electromagnetic radiation Flashcards
false color composites
recolor bands as different colros
why understand the EM radiation theory
- explains why EM radiation is distributed the way it is
- explains why objects emit, reflect, absorb, and transmit energy the way they do
- help us to build better sensors
- help us figure out how to detect the things we want to detect
EM radiation: what is it
- Take different forms that have different amounts of energy
- Classification occurs via electromagnetic spectrum
○ Classifies EM radiation according to various characteristics (wavelength or frequency)
EM radiation can be described using
- Wave theory
- Particle theory
wave theory
describe EM radiation in terms of its frequency and wavelength
wavelength equation
c = v(L)
c - velocity of light
v - frequency (cycles/s)
(L) - wavelength (m)
velocity of light: value
3x10^3 m/s
particle theory
describes EM radiation as particles (quanta or photons) with energy
particle theory equation
Q = hv
Q - energy of a quantum
h - Planck’s constant
v - frequency
shorter vs. longer wavelengths
shorter wavelength: higher frequency + more energy
longer wavelength: lower frequency + less energy
visible spectrum order
SHORTEST
UV
blue
green
red
near IR
LONGEST
sensing longer wavelengths
- Because longer wavelengths have less energy, they can be harder to detect
○ We can usually have more spatial detail when measuring the visible part of the spectrum rather than IR
○ typically less spatial detail available for longer wavelengths
how to sense longer wavelengths
- sensor needs to be more sensitive OR
- the source area needs to be larger in order for the sensor to capture enough energy from the target area
black body radiation
emit continuous spectra (i.e. they emit all wavelengths across a range)
- the electromagnetic radiation emitted by an idealized object called a blackbody, which absorbs all incoming radiation and re-emits energy based on its temperature
blackbody: def
An ideal object that perfectly absorbs and emits all wavelengths of radiation. It does not reflect or transmit any radiation.
- absorbs all instant energy and emits it as thermal energy
the sun as a blackbody
the sun almost behaves as a blackbody
- the sun is a source of most of the radiation we measure in remote sensing
blackbody car example
black cars absorb a lot more sunlight and remit it as heat, where as a white car will simply reflect the sun and stay cooler
- Not many black bodies in nature
blackbody: curve
Area of the curve: differs under different temp
Peak of the curve: shifts with shorter wavelengths w/ more energy
earth’s spectral radiance
peak radiance at ~10 nm
differences between the expected and observed spectrum (spectral radiance)
greenhouse gases in the atmosphere absorb certain wavelengths
○ Why can we see the earth? We’re seeing reflected light, not energy emitted by earth
what happens to EM radiation in the atmosphere
- scattering
- absorption
scattering
unpredictable diffusion of radiation by particles in the atmosphere
- type of scattering classified by relative size of wavelengths
types of scattering
- rayleigh
- mie
- non-selective
rayleigh scattering
particles smaller than wavelengths
- magnitude of scattering inversely proportional to wavelength
- scattering is equal in all directions
- Always lots of nitrogen, oxygen, CO2 in the atmosphere
○ Blue wavelengths are scattered about 5x more than red wavelengths because they’re shorter
○ Blue wavelengths are more likely to hit the smaller molecules
