Unit 9

Question 1

Define passive microwave

Answer 1

sensors detect emitted terrestrial radiation

Question 2

define radar alimetry

Answer 2

ranging sensors that measure elevation of land or water surfaces

Question 3

define radar scatterometers

Answer 3

microwave radiometers that measure scattered energy off of land and water surfaces

Question 4

microwave remote sensing that includes imaging and ranging sensors that detect intensity and phase of backscattered energy

Answer 4

synthetic aperture radar (SAR)

Question 5

How far does the microwave region range? Why does this matter?

Answer 5

Ranges from mm scale to m scale wavelengths. The wavelength used by a sensor dictates what interacts with it and what we see. For example it won’t be cell structures or chemical reactions.

Question 6

What is the major benefit of microwave remote sensing?

Answer 6

Since larger than molecules we can see through clouds as they don’t interact = spaceborne remote sensing works great

Question 7

Are microwave remote sensors (ex. Radar) active or passive and why?

Answer 7

Active, because the wavelength of the sun is too small to see the reflected energy

Question 8

What is a major application of Radar remote sensing (such as SAR)?

Answer 8

Disaster response since often there are too many clouds in a storm to see through = helps for figuring out what regions are flooded and need help

Question 9

How is SAR similar to LIDAR but different?

Answer 9

Both measure the distance from the detected features on the ground to the sensor using pulses (echo), BUT the distance is a slant range/side looking for SAR

Question 10

What are some of the downsides to the side-looking aspect of SAR?

Answer 10

causes foreshortening, layover, and shadowing

Question 11

What is foreshortening in regards to SAR?

Answer 11

SAR sensor looks towards a hillslope = length of time to reach the far side is longer making the facing side look compressed
*higher the object is the more it slants towards the direction of viewing

Question 12

what is layover in regards to SAR?

Answer 12

When a slope is steep the echo from the top may reach the sensor before the base = looks closer than the base
*can help us infer the height of an object

Question 13

What is the term in SAR for when energy does not reach an area due to obstruction such as a hill?

Answer 13

Shadowing

Question 14

What are the three backscatter mechanisms?

Answer 14

Surface scattering, specular reflection, and double-bounce back scattering
*review each

Question 15

How does the x-band, c-band, and l-band differ when looking at a forest?

Answer 15

The x-band will only show the leaves in a closed canopy, c-band will show the middle or volume of the canopy such as leaves and branches, l-band the canopy top is invisible which makes it best for biomass or flooding on the forest floor analysis

Question 16

What is polarization of light?

Answer 16

The orientation of the light in space

Question 17

What polarization does sunlight have?

Answer 17

it is randomly polarized

Question 18

How does polarization related to active radar systems?

Answer 18

We can measure the depolarization in addition to the amount of echo to infer what interaction occurred with what. For instance measuring how much vertical vs horizontal was returned based on the polarization of energy sent out

Question 19

What is the different between dual polarized and quadrature polarized systems?

Answer 19

Dual transmit either V or H and receive both, Quadrature transmit both V and H and receive both

Question 20

What is an example of a dual, quadrature, and circularly polarized system

Answer 20

Sentinel-1
RADARSAT-2
RADARSAT Constellation Mission

Question 21

What is the downside of quadrature polarized systems? And what would be the solution

Answer 21

They cannot look as far = smaller images because they require more energy to send two pulses
Instead use a dual pol system to look further

Question 22

What backscatter mechanisms stand out in which polarization?

Answer 22

single or double bounce scatter stand out in VV because the horizontal is week in these mechanisms

Question 23

What would have a higher horizontal backscatter?

Answer 23

dense clustered vegetation like canopies = forests have a greater H than agricultural areas (volumetric scattering)
This leads to increased depolarization

Question 24

What is polarimetric decomposition?

Answer 24

Converting the backscatter intensity and phase of each pixel and the polarization to interpret the backscatter properties
ex. high volumetric may be a forest or shrub land

Question 25

What is the phase of a wave?

Answer 25

The position of a wave at any given time

Question 26

What is a phase shift of a wave?

Answer 26

When there is a difference in phase between two waves

Question 27

Why is phase important in SAR?

Answer 27

the relative phase between two EM waves will tell use about the difference in distance travelled between the two

Phase shifts tell us the differences in path lengths of returned energy in SAR

Question 28

How can we use phase shifts in SAR?

Answer 28

To derive height information or changes in height over time

Question 29

How can fringes in SAR interferometry be applied?

Answer 29

Can measure displacement caused by earthquakes and eruptions OR can measure lad subsidence which is the lowering of the land such as from sinkholes