Synthetic Aperture Radar (SAR)

Question 1

What is RADAR an abbreviation of?

Answer 1

Radio Detection and Ranging

Question 2

What is LiDAR an abbreviation of?

Answer 2

Light Detection and Ranging

Question 3

What are the swath angle limits for InIRA?

Answer 3

1° - 8°

Question 4

What are the swath angle limitsfor SAR?

Answer 4

20° to 60°

Question 5

what do basic altimeters use?

Answer 5

nadir ranging

Question 6

what does nadir ranging use?

Answer 6

echolocation

Question 7

What does the shape of the sea surface give you?

Answer 7

It helps infer the shape of the sea floor

Question 8

Explain diffraction limited resolution.

Answer 8

The aperture diameter size determines the footprint size. There is destructive interference on the sides which limits the footprint.

Question 9

what is the angular resolution equation?

Answer 9

angular resolution = (1.22*wavelength )/ aperture diameters

Question 10

What is the resolution of satellite RADAR?

Answer 10

10s of Kms (microwaves sent out with 10s of cm wavelengths)

Question 11

What is the resolution of Lidar?

Answer 11

10s of meters, the wavelength is hundreds of nanometers

Question 12

What is the advantage of side looking radar?

Answer 12

You can differentiate the sides of things and improves range resolution

Question 13

What footprint does side looking radar leave?

Answer 13

An ellipsoidal footprint

Question 14

How does side looking radar work?

Answer 14

As the satellite travels, return signals are collected from multiple pulses and patched together.
There is a Doppler effect - travelling towards and away. This is used to help resolve resolution from ground images.

Question 15

What returns to the sattelite when the surface is completely flat?

Answer 15

Nothing

Question 16

What kind of surface reflects the more signal back to the satellite?

Answer 16

A rough surface

Question 17

What situation leads to total backscatter?

Answer 17

corner reflector (conainer ships)

Question 18

How does RADAR imagery detect oil spills?

Answer 18

Tit can pick up a change in surface tension which affects the reflection

Question 19

What is InSAR

Answer 19

Interferometric Synthetic Aperture Radar

Question 20

What is an amplitude image made up of?

Answer 20

backscatter energy

Question 21

What does the phase image look like?

Answer 21

random pixels, no pattern visible in level 1

Question 22

what is the single look complex?

Answer 22

the amplitude and phase before they’re combined

Question 23

We can’t measure the number of wavelengths from the satellite to the target and back, what do we do?

Answer 23

we look at the phase difference?

Question 24

how is phase measured?

Answer 24

in a 2 pi cycle

Question 25

What did the 2000 SRTM mission do and how long did it take?

Answer 25

the Shuttle Radar Topogrpahy Mission mapped topography within +-60° latitude in 11 days using a 60m baseline

Question 26

What does InSAR do?

Answer 26

It calculates the phase shift resulting from ground movement following an earthquake

Question 27

What is coregistration?

Answer 27

Its the aligning of the image prior and post earthquake

Question 28

What is the required accuracy for co- registration?

Answer 28

1/8 of a pixel to meet the requirement of interferometry

Question 29

What are the requirements for co registration?

Answer 29

the SAR properties must be the same (wavelength, bandwidth and view direction), the co-registration must be <10% and the baseline needs to be small

Question 30

What calculation is done to show ground movement?

Answer 30

phase A - phase B

Question 31

How do you determine the deformation?

Answer 31

counting fringes

Question 32

What does phase unwrapping do?

Answer 32

it smooths out the interferogram by adding segments, check graph in one note

Question 33

What happens when the difference between two pixels in more than 2 pi?

Answer 33

the deformation is too drastic and the interferogram becomes incoherent

Question 34

How do you calculate average ground velocity using InSAR?

Answer 34

Stacking interferograms. You add up interferograms and divide by total time

Question 35

InSAR can measure very slow deformation but what can impact the precision of the readings

Answer 35

Atmospheric noise

Question 36

What is the signal to noise ratio?

Answer 36

look up

Question 37

What can be derived from the interferogram network?

Answer 37

the velocity (ground displacement over time)

Question 38

Why does pointing angle change between ascending and descending line of sight velocity maps?

Answer 38

because the earth is rotating as the satellite passes

Question 39

What does interseismic strain rate inform?

Answer 39

It informs seismic hazard

Question 40

What can be an issue in interpreting vertical InSAR velocities?

Answer 40

permafrost deformation/ melting, groundwater extraction for farming, blocked drainage, mining

Question 41

what is blocked drainage and how does it look in an interferometry map?

Answer 41

it’s the uplift from water trying to exit the basin under a mountain

Question 42

What will future satellites provide?

Answer 42

a 3rd line of sight, providing a norht/ south deformation, allowing us to measure deformation in 3D

Question 43

What will the BIOMASS mission provide?

Answer 43

biomass density with 1 pass (using SAR polarimetry), canopy height with 2 (polarimetric SAR Interferometry) and with multiple you can measure density at different heights (SAR tomography)