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