Wave Properties and MOSAIC

1. Wave Properties and MOSAIC A Physics MOSAIC MIT Haystack Observatory RET Revised 2011 Background Image from Wikipedia, Roger McLassus, Creative Commons

2. Reflection • When a wave encounters a boundary, it will be at least partially reflected off this boundary. • In sound waves, this reflection results in an echo. This is used in • Echolocation • Sonar • Ultrasound imaging Public Domain Public Domain Image from SKMay

3. Reflection off Fixed, Free Boundaries Animation courtesy of Dr. Dan Russell, Kettering University When a wave reflects off a fixed boundary, it becomes inverted. When a wave reflects off a free boundary, it remains upright.

4. Refraction • When a wave encounters a boundary where it is partially transmitted, the wave speed and wavelength of the wave will change due to the change in medium, and, as a result, the direction of the wave will change. Image from yggmcgill, Wikipedia, Creative Commons

5. Refraction Wave Fronts Animation from Oleg Alexandrov, Wikipedia, Public Domain

6. Wave-Only Properties • Both reflection and refraction could be understood from the perspective of both particles and waves, as particles can both reflect and bend when passing from one medium to another. • Interference, however, cannot be understood from the perspective of particles. Two particles cannot occupy the same place at the same time. • Diffraction, too, can only be understood as a wave property. Image from Wikipedia, Public Domain

7. de Broglie concluded in 1924 that “any moving particle or object had an associated wave” (de Broglie hypothesis). This has become accepted as the principle of wave-particle duality. All particles have wave properties, but the wavelength depends on the particle’s momentum. Specifically, The scale at which one observes wave behavior is comparable to the wavelength of the particle, and, since h is a small number ( 6.626 x 10-34), only very small particles have noticeable wave properties. Waves vs. Particles Image from Public Domain

8. Sharing a Medium • What happens when two waves pass through the same physical space? ?

9. Superposition Principle • When two (or more) waves pass through the same medium at the same time, the resultant displacement of the medium is the superposition of the displacements from each wave. • The velocity of each wave is unaffected (in direction or speed). !

10. Constructive and Destructive Interference • Constructive Interference: Occurs when two waves pass through the same physical space and result in a greater displacement than the original waves. • Destructive Interference: Occurs when two waves pass through the same physical space and result in a lesser displacement than the original waves.

11. Interference of Waves From Wikipedia, Oleg Alexandrov, Public Domain

12. Beats When two waves of similar frequencies pass through the same medium, the resulting wave is perceived with beats, or periodic alternations of intensity. The frequency of the beats (intensity variation) is equal to the difference in the frequency of the two sources being combined. There are many great applets demonstrating this phenomenon online. Some are linked to below. mta.ca thinkquest.org (with sound) walter-fendt.de Image from Wikipedia, user Army1987, all rights released

13. Interference of Particles (Electrons) Image from NASA

14. Waves diffract, or spread out, when they encounter a barrier that is comparable in size to their wavelength. Waves may even seem to bend around corners if their wavelength is long enough. Diffraction is why the edges of shadows are never sharp, and why you can hear around corners. Diffraction

15. Standing Waves When waves travel in a closed medium, interference of the forward and reflected wave can cause standing waves. Standing waves have nodes (points that have destructive interference and do not move) and antinodes (points that alternate between constructive and destructive interference and have maximum displacement). The result is a pattern that appears stationary. By Catherine Schmidt-Jones, Standing Waves and Musical Instruments, http://cnx.org/content/m12413/1.11/

16. Doppler Effect • The Doppler Effect is the change in frequency between an emitted and detected wave due to the relative motion of the source and observer. • When the source and observer approach one another, the frequency increases. (blue shift) • When the source and observer move apart, the frequency decreases. (red shift) Images from NASA

17. Doppler Effects US Army Photo by Master Sgt. Lek Mateo, Public Domain Image from NOAA, from weather.gov www.haystack.mit.edu

18. Doppler Broadening • The rotational transition in ozone emits a photon at exactly 11.07524545 GHz. • Instead of a single frequency, we detect a range of frequencies, due to the broadening of the signal. • As ozone molecules move towards or away from us, the frequency we detect is slightly higher or lower. • The greater the density of particles or the greater the speed of the particles, the more broadening occurs. © Swinburne University of Technology, used with permission

19. Which Ozone Do We See? • Only 1% of the ozone in the atmosphere is located in the mesosphere. • 99% of the ozone is in the lower atmosphere. The ozone there is more dense, so the signal frequency is spread out due to pressure broadening. • Scientists sometimes distinguish between thermal broadening (as in all parts of the atmosphere, where the temperature is above 0 K) and pressure broadening (as in the lower atmosphere, where the gas is denser). • Pressure broadening in the lower atmosphere results in a very broad and “washed-out” signal at 11.07 GHz. • Thermal broadening in the mesosphere causes some broadening around 11.07 GHz, but not too much, since the mesosphere is not that dense (and not that hot).

20. MOSAIC Setup

21. MOSAIC Spectrum