Microwave Remote Sensing - Part 1 Flashcards
one of the most exciting growth areas in environmental remote sensing
Factual statement
Identify the wavelength ranges that are used for microwave remote sensing
1 millimeter to 1 meter (or frequencies from 300 MHz to 300 GHz)
1 - 100 million nm
Provide examples of active/passive microwave RS sensors
passive:
DMSP, Nimbus, AMSR-E
active sensors have the distinct advantage of measuring a much stronger signal than emitted microwaves, and thus can have much finer spatial resolutions (similar to multispectral optical sensors )
Describe some advantages of microwave remote sensing in comparison to optical remote sensing - 3 things
- make other types of measurements that provide more information about Earth’s surface
- longer wavelengths interact very differently with Earth surfaces and the atmosphere than the shorter wavelengths - capture very different types of observations, in conditions not possible with optical sensors
- measure the intensity of microwave emittance and the polarity of the light
provide some examples of microwave-specific applications - 7 things
- used to characterize sea ice at the poles
- microwaves have a unique interaction with ice vs water that allows
these instruments to more easily distinguish between liquid and
frozen water - measure the diminishment of sea ice
- mapping the earth’s surface
- mapping oceans and ice sheets
- measure soil moisture
- flood mapping
microwave wavelengths
can also be expressed as frequencies - where this is relatively uncommon for the shorter wavelengths, a great deal of the material discussing microwaves uses frequencies instead of wavelengths
longer than “optical” wavelengths, and include the visible spectrum out into the near and shortwave infrared
one of the most interesting and useful aspects of microwave remote sensing is that…
these longer wavelengths are relatively unaffected by clouds and other atmospheric constituents
microwave remote sensing measures a quantity called the…
backscattering coefficient
bright and dark parts of the image have a very different meaning in microwave images compared to optical ones - …
need to rely on the physics to understand what they represent about Earth
the Earth, like all objects with a temperature above absolute zero does emit …
radiation, and some of this is in the microwave range
passive microwave sensors are limited in spatial resolution - because of the very low levels of …
microwave radiation that is being emitted from Earth’s surface - which limits their application to large phenomenon such as sea ice, or large-scale soil moisture
Passive microwave radiometers can measure …
either horizontally or vertically polarized intensity
active sensors can also switch the …
polarization of the transmitted radiation to be horizontal or vertical
you can make false color composite from different operational modes - …
creating a combination of vertical or horizontal transmissions with a combination of vertical or horizontal radiation emittance
define single-pol, dual-pol, and quad-pol systems
single-pol: A system that transmits and receives in only one polarization, that is: either HH or VV
dual-pol: One that transmits in a single polarization but can receive in either horizontal or vertical polarizations
quad-pol: can transmit and receive in either mode, and thus can make 4 different measurements: HH, HV, VV, and VH
The electrical and geometric properties of materials on Earth, as well as their configuration within the instantaneous field of view of the sensor, …
together determine how a microwave signal’s polarity is transformed
linearly oriented features, like buildings or sand dunes, …
randomly oriented objects, such as leaves in a tree canopy usually …
- tend to preserve the polarization
- have a depolarizing effect on the signal
backscatter intensity with regard to polarity
the HH or VV backscatter intensity will be large from a target such as a building, but lower from a tree canopy because the microwave radiation reflected from the building will preserve the horizontal or vertical polarization of the transmitted signal (features preserve the “coherence” of the signal), whereas a large portion of the returned intensity from the tree canopy would have changed polarity
