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4066 final Flashcards

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1
Q

what is back scatter a combination of.

A

characteristics of the sensor (wavelength/frequency, incedence angle polarisation and look direction)
characteristics of the target (shape, roughness, dielectric constant)

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2
Q

what is a coherent point target

A

special radar reflection conditions (target shape) where level of backscatter out or proportion to feature size.(common in urban areas)

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3
Q

what are the three types of corner reflectors and to what orientation do they work best

A

top hat- both
dihedral- two flat surfaces at right angle- horizontal
trihedral- three flat surfaces that are perpendicular- vertical

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4
Q

what is the difference of HH and VV backscatter

A

HH usually double bounces up down whereas VV double bounces left right

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5
Q

what is specular reflectors

A

horizon smooth surface reflect nearly all incident energy away from the radar (water)

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6
Q

what is diffuse reflectance

A

rough surface, energy is scattered in wide range of angles.

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7
Q

what is volume scattering

A

multiple scattering of radar signals within a medium. e.g. veg canopy, then wood, then soil, then bedrock. or surface and rock under.

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8
Q

how can you calculate roughness

A

modified Rayleigh criteria- can be used to predict earth surface if we know the surface roughness characteristics and radar system params

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9
Q

smooth and rough Rayleigh criteria

A

quantitative expression of the smooth criteria (like specular reflector) is:
h< wavel/ 25 sin

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10
Q

what is the dielectric constant

A

a measure of a materials electric properties includes the degree it absorbs, reflects and transmits micro radiation in response to an incident signal

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11
Q

what has a high and low dielectric constant

A

high- water, salt, metals, living veg
low- rocks, lake ice, dry soils, dry sands, and dead vegetation

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12
Q

the difference between ice and water is seen on what type of orientation

A

HH

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13
Q

what is the cardinal effect

A

urban areas often laid out according to cardinal points on a compass. increase of backscatter when radar is perpendicular to its orientation

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14
Q

where is low spectral resolution found

A

usually level 1 with older satellites and new expensive ahh satelites

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15
Q

what can SAR extract in terms of biophysical parameters

A

canopy water content
vegetation type
biomass
canopy structure

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16
Q

what is surface scattering vs volume scattering

A

surface scattering- bright returns in like-polarised energy from single reflections of canopy
volume scattering- energy scattered multiple times often depolarised.

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17
Q

what is the relationship with wavelength and penetration

A

longer wavelength greater penetration

different bands are x band shorter wavelength( leaves small branches)
L band volume scattering (stems)
p band (trunks and soil surface)

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18
Q

how does back scatter interact with biomass

A

linear relationship

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19
Q

what does a greater return on cross polarisation mean

A

greater contribution for volume scattering
cross polarisation less sensitive to slope variations

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20
Q

what are considerations when selecting incident angles

A

steep incident angle- less return from architecture more sensitive to moisture
shallow incident angle- structure of tree contributions more to backscatter

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21
Q

what are two planning considerations when acquiring data

A

use seasonal change to your advantage
select time of acquisition

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22
Q

what is radar imagery

A

series of short pulses-backscatter is received and stores in a series of time delays

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23
Q

what is signal history

A

sar records info on how much radar signal interacts with targets in both range and azimuth directions

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24
Q

what is compression processing

A

convert the history in the range and azimuth direction in a 2D gridded format whose basic subdivision is the slant range resolution cell

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25
what is slant range resolution
the minimum distance between two targets that can be distinguished along the radar's line of sight, or slant range
26
what is multi looking
a signal processing procedure that reduces the amount of speckle in the image
27
what are the 2 ways to perform multi looking
having multiple single look images and average it processing the data to full resolution and spatially averaging the image
28
what are the two types of geometric correction
slant range to ground conversion geometric rectification (true shapes and orientations usable as a map
29
what are the two types of radiometric calibration
absolute and relative absolute- establish a time-independent correlation between image or brightness on a SAR image & backscatter from target relative- establish a constant correlation between intensity (or brightness) on image & backscatter
30
what is the dynamic range of radar signatures
ratio of the largest return to the smallest (background noise/noise floor)) -determined by the targets, frequency, resolution & imaging geometry
31
31
what is data integration (fusion)
integration of Multidate or multifrequency radar data, or of radar data with optical data may aid in the interpretation process
31
what are non adaptive filters
mean filter- intensity at each sample interval in image replaced by the mean of pixel values in a moving window median filter- assigns the window median value to each sample NOT RECOMMENDED FOR RADAR
32
what are adaptive filters
modify image based on statistics extracted from local environment of each pixel
33
what's the frost filter
unspeckled pixel value is estimated using a subwindow of the processing window
34
whats the lee filter
unspekled pixel value is a weighted sum of the observed pixel value and the mean value
35
what are edge detection filters
classical edge detectors developed for imagery not suitable for SAR
36
what are the 6 visual interpretation techniques
tone texture pattern size shape association
37
what is a relief distortion
horizontal displacement of objects in image in a direction towards the radar antenna caused by objects elevation
38
what is foreshortening
akk terrain that slope inclined toward the radar will appear compressed or foreshortened relative to slopes inclined away from the radar
39
what are ther 3 factors that effect foreshortening
object height (heigher height more foreshortening) depression angle (or incident angle) higherdepression angle or lower incident angle, higher foreshortening location of objects in the across-track range (closer to sensor more foreshortening)
40
what is layover
an extreme case of image foreshortening. occours when incident angle is smaller than foreslope. beam reaches the top before it reaches the bottom. top will point towards sensor
41
what is shadow
obscure information behind tall landfeatures
42
what is speckle and fading
grainy salt-and-pepper pattern in radar imagery present due to the coherent nature of the radar wave, which causes random constructive and destructive interference, and hence random bright and dark areas in a radar image
43
what is the difference between obstructivbe and destructive interference
constructive make white spots as they amplify the wavelength. destructive cancel eachother out and result is black
44
how can you fix speckle and fading
multiple looks and averaging it out.
45
what is the doppler principle
frequency (pitch) of a sound changes if the listener and/or source are in motion relative to one another
46
what is the zero doppler principle
pitch will be highest when it is directly perpendicular to the listener
47
what is radar backscatter coefficient
the amount of radar cross-section, reflected back to the receiver, per unit area (a) on the ground:
48
what size should the radar wavelength be set too
to the size of the features you wish to discriminate
49
what are benefits and drawbacks of high vs low frequencies
High- need more power more difficult electronics Low- more difficult processing need larger antennas and feeds simpler electronics
50
what is the azimuth direction
direction on the ground parallel to the motion of the SAR sensor platform
51
whats the look (range) direction
direction in which the signal is transmitted. perpendicular to azimuth
52
what is nadir
point directly below the SAR sensor platform
53
what is the depression angle
the angle created from a horizontal line extending from the sensor measured down to the beam
54
what is the illumination angle
the opposite of depression. line straight down to ground from sensor measured upwards to top of beam
55
what is the incident angle
angle angle from the far edge of the beam to a line perpendicular to the ground. when terrain isn't flat it is 90-depression angle
56
what is a range vector
a vector representing the direction and distance from SAR platform to earth surface being imaged during a single transmitted pulse
57
difference between slant range and ground range
slant range- distance from sensor to target located in the range direction ground range- the slant range projected on earths surface difference is that the slant is measured from top of beam and ground is on the ground duhh
58
what is range resolution
across track direction the ability of radar system to distinguish between two or more targets on the same bearing but at different ranges ground range is how wide a building is range resolution is how wide the beam thinks it is
59
what is pulse length
speed of light times length of transmition
60
what is azimuth resolution
determined by computing the width of the terrain strip that is illuminated by the radar
61
what does RADAR stand for
radio detection and ranging
62
what is the 3 primary operations of radar
transmits microwave pulses towards target receives returned portion of transmitted signal (backscatter) after it interacts with a target observes strength and time delay of returned signals
63
when did radar begin
1950s US military declassified 1960s
64
does cross pol or like pol have stronger back scatter
like pol
65
what are the different bands and what are their functions
K very short used in old school not as much now L band 15-30cm S band 8-15cm C band 5-10cm X band 3cm

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