Electromagnetic Spectrum Flashcards
Radiation Fundamentals
- The fundamental unit of radiation(energy that is emitted by the sun) is the photon/light
- Photons are released from objects when matter:
- is excited thermally
- is engaged in nuclear processes (fusion, fission)
- Photons are also absorbed and reflected by matter
- The speed of photons in a vacuum (c) is 3.0 x 108 m/s but have different energies related to their wavelength
the sun
- 109 times bigger than the Earth
(diameter). - 99.86% of the total mass of the Solar
System. - Surface temperature: 5,800 K
- Energy comes from nuclear fusion of
hydrogen into helium - Emits light in virtually every part of
the EMS
Radiation Fundamentals
We relate frequency and wavelength by:
C = lembda x V
- c = speed of light **(a constant), **
- lambda = wavelength
- v = frequency.
So, we see that as wavelength increases (gets longer), the lower
the frequency (and energy). and vice versa
so frequency
is how many many waves there are in a wave lenght
- lower frequency = less waves= lower amount of energy associated
- high frequency = more waves=high amount of energy associated
EMR Spectrum
- Wavelengths range in size from radio waves which are several meters long, to visible light which is measured in microns or millionths of a meter (10-6 m)
**radio waves: **lenghier waves=less frequecy= less energy
Gamma ray: shorter wave = more frequency =more energy
Radio Waves
- Radio waves have the longest wavelengths in the spectrum
- They range from the length of a football field to larger than our planet
- You can tune a radio to a specific radio amplitude (AM) or frequency (FM)
- And listen to your favorite music
- The radio “receives” these electromagnetic radio
waves and converts them to mechanical vibrations in
the speaker to create sound
Radio Waves and space
- Astronomical objects often produce radio waves
o Thus radio telescopes can view planets, stars, and
galaxies - Since radio waves are longer than optical waves,
radio telescopes must be physically very large - In order to make a clearer, or higher resolution, radio image, radio astronomers often combine
several smaller telescopes, or receiving dishes,into an array
Microwaves
- Microwaves are the portion of waves in the spectrum at the end of the radio spectrum(next to radio waves)
- Most communication satellites use C-, X-and Ku-bands to send signals to a ground station
- Remote sensing using X, C, L and P
- Microwaves that can see through haze, light rain and snow, clouds, and smoke are beneficial for satellite
communication and studying the Earth from space
Infra-Red Waves
- The infrared region is divided into:
- Near
- Mid- (or Short wave)
▪ Near and mid are classified as reflective infrared
- Far-infrared
- classified as longwave emitted infrared
▪ These wavelengths are best for studying the longwave
thermal energy radiating from our planet
Infra-Red Waves and Heat
- Objects emit radiation as they heat up
* The thermal (or far/longwave) infrared radiation that is emitted as an object warms is what we sense as heat
o Some objects are so hot they also emit visible light—such as
a fire
o Other objects, such as humans, are not as hot and only emit
infrared waves
o Our eyes cannot see these infrared waves but instruments
that can sense infrared energy—such as night-vision goggles
or infrared cameras–allow us to “see” the infrared waves emitting from warm objects such as humans and animals
Near Infra-Red Waves
- A portion of radiation just beyond the visible spectrum is referred to as near-infrared
- This is not heat
- It is reflected, transmitted, and absorbed light and it is very useful for observing health of vegetation and soil composition
- Reflected near-infrared radiation can be sensed by satellites, allowing scientists to study vegetation from space
Visible Waves
- All electromagnetic radiation is light, **BUT **the portion of this radiation our eyes can see is called visible light
- The wavelengths of visible light fall out like a rainbow
- Violet has the shortest wavelength, at around 380 nanometers, and red has the longest wavelength, at around 700 nanometers
- Green is in the middle
- Each color in a rainbow corresponds to a different wavelength of electromagnetic spectrum
UltraViolet Waves
- Ultraviolet (UV) light has shorter wavelengths than visible light
- Although UV waves are invisible to the human eye,** some insects, such as bumblebees, can see them**
- The Sun is a source of all UV light
o **UV-C rays are the most harmful **and are almost completely **absorbed by our atmosphere
**
o UV-B rays are the harmful rays that cause sunburn
-
Only a small amount of UV-A waves hit the Earths surface and those are the ones** we use in Earth
observation Ultraviolet Imaging Spectrograph (UVIS)** used to capture imagery of Saturn’s rings (Source: NASA)
X-Ray Waves
*** X-rays **have much **higher energy **and much shorter wavelengths than ultraviolet light
- As a result we often refer to X-rays in energy rather than their wavelength
- Different objects absorb different amounts of x-rays
- Different hot bodies like the Sun and stars all emit x-rays
- We DON’T use X-rays to observe changes on the Earth
Gamma Waves
- Gamma rays have the **smallest wavelengths **and the most energy
- They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova
explosions, and regions around black holes -
On Earth, gamma waves are generated by nuclear explosions,
lightning, and radioactive decay - Unlike optical light and x-rays, gamma rays cannot be captured
and reflected by mirrors
o Gamma-ray wavelengths are so short that they can pass through the
space within the atoms of a detector -
Gamma-ray detectors are usually densely packed crystal blocks
o As gamma rays pass through, they collide with electrons in the crystal
o These collisions create charged particles that can be detected by the
sensor
we dont use them for earth observation
EMR Spectrum
* Gamma rays and x-rays (normally measured in Å) < 10 Å; Earth’s atmosphere blocks this radiation
almost completely.
- Ultraviolet 1-400 nm; Most blocked by Earth’s atmosphere (O3 absorption) except from 300-400 nm.
-
Visible 400-700 nm; peak solar wavelengths; Earth’s atmosphere almost completely transparent
(relatively speaking to other EMR). -
Reflective (near/mid) infrared 700-3000 nm (0.7 – 3.0 m); high absorption by water vapor in the
atmosphere; commonly used by earth observation satellites to monitor vegetation cover/health. -
Thermal (far) infrared 3.0 – 10,000 m; terrestrially derived; absorption by water vapor and CO2 in
atmosphere. - Microwave – 0.1 – 30 cm; wavelengths used in RADAR; atmosphere mostly transparent.
* Radio - > 30 cm; atmosphere almost completely transparent
Surface Interactions
Electromagnetic radiation interacts with features on the Earth’s surface:
It can be
➢absorbed,(convert the enrgy)
➢reflected,
➢and transmitted.
Surface Interactions
- When visible light strikes a leaf, certain light is reflected
o Creating the image of the leaf we see. - The portion not reflected is absorbed or transmitted (which is why some light can be seen through it).
- Absorbed energy raises the temperature of the leaf and is reemitted as heat.
- The leaf’s reflectance and absorption characteristics are what give it the color we perceive.
Surface Interactions
Upon striking the land or ocean surface the incoming radiation partitions into three responses:
- Transmittance - some fraction (up to 100%) of the radiation penetrates into certain surface materials such as water and if the material is transparent and thin, it normally passes through, generally with some diminution(like mirror)
-
Absorption - some radiation is absorbed through electron or molecular reactions within the
medium; a portion of this energy is then re-emitted, usually at longer wavelengths (thermal/heat) - Reflectance - some radiation reflects (moves away from the target) and scatters away from the target at various angles, depending on the surface roughness and the angle of incidence of the rays
These three parameters are dimensionless numbers (between 0 and 1), but are commonly
expressed as percentages.
Surface Interactions and percentages
- Example:
o 60% transmission
o 30% reflection
o How much absorption?
▪ 10% absorption - Total must equal 100%
