GEOG 271 Flashcards
Rayleigh scatter
diameter of matter < wavelength of incident microwave radiation
ie. scattering of blue light by atmosphere (small specks of dust or nitrogen and oxygen molecules)
Mie scattering
diameter of matter is approximately equal to wavelength.
ie. scattering from dust, pollen, smoke and water vapour
Non-selective scattering
diameter of matter is several times larger than incident radiation.
ie. water droplets and large dust particles (visible light)
Blackbody
Emits a continuous spectrum of radiation across the EM spectrum proportional to its physical temperature.
The wavelength that is emitted with the most intensity (peak spectral exitance) is determined by its temperature.
Hotter objects emit peak spectral exitance at shorter wavelengths.
Blackbodies absorb and emit energy at the same rate. Good absorbers are good emitters.
ε = 1
Grey body
Object that emits a fraction of the radiation of a blackbody, governed by the object’s emissivity
emissivity (ε) is the ratio of radiant energy of an object compared to that of a blackbody at the same temperature.
Blackbody: ε= 1
Greybody: ε < 1
emissivity (ε) definition + 2 facts
the ratio of radiant energy of an object compared to that of a blackbody at the same temperature.
Emissivity has great influence in passive microwave emissions as the depth of emission of media may be well below the surface.
Shorter frequency thermal infrared is less affected by emissivity as the shorter wavelenths are emitted at depth much closer to the surface (ie. skin temperature)
Selective radiator
Emits radiation of varying intensity at different wavelengths, depending on the object’s emissivity at those wavelengths.
Absorptance
fraction of incident radiation that is absorbed
Brightness temperature
TB is a descriptive measure of radiation in terms of the temperature of a hypothetical blackbody emitting an identical amount of radiation at the same wavelength
Defined as the product of the emissivity and the physical temperature of the surface
Thermal capacity
The ability of a material to store heat
Water has highest thermal capacity- stores heat very well relative to all other materials
Thermal conductivity
Rate that heat will pass through a material.
Many rocks and soils are poor conductors of heat.
Important to know for diurnal studies, with heat increasing/ decreasing throughout the day.
Thermal inertia
Measurement of thermal response of a material to temperature changes.
How long does an object hold on to heat (and how much heat)?
How long does it take an object to heat up/ cool down?
What implication does this have for remote sensing?
- Rocks/water = high thermal inertia (long time to heat/cool)
- Sand = low thermal intertia (heat/cool quickly)
Relative complex dielectric permittivity (complex dielectric constant) ε*
describes the basic electrical properties of a material, which determine electromagnetic (EM) wave propagation, scattering, reflection, attenuation, and (for passive sensors) emission.
Two components:
Real part: ε’
Imaginary part: ε”
Real part: ε’ (component of relative complex dielectric permittivity)
Referred to as ____________.
Describes ___________.
Definition + 2 examples.
Referred to as relative dielectric constant or relative permittivity.
Describes what happens when electric field interacts with an object’s boundary (Reflection)
Sets the absolute backscatter level (ie. the degree of scattering is proportional to its dielectric constant). When microwaves are incident upon an object, if the permittivity of the first medium greatly constrast that of the second, the incident microwaves will be reflected.
ie. (1) Air and Ice (2) Ice and Water
ε’ (air) = 1, ε’ (ice) = 3.17, ε’ (water) = 80
1) ε’(air) - ε’(ice): low contrast; transmission of signal into medium
2) ε’(ice) - ε’(water): high contrast; reflection of signal
Imaginary part: ε” (component of relative complex dielectric permittivity)
Referred to as ____________.
Describes ___________.
Definition + 2 examples.
Referred to as dielectric loss.
Describes ability of material to dissipate penetrated energy (absorption). AKA how much energy is lost in the material volume once it passes across a dielectric interface.
When microwaves are incident upon an object, if the loss factor is high, the material will absorb, and none returned to the sensor
ie. (1) Ice, (2) Water
1) ε”(ice): 0.000065 (low loss)- transmission of microwaves through ice
2) ε”(water): 18.41 (high loss)- absorption of microwaves due to H20 molecule excitation
Atmospheric windows
Regions in the electromagnetic spectrum where the wavelengths of incoming solar radiation or emitted radiation from the ground are largely not absorbed by molecules in the atmosphere
Important atmospheric absorption bands
O2: 0.1- 0.3 & 0.7
H20: 1 & 5.5-7
CO2: mid-infrared (1.3-3) and thermal infrared (3-5) & 10.5-12.5)
O3: 8-14
Thermal infrared (3-14): absorption from:
CO2 (3-5 & 10.5-12.5), H2O (5-8) and O3 (8-14) - Greenhouse effect in this region
Path radiance
Paths 2,4: radiance observed at the sensors from areas other than the study area
Atmosphere Effects
Energy-matter interactions in the atmosphere, at the surface, and a the remote sensing system (sensor)
What does atmospheric correction do?
What causes haze?
Removes haze/path radiance
Haze caused by:
- high level clouds
- O2
- H2O
____________ surfaces act as specular reflectors and ____________ energy ___________ from the surface
(Active Microwave)
Smooth, reflect, away
