Week Seven: The Science behind Electromagnetic Waves, or How in the World Does the Radio Work?

You're driving in your car, and you turn on your radio.  Suddenly, Bruno Mars is belting out "Uptown Funk" while you dance along.  In this day and age, no one really questions if or how a radio emits the specific sounds that make up our most beloved Top 40 songs or favorite NPR talk shows, but when you think about it, the concept of radio waves, or any type of electromagnetic waves for that matter, are quite an abstract concept to think of.  Anything we see or hear relies on these strange waves that almost everyone is so familiar with but knows nothing about.  Remote sensing relies on these electromagnetic waves.  Actually, organs like our ears are really remote sensing tools that allow us to pick up sound waves.  This week, we delved into how electromagnetic waves work and allow remote sensing to be possible.

First, what is electromagnetic energy?  Also known as electromagnetic radiation, this is energy emitted in the form of waves that is released from anything over 0° Kelvin, or -273.15° C.  The sun is the main source of electromagnetic energy, but virtually everything around us emits some type of electromagnetic energy, including ourselves.  All the different types of electromagnetic energy lie on the electromagnetic spectrum, this includes the different waves we perceive, such as color and radio waves, as well as the "invisible" waves such as infrared and X-rays.

  

Source: http://butane.chem.uiuc.edu/pshapley/GenChem2/A3/3.html

 

So there are all these waves flying around us willy-nilly? No, there are rules to how these different waves act in nature.  First, each type of wave has a different period, or time it takes to go through one wave revolution (think of following the line up a hill and down a valley; that's one period).  These wavelengths are measured in nanometers.  The amount of nanometers a period tells us the frequency of a wave.  The shorter the wave, the higher the frequency.  The amplitude, or height of a wave is another defining characteristic that allows us to differentiate between types of waves. Using Planck's Radiation Law, we can find the wavelength (basically what kind of wave) emitted by a blackbody, or anything that absorbs all light that hits it then re-emits energy back (Photovoltaic Education Network).  I'm trying to keep this entry simple, so I won't explain the equation that let's us figure this out, but I'll still show it:

 

Source: http://csep10.phys.utk.edu/astr162/lect/light/radiation.html

Basically, Planck's Radiation Law (the above equation) proves that for every fixed temperature, there is a fixed wavelength (Radiation Laws).  Some other related laws that help to explain the behavior of electromagnetic radiation are the Stefan-Boltzman Law and Wein's Displacement Law.  The Stefan-Boltzman Law tells us the total energy emitted from a blackbody (Radiation Laws).  From Wein's Displacement Law, we learn that temperature and peak wavelength are proportional, because their product remains constant.  This allows us to find out the temperature of different blackbodies based on their wavelength (HyperPhysics).  

 

Source: http://csep10.phys.utk.edu/astr162/lect/light/radiation.html

 

Using all these laws, we can determine the behavior of different wavelengths across the electromagnetic spectrum.  This is important in remote sensing, because we are able to use this information to manipulate different waves.  One basic example of this manipulation is in FM and AM radio.  FM stands for "frequency manipulation" and AM stands for "amplitude manipulation."  This allows us to make certain sounds come over different channels on the radio.  Thanks to the science of electromagnetic waves, we are able to pinpoint and collect different types of data from satellites. So next time you're jamming out in your car, take a second to think about the amazing science we often take for granted in electromagnetic radiation.

Bibliography:

HyperPhysics. Ed. Carl R. Nave. Georgia State University, 2012. Web. 26 Feb. 2015. <http://hyperphysics.phy-astr.gsu.edu/hbase/wien.html>. 

Photovoltaic Education Network. Ed. Stuart Bowden and Christiana Honsberg. Arizona State University. Web. <http://pveducation.org/pvcdrom/properties-of-sunlight/blackbody-radiation>. 

"Radiation Laws." Astronomy 162. University of Tennessee, Knoxville. Web. <http://csep10.phys.utk.edu/astr162/lect/light/radiation.html>. 

        

Week Six: A Bird's Eye View

From satellites, we are able to gain visual information impossible to see with the human eye.  For example, satellites have the capability to capture thermal or ultraviolet images.  Although these parts of the light spectrum are invisible to humans, different animals can perceive them just as clearly as we see color.  In order to better understand the light spectrum beyond what we can see, this week we studied the eyes of birds, an animal that can sense ultraviolet light.  Now if you're like me, the only information you remember about how eyesight works you learned before high school.  Prior to this week in class I basically remembered the basic eye parts like the iris, cornea, and optic nerve, and that at some point the image we see is flipped upside down.  Other than that I was in the dark, so I'll just assume you are too and give a little crash-course on vision.  First, when we see something with our eyes, we are sensing parts of the light spectrum.  On the light spectrum, there are various waves of different lengths.  For each different type of wavelength, there is a coordinating photoreceptor.  In humans, we have rod and cone photoreceptors that pick up certain waves, which allow us to sense different colors (Fairchild, 9).  We don’t have all the types of photoreceptors to see every part of the light spectrum, though, which is why we can’t see in the dark or sense ultraviolet or heat waves.  

 Way back in history, when mammals started to evolve, we lost two of our four cone pigments.  Later on humans did evolve back to having three cone pigments (Goldsmith, 71).  While humans only have 3 types of cones, birds on the other hand use four cone pigments, allowing them to sense in ultraviolet.  This creates a whole different world to sense visually.  

 

The difference of a flower between what we see (left) and what birds see in ultraviolet (right)

Source: http://www.lifepixel.com/galleries/uv-ultraviolet-photography-gallery 

 While the ozone layer filters out much of the ultraviolet radiation coming to Earth, ultraviolet astronomy can only be conducted from space, which makes satellites integral to this type of research (http://www.scienceclarified.com/Ti-Vi/Ultraviolet-Astronomy.html).  With the use of satellites, we have the opportunity to broaden our view of the world beyond what we can see with our sense of vision and truly see from a bird’s perspective.

Week Five: The Science of Satellites

This week in class we focused on satellites and how exactly they stay in orbit up in space. For most people, me included, space is a very abstract idea. We know that it's there, but we don't really understand how it works. Space is devoid of a lot of things integral to our daily lives like sound and gravity, so it seems more like fiction than reality. In order to grasp how satellites "fly" through space, we first had to learn how things fly on Earth. The adaptation of flight has happened separately four times with birds, bats, insects, and pterosaurs. Some factors that affect flying in winged animals is weight and air resistance. Both these things have no effect on the things orbiting in space, though, since there is no drag or weight in the vacuum outside our atmosphere. There is still gravity acting in space, but it is not as strong as when we are on Earth. In the Manuel “The Physics of Space Security” I learned that when satellites travel through space, Earth is constantly pulling it toward its center. This brought up my initial question of why doesn't the satellite just fall back to the earth then? Well, as the satellite continually falls, the earth is constantly curving away from it, creating a path for the satellite that remains parallel to the earth’s surface while in orbit. I was still a little fuzzy on this concept at first, but then I learned one visual that really helped me out. Think of if you were to spin a string with a ball tied to the end in the air. The ball moves in a circular “orbit” around your hand. This is basically the same thing going on with satellites, just the string is invisible. The “string” in space is Earth’s pull of gravity on the satellite. Just as if the ball would fly off if it broke from the string, a satellite would zoom off into space if Earth’s gravity was not holding it back. Thus equal and opposite forces of the earth’s gravity and the satellite’s inertia help to create the orbital path a satellite follows.
Satellites have many different uses in the world today, and I found a few different types through some further research:

Geostationary Operational Environmental Satellites, or GOES are used for collecting data on weather. Launched in April of 2010, GOES 13 is the current GOES East, responsible for remote sensing of the eastern United States.
                                        

An infrared image of the eastern United States taken by GOES 13

http://www.goes.noaa.gov/goes-e.html

Global positioning satellites, or GPS circle the earth at a medium orbit, completing revolutions twice daily. There are 27 operational GPS satellites currently.  Together, they create a net of satellites that can track where you are and give you directions to a place you want to be.  GPS was originally used only for the military, but in recent years became open to public use. The Block IIF satellite launched in 2010 and is planned to remain functional until 2025. 

  

The Block IIF GPS

http://www.gps.gov/systems/gps/space/ 

 

The Terra and Aqua satellites are NASA satellites dedicated to data collection concerning various environmental systems.  For example, with Moderate Resolution Imaging Spectroradiometer, MODIS for short, the satellites are able to record “net product productivity,” or the amount of carbon turned into other matter by plant life.  This tool also collects data on fires and their effects. From the collected data, scientists are able to learn more about the carbon cycle and how it is changing in the present day.

 

A picture of Earth captured from the Terra satellite

http://www.spacetoday.org/Satellites/TerraAqua/TerraStory.html 

 Sources:

Reibeek, Holli. "The Carbon Cycle." Earth Observatory. Ed. Michael Carlowicz. NASA, 16 June 2011.

http://www.goes.noaa.gov/goes-e.html

http://www.gps.gov/systems/gps/space/

http://www.spacetoday.org/Satellites/TerraAqua/TerraStory.html