Synthetic Aperture Radar (SAR) Flashcards
What is RADAR an abbreviation of?
Radio Detection and Ranging
What is LiDAR an abbreviation of?
Light Detection and Ranging
What are the swath angle limits for InIRA?
1° - 8°
What are the swath angle limitsfor SAR?
20° to 60°
what do basic altimeters use?
nadir ranging
what does nadir ranging use?
echolocation
What does the shape of the sea surface give you?
It helps infer the shape of the sea floor
Explain diffraction limited resolution.
The aperture diameter size determines the footprint size. There is destructive interference on the sides which limits the footprint.
what is the angular resolution equation?
angular resolution = (1.22*wavelength )/ aperture diameters
What is the resolution of satellite RADAR?
10s of Kms (microwaves sent out with 10s of cm wavelengths)
What is the resolution of Lidar?
10s of meters, the wavelength is hundreds of nanometers
What is the advantage of side looking radar?
You can differentiate the sides of things and improves range resolution
What footprint does side looking radar leave?
An ellipsoidal footprint
How does side looking radar work?
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.
What returns to the sattelite when the surface is completely flat?
Nothing
What kind of surface reflects the more signal back to the satellite?
A rough surface
What situation leads to total backscatter?
corner reflector (conainer ships)
How does RADAR imagery detect oil spills?
Tit can pick up a change in surface tension which affects the reflection
What is InSAR
Interferometric Synthetic Aperture Radar
What is an amplitude image made up of?
backscatter energy
What does the phase image look like?
random pixels, no pattern visible in level 1
what is the single look complex?
the amplitude and phase before they’re combined
We can’t measure the number of wavelengths from the satellite to the target and back, what do we do?
we look at the phase difference?
how is phase measured?
in a 2 pi cycle
What did the 2000 SRTM mission do and how long did it take?
the Shuttle Radar Topogrpahy Mission mapped topography within +-60° latitude in 11 days using a 60m baseline
What does InSAR do?
It calculates the phase shift resulting from ground movement following an earthquake
What is coregistration?
Its the aligning of the image prior and post earthquake
What is the required accuracy for co- registration?
1/8 of a pixel to meet the requirement of interferometry
What are the requirements for co registration?
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
What calculation is done to show ground movement?
phase A - phase B
How do you determine the deformation?
counting fringes
What does phase unwrapping do?
it smooths out the interferogram by adding segments, check graph in one note
What happens when the difference between two pixels in more than 2 pi?
the deformation is too drastic and the interferogram becomes incoherent
How do you calculate average ground velocity using InSAR?
Stacking interferograms. You add up interferograms and divide by total time
InSAR can measure very slow deformation but what can impact the precision of the readings
Atmospheric noise
What is the signal to noise ratio?
look up
What can be derived from the interferogram network?
the velocity (ground displacement over time)
Why does pointing angle change between ascending and descending line of sight velocity maps?
because the earth is rotating as the satellite passes
What does interseismic strain rate inform?
It informs seismic hazard
What can be an issue in interpreting vertical InSAR velocities?
permafrost deformation/ melting, groundwater extraction for farming, blocked drainage, mining
what is blocked drainage and how does it look in an interferometry map?
it’s the uplift from water trying to exit the basin under a mountain
What will future satellites provide?
a 3rd line of sight, providing a norht/ south deformation, allowing us to measure deformation in 3D
What will the BIOMASS mission provide?
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)
