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21 Cards in this Set
- Front
- Back
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Remote sensing resolutions |
Resolution: resolving power, ability of an optical system to distinguish between signals that are spatially near or spectrally similar Spectral: the number and size of spectral regions the sensor records data in (blue, green, red, infrared, microwave) Spatial: size of field of view Temporal: how often sensors acquire data Radiometric: the sensitivity of detectors to small diffs in electromagnetic energy
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Passive RS |
radiation that eminates naturally from an object ex: sun, Earth's surface generally needs daylight hyperspectral, multispectral
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Active RS |
system that emits energy provides own energy source can be used day or night requires lots of energy ex: Radar, LiDar, Synthetic Aperture Radar (SAR) |
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electromagnetic spectrum |
A continuum of energy, travels at speed of light the range of all possible frequencies from radiation red-->blue shortest wls- radio/microwaves longest- gamma (fastest)
order: gamma, x-ray UV, visible, infrared, microwaves |
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regions of electromagnetic spectrum used in RS (UV, Visible, NIR, SWIR) |
UV: .3-.4um VIS:.4-.7um NIR: .7-1.3um; emittance energy SWIR: 1.3-3um |
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Conversion of wavelengths from nanometers (nm) to micrometers (um) and vice versa |
1 nm = .0001 um so, 1 um = 1000 nm
10 nm = .01 um 100 nm = .1 um 1000 nm = 1 um 1500 nm = 1.5 um etc... |
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the relationship between frequency and wavelength |
frequency is inversely proportional to wavelength so, the shorter the wavelength, the lower the frequency (and vice versa) |
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How are photons and wavelengths related to the detection of electromagnetic radiation? |
electromagnetic energy can only be detected as it interacts with matter a photodetector: photons interact with it and produces an electrical signal that varies in strength, proportional to # photons measured by two fluctuating fields: electric & magnetic wave concept |
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4 components of RS system |
Energy Source Transmission Path (i.e. Sun) Target: has to bounce off something/reflector to a sensor Sensor/platform |
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Relationship between an object's temp, NRG, and dominant wavelength
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blackbody (theoretical substance that absorbs and radiates energy at the max possible rate per unit at each wavelength for a given temp..the perfect abosrber and emitter... total emitted radiation is proportionate to its absolute temp (stefan-Boltzmann Law))
greater temp = greater amount of radiant energy emitted from object as temp increases its dominant wl gets shorter
Wien's Displacement Law- determine blackbody's dominant wl |
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How does electromagnetic energy interact with the atmosphere and earth? |
Atmosphere: Scattering (Raleigh, Mie, Nonselective) Earth: Reflectance, absorption, transmission |
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Raleigh |
wavelength dependent, mostly in upper 4.5 km of atmosphere
Scattering by particles that are smaller than the wavelength of visible and near infrared radiation...more scattering at smaller wavelengths....blue sky and red sunsets
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Mie |
wavelength dependent, longer wl than Raleigh, lower 4.5 km of atmosphere
Particles in the atmosphere are ~equal in size to the wavelength of the scattered radiation... influences longer wavelengths...dust, pollen, smoke...smog is reddish brown |
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Nonselective |
lower portions of atmosphere
all wavelengths equally affected...particles are larger than the wavelengths...most common...water droplets in clouds...gray haze |
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Absorption |
atmosphere is preventing the transmission of radiation
Ozone (O3 and O2), Water (H2O), and Carbon Dioxide (CO2) are responsible for most of the solar radiation absorption that occurs
absorbed and re-radiated at longer wavelengths atmospheric windows |
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reflectance |
occurs when a ray of light is re-directed as it strikes a nontransparent surface
The nature of the reflection depends on sizes of surface irregularities in relation to the wavelength of the radiation considered
- Specular Reflection: reflection off a smooth object (ie. smooth body of water, mirrors) - Diffuse Reflection : off of rough objects (clothes, roadways, etc) |
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transmission |
occurs when radiation is neither reflected or absorbed, but passes through a substance without significant weakening. |
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wave concept |
explains how electromagnetic energy moves, but must interact with matter for it to be detected |
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atmospheric windows |
what doesn't get absorbed, wavelengths that are easily transmitted |
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incident radiation |
absorbed + reflected + transmitted radiation
law of conservation of energy |
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emittance energy |
mainly derived from shortwave energy from sun that has been absorbed, then re-radiated at longer wavelengths
strongest at the far infrared region
reveals information about thermal properties of materials |
