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Remote Sensing > chapter 9 RADAR > Flashcards

chapter 9 RADAR Flashcards

1
Q

active microwave (RADAR) based on transmission of …

A

long-wavelength microwaves (3-25 cm)

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2
Q

LIDAR base on…

A

transmission of short-wave laser light (0.9 um)

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3
Q

SONAR based on …

A

transmission of sound waves through a water column

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4
Q

SLAR stands for

A

real aperture Side-Looking Airborne Radar

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5
Q

SAR stand

A

synthetic aperture radar

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6
Q

sent out by the transmitter through the antenna

A

pulse

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7
Q

pulse length is measured in

A

microseconds (usec)

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8
Q

microwave energy usually measured in

A

cm

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9
Q

microwave wavelengths that can penetrate clouds

A

L = 15.0 - 30.0 cm

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10
Q

RADAR can penetrate…

A

vegetation, sand, snow

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11
Q

RADAR allows resolution to be…

A

independent of distance to object

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12
Q

RADAR can operate simultaneously in …

A

multiple wavelengths

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13
Q

azimuth _______

A

azimuth flight direction refers to the straight line the aircraft travels in

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14
Q

look direction is called..

A

range

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15
Q

terrain illuminated nearest the aircraft

A

near-range

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16
Q

terrain illuminated farthest from the aircraft

A

far-range

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17
Q

Objects that trend perpendicular to the range are

A

enhanced

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18
Q

Objects that trend parrallel to the range

A

less enhanced

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19
Q

depression angle

A

the angle between a horizontal plane extending out from the aircraft fuselage and the electromagnetic pulse of energy from the antenna to a specifc point on the ground

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20
Q

average depression angle

A

avergage betwen near-range and far-range depression angles

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21
Q

incident angle

A

angle between the radar pulse of EMR and a line perpendicular to the earth’s surface where it makes contact. If the terrain is flat the incident angle the complement of the deppession angle. If the terrain is sloped there is no relationship between the two. Many radar studies assume the terrain is flat.

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22
Q

unpolarized energy

A

vibrates in all possible directions perpendicular to the direction of travel

23
Q

polarized energy sent out by radar antennas

A

pulse of energy is filtered so that its electrical wave vibrations are only in a single plane that is perpendicular to the direction of travel. the pulse can be sent out vertically or horizonally

24
Q

HH and VV

A

like-polarized

25
Q

HV and VH

A

cross-polarized

26
Q

uncorrected radar imagery displayed in…

A

slant-range geometry (based on the actual distance from the radar to each of the respective features in the scene)

27
Q

converted slant-range display

A

true ground-range display

28
Q

to determine spacial resolution at any point in a radar image, you must compute two dimensions…

A

range and azimuth

29
Q

the range resolution in the across-track direction is proportional to the length of the…

A

microwave pulse

30
Q

the shorter the microwave pulse…

A

the finger the range resolution

31
Q

pulse length is a function of the speed of light (c) multiplied by

A

the duration of the transmission (t)

32
Q

range resolution (R) at any point between the near and far-range of the illuminated strip can be computed if these two are known:

A

depression angle of the sensor at that location and the pulse length

33
Q

pulse length can be converted to distance by…

A

multiplying it by the speed of light

34
Q

The equation for coimputing the range resolution

A

tau = pulse length

c = speed of light (3 x 10^8 m/s)

gamma =depression angle

35
Q

Azimuth resolution

A

determined by computing the width of the terrain strip that is illuminated by the radar beam

36
Q

Real aperture active microwave radars produce a….

A

lobe-shaped beam which is narrower in the near-range and spreads out in the far-range.

37
Q

in real aperature active microwave, the longer the wavelength…

A

the wider the (lobe-shaped) beam width. and the shorter the wavelength, the narrower the beam width

38
Q

In real aperture radars, a shorter wavelength pulse, the…

A

the better the azimuth resolution (and the poorer the atmospheric and vegitation penetration)

39
Q

Beam width is ____ to antenna length

A

inversely proportional

40
Q

the longer the radar antenna, the ____ the beam width and ____ azimuth resolution

A

narrower, higher

41
Q

relationship between wavelength and antenna length to compute azimuth resolution (formula)

A

L = antenna length

S = slant-range distance to point of interest

42
Q

graphed azimuth resolution

A
43
Q

graphed range resolution

A
44
Q

foreshortening

A
45
Q

layover

A
46
Q

radar relief displacement

A

the horizontal displacement of an object in the image caused by the objects elevation. The higher the object, the sooner it is detected on on the radar image

47
Q

foreshortening infuenced by three things:

A

object height

depression angle

location of objects in the across track range (features in the near-range are foreshortened more than identifcal features in the far)

48
Q

foreshortening causes features to appear to have …

A

steeper slopes than they actually have in the the near range and shallower slopes that than they actually have in the far range

49
Q

image layover is an extreme case of ___________

A

foreshortening (occurs when incident angle is smaller than the forslope)

50
Q

in synthetic aperture radar systems, engeneers have developed

A

a way to synthesize a very long antenna electronically. Additional beams are sent toward the object. doppler principles are then used to monitor the returns to synthesize the azimuth resolution to become one very narrow beam.

51
Q

there is a relationship between the ___ of the radar, the _____, and the height of local objects

A

wavelength, depression angle

52
Q

the _____ can be used to predict what the earth’s surface will will look like in a radar image if we know the surfice roughness, wavelenth, and depression angle

A

modified Rayleigh criteria

53
Q

graph of surface roughness

A
54
Q

response of pine stand to 23.5 cm, 5.8 cm, and 3 cm wavelenths

A

Remote Sensing (10 decks)

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