its uses.
The second activity uses Google Maps to reinforce the lessons learned in the geocaching activity and to solidify the students understanding of the latitude-longitude
coordinate system. The final activity requires students to physically model the
relationship of GPS receivers and satellites in an attempt to answer the question of
how many satellites a receiver must connect with to fix its 3D position.
This lesson is designed for two full days but could easily be expanded if more time
was available for deeper exploration of any of the topics introduced.
Day one is primarily dedicated to the geo-caching activity.
Day two is split between the online mapping explorations, a brief Power Point
presentation and a physical modeling activity.
General Questions and Concepts
Student’s preconceptions of GPS technology and its applications should be explored
and taken into consideration. Most students will have direct or indirect (via
advertising for example) experience or knowledge about GPS but many will only
think about GPS as a navigation tool. Reminding students that smart phones use GPS
may dramatically expand their perception of the uses of GPS as they consider apps
that use “location services”.
Introducing the Grand Challenges for Engineering and the specific challenge of
“engineering the tools of scientific discovery” is a powerful way of helping students
consider GPS technology as something more than a way to drive around an
unknown city.
The geo-caching activity as it is structured in this lesson requires students to
exercise a skill that was historically valuable but currently far less frequently called
on: orienting oneself to a specific direction. Asking students what direction is
northeast will likely result in a delayed social negotiation that will ultimately resolve
in roughly the right direction, but also demonstrate the weakness of this
unexercised skill. Asking students whether the magnitude of longitude coordinates
(disregarding the negative sign if in the western hemisphere) will increase or
decrease if one travels east will likely result in blank stares. The mapping and geocaching activities should improve understanding of the question at the least and
result in confident answers at best.
Describing a few of the technical characteristics of GPS can really spark students’
imagination. For example, GPS satellites orbit at an altitude of around 11,000 miles
and broadcast their signal at 50 watts or less. Telling students, after they have
successfully started seeing live position data on their receiver, to “Imagine standing
on a mountain in Los Angeles. Now look off in the distance for that 50-watt light
bulb on top of the empire state building in New York City. The satellites that your
receiver is getting data from are about 4 times that far away.” The students might be
prompted to consider what other things that are invisible to us can be perceived by
scientific tools.
Preparation:
Initial staging of the geo-caches requires some planning and coordination. Typical
geo-caches are extremely well concealed in their environment so as to minimize the
chance of them being accidentally discovered by a casual observers. This degree of
concealment would dramatically increase the time required for this lesson. One
must find a balance that requires students to calculate and navigate to the correct
location (not making the caches to easy to spot from a distance), while making it
easy enough for them to be located once the students are in approximately the
correct location. This presents a secondary challenge: the caches may be spotted by
other students not participating in the class, making the caches vulnerable to
displacement or destruction. Hiding the caches in a location that minimizes this
exposure and/or communicating with other faculty and staff is essential.
The geo-caching activity is structured as follows:
First Cache:
The location of the first geo-cache for each group of students (group size will be
determined by the number of available GPS receivers and class size) is stored as a
waypoint in the GPS receiver. Each receiver should be labeled for the corresponding
group and must be independently programmed with this unique location. Students
navigate to this first cache by simply following the directional and distance
information presented by the receiver. This first challenge is intended to get the
students acquainted with the basic operation of the receivers. Prior to sending the
students out to search they should be instructed on proper care and use of the
receivers, including showing them how to access and use the compass mode of the
receiver (most GPS receivers will have such a mode). Locating the first geo-cache
should be as simple as following the arrows and watching the estimated distance
from the pre-recorded waypoint get smaller. For most students this will be very
simple and will reinforce any prior experiences with GPS navigation devices. It
should also provide a hint at how to find the second geo-cache.
Second Cache:
The first geo-cache will contain a fact or question about GPS technology. Students
should copy this information and attempt to answer the question. They should also
produce a written reflection on any challenges or discoveries they made while
finding their cache. The first cache will also contain directions to find the next cache.
In this case the instructions will describe the location as some distance and
direction (a vector) from the first cache location. This requires students to orient
themselves and figure out how far to travel in that direction. Maps may be provided
to assist with this, but are not required. The simplest and most accurate way to
solve this challenge is to use the compass mode of the GPS receiver, a map or
existing knowledge of directions to orient oneself correctly, and then use the first
geo-cache waypoint as a reference. Students should recall that when they moved
towards the first cache the distance decreased as they got closer and realize that the
distance will increase as they walk away from this location. When the distance from
the first cache matches the prescribed distance they should be very close.
Third Cache:
The location of the third geo-cache will be presented in latitude and longitude
coordinates only. No waypoint will be recorded for this location. This requires the
students to study the coordinates and determine which way to travel to find this
location. The intent in this case is to get the students thinking about what those
numbers really mean and at a minimum figure out what direction they need to go to
make the numbers increase or decrease in magnitude. An additional lesson
embedded in this activity is an introduction of the concepts of the scale and
resolution as it relates to the GPS system.
An important consideration with this activity is the possibility that some caches
may, for any number of reasons, not be found. This is significant because of the
sequential nature of the system: each cache includes directions to the next. Some
contingency plan needs to be arranged to insure that some students to not get stuck
by not finding their first cache. This can be accomplished by having backup copies of
the locations and enclosed cache messages in the field (to be distributed as needed)
or by giving the teams sealed envelopes with this information to be opened if
needed at a set time point. Numerous GPS visualization tools are available to
produce a map of the geo-caches. One is illustrated in the accompanying Power
Point presentation. A sample spreadsheet that can be used with this visualization
tool is also provided.
A final rendezvous point is preprogrammed in each GPS device and should be used
by each team at a pre-established time to bring all the students back together for a
discussion. The questions and facts they found on the activity should provide a
strong foundation for this discussion. Many of the facts will help lead to answers for
the questions but others can be assigned as homework or future research. This is a
good opportunity to relate GPS technology to prior or upcoming class lessons.
Examples include earthquake and volcanic activity, migration patterns of animals,
weather and global climate changes, etc.
Mapping Activity/Presentation
The mapping activities are detailed in the included Power Point presentation.
Physical Modeling of GPS Satellites-Receivers
This activity (also introduced in the Power Point presentation) challenges the
students to answer the question: How many satellites must a GPS receiver connect
with to establish its 3D postion?
The students are separated into groups of four but are told that they may combine
with another group if the decide they need more people to complete their model.
Student’s bodies (specifically their one of their hands) represent either a satellite or
a receiver. A length of rope or a wood dowel rod represents the connection between
the satellite and receiver. Students are told that the only information that a single
satellite connection communicates is the distance of that satellite from the receiver.
The instructor and a volunteer should demonstrate that a single satellite defines a
spherical range of possible locations for the receiver.
It should be emphasized that this model represents a static snapshot of the GPS
system at a fixed moment in time. This simplified view does not demonstrate the
orbital motion of the satellites (though if time allowed and the students were
sufficiently advanced, this feature could be modeled). For this exercise, the students
representing satellites should be instructed to keep their hand (the satellite) in a
fixed location. The receiver (another student’s hand) can move only with the
freedom allowed while maintaining the fixed distance to the current number of
satellites. The students should discover that adding a second satellite limits the
motion of the receiver to a circle and that a third satellite reduces the possible
location to two points. A fourth satellite fixes the location to a single point. At the
point of adding the third satellite many students will conclude that this fixes the
receiver at a single location. It may take some prompting with additional questions
or a physical demonstration to convince them that this is not the case. Pointing out
that spacecraft can use GPS may help them recognize this. They may argue
(correctly in principle) that if the receiver is known to be on the ground, that the
roughly spherical shape of the earth provides the final constraint for the system.
They should be congratulated for this logical thinking but can be told that the forth
satellite is still mathematically required because it allows for a final time
synchronization between the receiver and the satellite that is not possible with only
three satellites. A thoughtful student might observe that even with a fourth satellite,
the receiver could still be in two locations. However it can be pointed out that this
would only be possible if the satellites were in a perfectly symmetrical
configuration.
The choice of using string/rope or a rigid material such as wood dowel rods is
somewhat of a personal preference but may be informed by a few considerations.
Sting or rope may be less expensive and is easily acquired and stored. Its flexibility
has pros and cons. The disadvantage of the flexibility is that it may take more
discipline to maintain the tension that defines a fixed distance. The advantage is that
it is easier to explore the two locations provided by three satellites. Wood dowel
rods have the advantage of more easily establishing a fixed distance.
After testing this exercise in one class day with five classes of students using rope
for four classes and dowel rods for the fifth, I would recommend trying a variation
on this model. In this variation the student’s hand as a receiver would be replaced
with a weight that can be suspended from strings. This might make it easier to
demonstrate the full range of the receiver positions by allowing the weight to be
swung around. With two satellites this would be like a jump rope. The third satellite
would clearly fix a position with the help of gravity. A helium balloon with a
removable weight would function exceptionally well as a receiver to demonstrate
the two possible positions with three satellites.