There are a number of reasons of disturbance in the performance of the SAR system and degradation in the quality of SAR image. Some of the reasons are nonlinearities of the SAR subsystem that damage the ability of the system resolution. Noise is one frequently seen problem in SAR images whose major source is image acquisition. Other sources of noise introduction are the position of sensor and velocity errors that result in geometric distortion in the SAR image. Major occurring problems in the SAR image are discussed in Table 1.
Table 1 Real problems in SAR images
|
Real
effects on SAR
images (Problems) |
Major
sources |
|
Geometric distortion |
· Change
in position: movement variation and changes in platform attitude (high and
low frequencies) cause distortion due
to the platform of spaceborne or
airborne. · Rotation
of earth, topographic effect and curvature cause
distortion due to earth. · Deviation
in sensor mechanism and viewing geometry: panoramic effect causes distortion
due to the sensor. · Refraction
and turbulence cause distortion due to
the atmosphere. · Time-variations
or drift and clock synchronicity cause
distortion due to measuring instruments. |
|
System nonlinear effects |
· Amplitude
error and phase error degrades the system impulse response function (IRF). · Thermal
noise damages the dynamic range of the system. · Quantisation
error, bit error noise and system
nonlinearities damage the azimuth resolution and dynamic range of IRF. |
|
Range migration |
· Linear
drift because of elliptical orbit and earth rotation. · The appearance of hyperbola shaped
reflection as target move towards the synthetic aperture. · Curvature
depends on range compressed response
due to which SAR handles the two-dimensional
space-variant problem. · High
velocities of airplanes and satellite-borne SAR system. |
|
Speckle Noise effects |
· SAR
images are shaped by the constant interaction of the transmitted high-frequency radar waves with target areas.
This constant interaction causes random constructive and destructive nosiness
that result in salt and pepper noise
all over the image. This noise scatters all around the image and suffers from
the speckle noise effects and degrades the quality of the SAR image. It is a
granular pattern noise that inherently exists in the SAR image. · The existence of numerous elemental scatterers with an arbitrary
distribution within a resolution cell. |
Note: If you are taking help from the above work and also incorporating the above content in your research work, Kindly make sure you are citing the below papers.
- https://www.sciencedirect.com/science/article/pii/S2215098617314003
- https://www.sciencedirect.com/science/article/pii/S1319157817301106
- https://www.sciencedirect.com/science/article/pii/S1319157817303865
- https://link.springer.com/article/10.1007/s11831-021-09548-z
Reviewed by IPR
on
January 31, 2022
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