7/31/2019 09a Sar Processing
1/40
Radar systems:
SARSynthetic Aperture Radar
7/31/2019 09a Sar Processing
2/40
What does SAR stand for?
S yntheticA pertureR adar
7/31/2019 09a Sar Processing
3/40
What is the output?
Output: a microwave imagesof the earth with:- Amplitude information- Phase information
Coherent image
Azimuth
RangeMain use:
Earth observation
7/31/2019 09a Sar Processing
4/40
Range imaging
Time measurement
Back to thefundamentals
7/31/2019 09a Sar Processing
5/40
Range imaging
7/31/2019 09a Sar Processing
6/40
Range imaging
Detection geometry
7/31/2019 09a Sar Processing
7/40
Range imaging
Near range
Far range
7/31/2019 09a Sar Processing
8/40
Range imaging
The radar looks in slant range
CRITICAL POWER BUDGET: only a limited amount of energy is backscattered
7/31/2019 09a Sar Processing
9/40
Range imagingRange resolution
Ideal pulse:- high peak power- duration t = 0
Real pulse:- low peak power- duration t > 0
ENERGY?
7/31/2019 09a Sar Processing
10/40
Range imaging
7/31/2019 09a Sar Processing
11/40
Range Imaging
Non discriminating
7/31/2019 09a Sar Processing
12/40
Range imaging
Range resolution uncertainty:
What we can do?
7/31/2019 09a Sar Processing
13/40
Range imaging
Chirp pulse: linear frequency modulation
7/31/2019 09a Sar Processing
14/40
Range imaging
At the receiver: Pulse compression
Cross-correlation between the transmitted and received signal
TxRx Rx
2 targets
7/31/2019 09a Sar Processing
15/40
Range imaging
7/31/2019 09a Sar Processing
16/40
Azimuth ImagingAzimuth resolution
7/31/2019 09a Sar Processing
17/40
Azimuth ImagingAzimuth resolution
Not acceptableSolutions?
7/31/2019 09a Sar Processing
18/40
Azimuth ImagingAzimuth resolution
IMPOSSIBLE
7/31/2019 09a Sar Processing
19/40
Azimuth ImagingAzimuth resolution
7/31/2019 09a Sar Processing
20/40
Azimuth ImagingAzimuth resolution improvement
Sensor target range variation! Doppler effect
7/31/2019 09a Sar Processing
21/40
Azimuth ImagingAzimuth resolution improvement
Sensor target range variation! Doppler effect
7/31/2019 09a Sar Processing
22/40
Azimuth ImagingAzimuth resolution improvement
Sensor target range variation: focalisation process
7/31/2019 09a Sar Processing
23/40
Azimuth ImagingAzimuth resolution improvement
A i h I i
7/31/2019 09a Sar Processing
24/40
Azimuth ImagingAzimuth resolution improvement
DistanceIndependent!!!Azimuth resolution
A i h I i
7/31/2019 09a Sar Processing
25/40
Azimuth ImagingAzimuth resolution improvement: arbitrary antenna size?
A i h I i
7/31/2019 09a Sar Processing
26/40
Azimuth ImagingDoppler analysis
Same spectrum in range!!!
~Synthetic chirp in azimuth!
I f i
7/31/2019 09a Sar Processing
27/40
Image formation
Coherent acquisition system: 1 pixel = I+Q (magnitude, phase)
Raw data
I f ti
7/31/2019 09a Sar Processing
28/40
Image formation
Single Look Complex image(in radar geometry)
I f ti
7/31/2019 09a Sar Processing
29/40
Image formation
SLC
-SingleLookC
ompleximage
U d t di SAR i
7/31/2019 09a Sar Processing
30/40
Understanding SAR imagesgeometry
Near range
Far range
Recall
U d t di SAR i
7/31/2019 09a Sar Processing
31/40
Understanding SAR imagegeometry
Image formation Geometric characteristics
Sar images are recorded in Slant-Range(SR).Slant-Range image shows unequal distances and widths betweenfeatures.
GR
SR
sin22 SR
HSRGR Hyperbolic correction
Ground range: image resampled in regular grid
U d t di SAR i
7/31/2019 09a Sar Processing
32/40
Understanding SAR imagegeometry
Foreshortening Points A, B and C areequally on the ground.However, the distancebetween B' and C' isshortened compared to A-
B, because the top of themountain is relatively closeto the SAR sensor .
This effect may be compensated during the geocoding process if aterrain model is available (compensated, not recovered)
U d t di SAR i
7/31/2019 09a Sar Processing
33/40
Understanding SAR imagegeometry
Layover
This effect is destructive superimposition of pixels
U d t di SAR i
7/31/2019 09a Sar Processing
34/40
Understanding SAR imagegeometry
Shadowing
Dark pixels in the imagesno signal
U d t di SAR i
7/31/2019 09a Sar Processing
35/40
Understanding SAR imagegeometry
Foreshortening vs layover vs shadowing
- layover >- foreshortening > 0, /2 -
Understanding SAR image
7/31/2019 09a Sar Processing
36/40
Understanding SAR imagegeometry
7/31/2019 09a Sar Processing
37/40
Geocoding, Radiometric Calibration andNormalization
- Transformation from radar geometry to a cartographic projection
- Radiometric calibration and normalization of SAR data
7/31/2019 09a Sar Processing
38/40
Geocoding
InputSlant rangegeometry
Resampling
OutputGround rangegeometry
Precise geocoding
Control pointsRefined orbital parametersSystem parameterDEM
Foreshortening effects can be corrected with the
availability of high resolution Digital Elevation
Model (DEM) data. Layover and Shadow areascan be calculated, but not corrected.
7/31/2019 09a Sar Processing
39/40
Radiometric Calibration
1) Correction of the antenna gain pattern
2) Correction for the range spread loss
3) Radiometric normalization(sensors,time, look angles)
Look Angle influence on Sar SignatureX : Range Y = radar backscatter
white : not normalized
red : normalized
Input: ERS2-scene, Canada
7/31/2019 09a Sar Processing
40/40
CalibrationScattering matrix
DLR Corner Reflectors
vv
Top Related