Weeks 8-10 Flashcards
How does an active system work?
sensor transmits energy towards target, energy interacts with target, producing backscatter, energy returns to sensor and is measured
when does scattering/absorption occur?
when the wavelength of incident EMR approximates size of scatterers or targets
what does polarization influence?
types of interaction that occur at targets and the amount of radiation returned (backscatter)
what are the three types of polarizations?
co-polarized (HH), cross-polarized (HV), quad-polarized (HH+HV+…)
what are the advantages of RADAR?
low frequency/long wavelength (all-weather), operates when told, permits shallow look angles, senses outside visible/infrared, synoptic views of large areas
what is the backscatter coefficient and what does it determine?
the RADAR cross-section reflected back to the receiver, determined the amount of energy reflected back to the RADAR from within the cell
what is foreshortening (geometric distortions)?
when the object appears shorter than it actually is because it is angled towards the viewer
what is layover (geometric distortions)?
when the order objects are represented in relation to a ground projection is reversed, RADAR beam reaches top of feature before the base
what is shadowing (geometric distortions)?
RADAR beam is unable to illuminate ground surface
smooth vs rough surfaces and RADAR interaction
smooth - act as specular reflectors, reflect energy away from the sensor
rough - act as diffuse reflectors, causes backscatter
what is complex permittivity?
describes the potential for a material to transmit, reflect, and absorb microwave energy
what are the three scattering mechanisms?
surface, double bounce, volume
RADAR surface interactions with water
uses surface roughness of sea waves to quantify sea winds, oil spills have extremely low backscatter and are visible
what is permittivity used for in RADAR?
electrical properties, permittivity increases in presence of water, can be used for measuring surface’s moisture levels
what are some active microwave applications?
vegetation (canopy thickness, crop type, etc), fire disturbances, monitoring cryosphere, monitoring lake ice
