GEOG 271 Final Flashcards
what is spatial resolution?
the size of individual pixels (10x10m)
what is spectral resolution?
the number and size of spectral regions the sensor records data in (blue, red, near-infrared, thermal infrared, microwave - radar)
what is temporal resolution?
how often the sensor acquires data at the same location (every 30 days)
what is radiometric resolution?
the sensitivity of detectors to small differences in electromagnetic energy
what is a blackbody?
an object that absorbs and emits all energy that falls upon it
what does the stefan-boltzman describe?
the total amount of energy being radiated
what does wien’s equation describe?
the dominant wavelength of the EM radiance of an object
what is quantum theory of EMR?
energy is transferred in discrete packets called quanta or photons (particle theory)
what does plancks equation describe?
the radiance of an object at a given temperature at any wavelength, an object will emit radiation in all wavelengths but not equally
what does snells law show?
the incident energy is bent from its normal trajectory as it travels from one atmospheric layer to another
when does rayleigh scattering occur?
when particles are very small compared to the wavelength of the radiation (shorter wavelengths like blue are more efficiently scattered)
when does mie scattering occur?
when the particles are just about the same size as the wavelength of the radiation (more scatter than rayleigh, wavelengths scattered are longer)
what are the three main atmospheric constituents which absorb radiation?
ozone, carbon dioxide, and water vapor
when does nonselective scattering occur?
when the particles are much larger than the wavelength of the radiation (all wavelengths are scattered in equal proportions like white light)
what are atmospheric windows?
those areas of the spectrum which are not severely influenced by atmospheric absorption and are useful to remote sensors
what is specular reflection?
the average surface profile is several times smaller than the wavelength of radiation (smooth)
what is diffuse reflection?
the reflected rays go in many directions (rough)
what is lambertian reflection?
the radiant flux leaving the surface is constant for any angle of reflectance to the surface normal
what are the 7 things to keep in mind when thinking of color composites?
color, tone, size/shape, pattern, texture, shadow, and association
what are vegetation indices?
algebraic combination of remote sensing bands to provide additional information about vegetation in the image
what are the advantages of vegetation indices?
it minimizes the disturbing influences (soil background, irradiance, solar position, yellow vegetation, and atmospheric attenuation)
what is the best wavelength for discriminating land from pure water?
near-infrared and middle-infrared (740-2,500 nm)
what is reflectance impacted by in soil (5 things)?
soil texture, soil moisture content, organic matter content, iron-oxide content, and surface roughness
pros and cons of satellite platform
pros - covers larger area, collect imagery on systematic and repetitive basis, systematic geometric distortions
cons - restricted to collect certain areas during a specific time, more difficult to fix/repair a sensor
pros and cons of aerial platform
pros - flexible schedule and revisit time, high and variable spatial resolutions
cons - covers a smaller area, more sources of geometric distortions
passive vs active sensor types
passive - source of energy is either the sun or earth
active - source of energy is part of the remote sensor system
(similar to taking a picture with flash - active - or no flash - passive)
what are 3 applications of remote sensing?
vegetation disturbance (fire), water monitoring (droughts), and lake ice cover
what are the 2 key principles to understanding thermal infrared radiation?
- how energy from the sun or from the earth interacts with the various terrain components
- how the detectors function as they record the terrain’s emitted thermal infrared electromagnetic radiation
what are 3 different passive microwave satellites?
spectral sensor microwave imagery (SSM/I), advanced microwave scanning radiometer (AMSR, AMSR2), and tropical rainfall measuring mission (TRMM) Microwave Imager (TMI)
how does passive microwave interact with soil?
data comes from layer where the thickness is proportional to the size of the wavelength used
how does passive microwave interact with vegetation?
signal received is a combination of the emission from vegetation layer and the ground surface
how does passive microwave interact with snow?
temperature controlled by air temperature and the depth of the snow, snow causes scattering, reducing energy escaping the snow
how does passive microwave interact with sea ice?
ice emits radiation at higher rate than seawater, similar to snow on land
how does passive microwave interact with lake ice
brightness temp increases with ice thickness from increase in emissivity
what is one use for passive microwave remote sensing?
weather observation, measuring rainfall
what are some differences between active and passive remote sensing systems?
passive - relies on electromagnetic energy reflected or emitted from external source
active - emits its own source of EM radiaiton
advantages of active microwave systems
low frequency, operates at user-specific times, permits shallow look angles, senses outside visible/infrared, synoptic views of large areas
how do active microwave systems work?
sensor transmits energy towards target, energy interacts with target, producing backscatter, energy returns to sensor and is measured
what are the 3 types of polarizations?
co-polarized - system transmits and receives the same polarization (HH/VV)
cross-polarized - system transmits and receives the opposite polarization (HV/VH)
quad-polarized - transmit and receive both all combinations (HH+HV+VV+VH)
directions, angles, and range of RADAR scene
azimuth direction, look/range direction, depression angle, look angle, incidence angle, local incidence angle, slant range, ground range
real aperture RADAR vs synthetic aperture RADAR
real - use an antenna of fixed length, limited to resolution than antenna length creates
synthetic - use an antenna of fixed length, able to synthesize larger antenna, able to resolve at higher spacial resolution
what is foreshortening distortion?
the steep slope on the front side reflects a great deal of incident energy back to the sensor, gradual side has less incident energy and appears dark
what is a layover distortion?
extreme foreshortening, the peak backscatters energy before the pulse reaches mountain base, happens when incidence angle is less than the fore slope
what is shadowing distortion?
back slope of terrain is greater than depression angle, no illumination by sensor
what is microwave radiometry?
PM sensors detect microwave energy at various frequencies and polarizations and convert to brightness temperature
advantages to passive microwave remote sensing
penetrates clouds, partially penetrate vegetation so can calculate soil moisture and vegetation properties, and is independent of solar radiation
disadvantages to passive remote sensing
larger instantaneous fields of view, emissivity is subject to change, polar satellites provide discontinuous temporal coverage of equatorial regions
how does surface roughness affect RADAR imagery?
smooth surface acts as specular reflectors, rough surfaces act as diffuse reflectors
permittivity vs complex permittivity
permittivity - ability of molecules to become polarized when a microwave is applied
complex permittivity - potential for a material to transmit, reflect, and absorb microwave energy
what are the three mechanisms for scattering?
surface, double bounce, volume
what is the impact of different wavelengths on RADAR observations?
smaller wavelengths have better resolution, but more trouble with longer ranges
what is hyperspectral remote sensing?
combines imaging and spectroscopy (study of absorption and emission of light) to gather detailed information about the earth’s surface
what is LiDAR?
light detection and ranging, uses light in a laser to measure ranges to the earth
what is GNSS-R?
uses surface-reflected GNSS signals to infer information about earth’s surface
what is Altimetry?
a device that measures the altitude of an object above a fixed level, such as sea level or ground level
advantages of drones
flexibility in monitoring, ease of use, high quality/resolution imagery, flexibility for sensors
