Information in Radio Waves
Background: Geodesy
Geodesy is the mathematical and scientific study concerned with the determination of Earth’s
exact shape and size along with the precise measurement of points along its surface. The
history of geodesy is extensive and goes almost as far as written history will take us. This is
because humans have long been concerned with the shape the the scope of the lands around
them; whether it be the immediate area around home and family, the distance to the nearest
market, the size and borders of an entire empire, or the desire to know the shape and size of
the entire world. As humanity evolved, so did their understanding of the world around them.
The first pictures of the world as a whole held that it was flat. It wasn’t until the greek civilization
until the notion of a spherical Earth was given any serious thought. At this point, the reasoning
behind Earth being spherical lay in logic based on Earth’s shadow on the moon and on the
angle of the sun over the horizon.
The Greeks were also the first to try their hand at calculating the actual size of Earth with any
reasonable success. Aristotle was the first, reasoning the size of Earth to be around 45,500
miles. Eratosthenes followed up, using sound reasoning and forgivable approximations, with a
much more accurate measurement: about 25,000 miles. He did this by comparing the angle of
the sun at two locations he believed to be directly north/south of each-other on the day of the
summer solstice. Knowing this as well as the distance between the two places allowed him to
calculate both the circumference and radius to remarkably accurate amounts for the times.
Not surprisingly, it was technology that pushed geodesy to new bounds. In the 16th and 17th
centuries, triangulation became the tool to use by surveyors and scientists. Triangulation relied
on the pinpointing of locations based on an angular network of at least 2 other known locations.
And like most all technology and sciences today, geodesy was leaped forward by radio science.
Techniques such as GPS, VLBI, SLR, Satellite Altimetry, and others are the reason we have a
much clearer picture of Earth today.
Information in Radio Waves
Reference:
"GEODESY FOR THE LAYMAN." DEFENSE MAPPING AGENCY TECHNICAL REPORT 80003. Web. 17 July 2014.
<http://www.ngs.noaa.gov/PUBS_LIB/Geodesy4Layman/TR80003A.HTM#ZZ2>.
"Geodesy." NOAA National Ocean Service Education:. Web. 17 July 2014.
<http://oceanservice.noaa.gov/education/kits/geodesy/geo02_histr.html>.
"National Aeronautics and Space Administration." Space Geodesy Project Home. Web. 17 July
2014.
<http://space-geodesy.nasa.gov/>.
Standards:
HS-PS4-1
Use mathematical representations to support a claim regarding relationships
among the frequency, wavelength, and speed of waves traveling in various
media.
HS-ESS2-2
Analyze geoscience data to make the claim that one change to Earth's surface
can create feedbacks that cause changes to other Earth systems.
HS-ESS2-4
Use a model to describe how variations in the flow of energy into and out of
Earth’s systems result in changes in climate.
HS-ESS3-5
Analyze geoscience data and the results from global climate models to make
an evidence-based forecast of the current rate of global or regional climate
change and associated future impacts to Earth systems.
HS-ESS3-6
Use a computational representation to illustrate the relationships among Earth
systems and how those relationships are being modified due to human activity.
Enrichment Opportunities:
GPS simulation http://www.google.com/url?q=http%3A%2F%2Fwww.pbs.org%2Fwgbh%2Fnova%2Flon
gitude%2Fgpsgame.html%2F&sa=D&sntz=1&usg=AFQjCNHo0G_COca_0pOOq_ZNcSP9Jwcmw
Altimetry simulation http://sealevel.jpl.nasa.gov/files/archive/ost/index.html
http://sealevel.jpl.nasa.gov/files/archive/Movie11.html
Altimetry project http://sealevel.jpl.nasa.gov/files/archive/3Dmodel.html
Information in Radio Waves
Unit Breakdown:
This unit is designed to give students a basic understanding of Geodesy and how our Earth’s
size and orientation is established. Included is a powerpoint presentation that covers
Geodesy’s history as well as modern methods of Geodetic measurement. Alongside the
presentation is a “Teacher Notes” section and two assessments, one a pre-assessment the
other post. In addition, two activities have been developed for this unit. One activity has
students do a basic recalculation of Eratosthenes methods using google maps and other
internet sources. The second has students investigate actual GPS data to investigate plate
tectonic movements in Seattle, WA.
1 - Prior to giving the take-home activity “Recreating Eratosthenes’ Experiment,” it is
recommended that the students have been introduced to the methods that he used. There are
many online sources that detail his methods that can be used.
2 - Be sure to personally do the GPS data activity prior to your students.