Unit 9 Flashcards
Define passive microwave
sensors detect emitted terrestrial radiation
define radar alimetry
ranging sensors that measure elevation of land or water surfaces
define radar scatterometers
microwave radiometers that measure scattered energy off of land and water surfaces
microwave remote sensing that includes imaging and ranging sensors that detect intensity and phase of backscattered energy
synthetic aperture radar (SAR)
How far does the microwave region range? Why does this matter?
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.
What is the major benefit of microwave remote sensing?
Since larger than molecules we can see through clouds as they don’t interact = spaceborne remote sensing works great
Are microwave remote sensors (ex. Radar) active or passive and why?
Active, because the wavelength of the sun is too small to see the reflected energy
What is a major application of Radar remote sensing (such as SAR)?
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
How is SAR similar to LIDAR but different?
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
What are some of the downsides to the side-looking aspect of SAR?
causes foreshortening, layover, and shadowing
What is foreshortening in regards to SAR?
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
what is layover in regards to SAR?
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
What is the term in SAR for when energy does not reach an area due to obstruction such as a hill?
Shadowing
What are the three backscatter mechanisms?
Surface scattering, specular reflection, and double-bounce back scattering
*review each
How does the x-band, c-band, and l-band differ when looking at a forest?
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
What is polarization of light?
The orientation of the light in space
What polarization does sunlight have?
it is randomly polarized
How does polarization related to active radar systems?
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
What is the different between dual polarized and quadrature polarized systems?
Dual transmit either V or H and receive both, Quadrature transmit both V and H and receive both
What is an example of a dual, quadrature, and circularly polarized system
Sentinel-1
RADARSAT-2
RADARSAT Constellation Mission
What is the downside of quadrature polarized systems? And what would be the solution
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
What backscatter mechanisms stand out in which polarization?
single or double bounce scatter stand out in VV because the horizontal is week in these mechanisms
What would have a higher horizontal backscatter?
dense clustered vegetation like canopies = forests have a greater H than agricultural areas (volumetric scattering)
This leads to increased depolarization
What is polarimetric decomposition?
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
