COMPARISON OF GEOMETRY-BASED DOPPLER COMPARISON OF GEOMETRY-BASED DOPPLER AMBIGUITY RESOLVER IN SQUINT SAR AMBIGUITY RESOLVER IN SQUINT SAR & & Wenchao Li Wenchao Li University of Electronic Science and Technology of University of Electronic Science and Technology of China China AN INDIRECT DOPPLER RATE ESTIMATION SCHEME AN INDIRECT DOPPLER RATE ESTIMATION SCHEME OF SAR IN LOW-CONTRAST SCENE OF SAR IN LOW-CONTRAST SCENE
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COMPARISON OF GEOMETRY-BASED DOPPLER AMBIGUITY RESOLVER IN SQUINT SAR &
COMPARISON OF GEOMETRY-BASED DOPPLER AMBIGUITY RESOLVER IN SQUINT SAR &. AN INDIRECT DOPPLER RATE ESTIMATION SCHEME OF SAR IN LOW -CONTRAST SCENE. Wenchao Li University of Electronic Science and Technology of China. Introduction. Synthetic Aperture Radar (SAR). - PowerPoint PPT Presentation
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COMPARISON OF GEOMETRY-BASED DOPPLER COMPARISON OF GEOMETRY-BASED DOPPLER
AMBIGUITY RESOLVER IN SQUINT SARAMBIGUITY RESOLVER IN SQUINT SAR
&&
Wenchao LiWenchao Li
University of Electronic Science and Technology of ChinaUniversity of Electronic Science and Technology of China
AN INDIRECT DOPPLER RATE ESTIMATION AN INDIRECT DOPPLER RATE ESTIMATION
SCHEME OF SAR IN LOW-CONTRAST SCENESCHEME OF SAR IN LOW-CONTRAST SCENE
IntroductionIntroduction
Synthetic Aperture Radar (SAR)
An important remote sensing tool.
• Monostatic SAR
• Bistatic SAR
• Stripmap SAR
• Scan SAR
• Spotlight SAR
• Side-looking SAR
• Squint-looking SAR
……
IntroductionIntroduction
Squint SAR
z
y
O
BR
v
x
P
Geometry model
Squint angle
IntroductionIntroduction
Squint SAR
2 22
0 0 00
cos( ) ( ) sin ( ) ( )
2 ( )
vR t R t v t t t t
R t
Range History:
The linear term is range walk
The quadratic term is range
curvature
IntroductionIntroduction
21( ) exp[ 2 ( )]
2dc drs t j f t f t
• Doppler centroid ( )
• Doppler rate ( )drfdcf
After range walk correction, the azimuth data can be modeled as a linear frequency modulated (LFM) signal,
Signal model
IntroductionIntroduction
In principle, it is possible to compute Doppler
parameter from prior information provided by GPS/INS,
but measurement uncertainties on the information will
limit the accuracy.
2 22 cosdr
vf
R
2sindc
vf
IntroductionIntroduction
An incorrect Doppler centroid • a loss of SNR;
• an increase in the azimuth ambiguity level;
• a shift in the location of the target; …...
Incorrect Doppler rate Correct Doppler rate
An incorrect Doppler rate would blur the image.
IntroductionIntroduction
Therefore, Doppler parameter Estimation from echo data is an essential procedure for high quality SAR processing
According to the fact that Doppler rate is inversely proportional to range,
It indicates that the Doppler rate in low- contrast scene can be estimated indirectly.
Range compressed data
Choose the range bin that contains bright line
Radon transform
Output the Doppler rate of the range bin
Wigner-Ville distribution
Fit the Doppler rate of the range bin in low-contrast scene
Range walk correction
Estimation Flowchart
Doppler rate in high-contrast scene is estimated first using Radon-Wigner transform, and then using the fact that Doppler rate is inversely proportional to range, Doppler rate in low-contrast scene is estimated indirectly.
ResultsResults
High Contrast Scene With Prominent Point
Time frequency analysis Radon transform
Low Contrast Scene
Without Prominent Point
Time frequency analysis Radon transform
ConclusionsConclusions
The geometry-based scheme can be used to resolve Doppler ambiguity of SAR with large migration.
The speed of improved Radon transform scheme and the iterative scheme is about ten times faster than conventional Radon transform scheme.
An indirect estimation scheme of Doppler rate for low contrast scene is developed.
The indirect scheme is effective, and it can reduce computation time greatly.
Thank you for your listening!Thank you for your listening!