Co-Registration of SACo-Registration of SAR Image Pairs for InteR Image Pairs for Inte

rferometryrferometry

Current Progress Current Progress && Preliminary Results Preliminary Results

An InSAR Co-registration ModuleAn InSAR Co-registration Module “PurSAR” “PurSAR” InSAR co-registrationInSAR co-registration Coherence EvaluationCoherence Evaluation Interferogram GenerationInterferogram Generation DEM Processed by ASF SAR Processor + “PurSAR” DEM Processed by ASF SAR Processor + “PurSAR”

+ ERDAS+ ERDAS Experiments & AnalysisExperiments & Analysis

Co-registration ModuleCo-registration Module “PurSAR”“PurSAR”

Coarse co-registrationCoarse co-registration Cross-correlation by FFTCross-correlation by FFT Finding coarse tie pointsFinding coarse tie points Coarse image shiftCoarse image shift

Fine co-registrationFine co-registration Finding and filtering sub-pixel tie Finding and filtering sub-pixel tie

pointspoints 4 and 6 parameters transformation4 and 6 parameters transformation Nearest neighbor, linear, cubic, Nearest neighbor, linear, cubic,

and SINC interpolatorsand SINC interpolators Coherence computationCoherence computation Interferogram generationInterferogram generation

Coarse co-registrationCoarse co-registration

Defining the gridsDefining the grids Cross-correlation computationCross-correlation computation Filtering cross-correlation peaks by Filtering cross-correlation peaks by

peak-to-rms ratiopeak-to-rms ratio Finding the matching points and Finding the matching points and

discarding the outliersdiscarding the outliers Determining the x and y shiftsDetermining the x and y shifts Shift of the slave imageShift of the slave image

Fine co-registrationFine co-registration Defining the gridsDefining the grids SINC up-sampling the small windows surrounding SINC up-sampling the small windows surrounding

the grid pointsthe grid points Cross-correlation computationCross-correlation computation Filtering cross-correlation peaks by peak-to-rms ratioFiltering cross-correlation peaks by peak-to-rms ratio Finding the matching points and discarding the Finding the matching points and discarding the

outliersoutliers Set 4-par & 6-par transformation equations by least Set 4-par & 6-par transformation equations by least

squaresquare Re-sampling the slave image by nearest neighbor, Re-sampling the slave image by nearest neighbor,

linear, cubic, and SINC interpolatorslinear, cubic, and SINC interpolators SINC interpolators: normalized, windowed, and doppler SINC interpolators: normalized, windowed, and doppler

centroid shiftedcentroid shifted

Coherence, Interferogram, Coherence, Interferogram, and DEMand DEM

Coherence evaluationCoherence evaluation Coherence image computationCoherence image computation Coherence statistics: average, histogram, etcCoherence statistics: average, histogram, etc Coherence table: re-sampling algorithms vs. Coherence table: re-sampling algorithms vs.

coherence magnitudecoherence magnitude Coherence comparison with ASF SAR ProcessorCoherence comparison with ASF SAR Processor

Interferogram computationInterferogram computation DEM generationDEM generation

Importing co-registered SAR image pair into Importing co-registered SAR image pair into ERDASERDAS

Type in the orbit informationType in the orbit information Processing the SAR images into DEM in ERDAS Processing the SAR images into DEM in ERDAS

RadarRadar DEM evaluationDEM evaluation

ExperimentsExperiments

Comparison among airborne RTV SAR Comparison among airborne RTV SAR DEM, LIDAR and Aerial DEMDEM, LIDAR and Aerial DEM

ERS InSAR processing and coherence ERS InSAR processing and coherence evaluationevaluation

Patch 2-AR-RoofPatch 2-AR-Roof

5.07095.071

5.0711

x 105

4.4753

4.4753

4.4753

4.4753

x 106

160

165

170

175

X/Easting (Meter)

Aerial DEM: 2-AR-Roof

Y/Northing (Meter)

Elli

psoi

dal H

eigh

t (M

eter

)

5.07095.071

5.0711

x 105

4.4753

4.4753

4.4753

4.4753

x 106

160

165

170

175

X/Easting (Meter)

InfSAR DEM: 2-AR-Roof

Y/Northing (Meter)

Elli

psoi

dal H

eigh

t (M

eter

)

Armory (Building/Roof)Armory (Building/Roof)

Armory-EW Armory-EW (Building/Roof)(Building/Roof)

5.0706 5.0708 5.071 5.0712 5.0714

x 105

130

140

150

160

170

180

190

200

Profile Comparison: 1-AR-EW-Roof

X/West-East (Y=4475290, UTM, Meters)

Elli

psoi

dal H

eig

ht (

Met

er)

AerialLidarInSAR

Armory-NS Armory-NS (Building/Roof)(Building/Roof)

4.4752 4.4753 4.4753 4.4753 4.4753

x 106

130

140

150

160

170

180

190

200

Profile Comparison: 2-AR-NS-Roof

Y/South-North (X=507098, UTM, Meters)

Elli

psoi

dal H

eig

ht (

Met

er)

AerialLidarInSAR

ERS InSAR processing and cohERS InSAR processing and coherence evaluationerence evaluation

ERS ERS Data descriptionData description

InSAR pair: a.cpx (master) and InSAR pair: a.cpx (master) and b.cpx (slave)b.cpx (slave)

Location: Fairbanks, AlaskaLocation: Fairbanks, Alaska Size: 5000 rows and 1000 Size: 5000 rows and 1000

columns; cut from a standard columns; cut from a standard scene (about 25000x5000) scene (about 25000x5000)

Format: Single-look complexFormat: Single-look complex Processed by ASF SAR ProcessorProcessed by ASF SAR Processor The right image is only the The right image is only the

magnitude for a.cpxmagnitude for a.cpx

Coarse Co-registrationCoarse Co-registration Pair: a.cpx and b.cpxPair: a.cpx and b.cpx Grids: 5x3 = 15 pointsGrids: 5x3 = 15 points Peak-to-RMS Ratio = Peak-to-RMS Ratio = 0.004 Searching window size = 256 Use only magnitude as input for cross-Use only magnitude as input for cross-

correlation computationcorrelation computation All 15 points have good peaks and no All 15 points have good peaks and no

outlieroutlier Shifts: 2 in x-direction (range); 1 in y-Shifts: 2 in x-direction (range); 1 in y-

direction (azimuth)direction (azimuth) b.cpx b.cpx b_shift.cpx b_shift.cpx

15 Pairs of Matching 15 Pairs of Matching PointsPoints

Cross-correlation Peak Cross-correlation Peak for Point (700, 300)for Point (700, 300)

Fine Co-registrationFine Co-registration Pair: a.cpx and b_shift.cpxPair: a.cpx and b_shift.cpx Grids: 5x5 = 25 points for better Grids: 5x5 = 25 points for better

performanceperformance Up-sampling ratio = 11Up-sampling ratio = 11 Up-sampling interpolator: SINCUp-sampling interpolator: SINC Peak-to-RMS Ratio = Peak-to-RMS Ratio = 0.003 Searching window size = 33 before up-

sampling Cross-correlation with only magnitudeCross-correlation with only magnitude Cross-correlation with complex dataCross-correlation with complex data

Cross-correlation with Only Cross-correlation with Only Magnitude ---- Matching Magnitude ---- Matching

PointsPoints

Cross-correlation with Only Cross-correlation with Only Magnitude ---- Point (500, Magnitude ---- Point (500,

100)100)

Cross-correlation Section Cross-correlation Section with Only Magnitude ---- with Only Magnitude ----

Point (500, 100)Point (500, 100)

Cross-correlation with Only Cross-correlation with Only MagnitudeMagnitude

All 25 points have good peaksAll 25 points have good peaks A beautiful A beautiful sub-pixel sub-pixel peak for Point peak for Point

(500, 100)(500, 100) Azimuth direction sectionAzimuth direction section

Solid linesSolid lines Up-sampled cross-correlationUp-sampled cross-correlation 1/111/11thth sub-pixel matching accuracy sub-pixel matching accuracy

Dash lines Dash lines Original pixel cross-correlationOriginal pixel cross-correlation Mostly zero after coarse co-registrationMostly zero after coarse co-registration

Cross-correlation with Cross-correlation with Complex Data ---- Point Complex Data ---- Point

(500, 100)(500, 100)

Cross-correlation with Cross-correlation with Complex DataComplex Data

Only 3 points passed the filterOnly 3 points passed the filter No obvious single peakNo obvious single peak Noise added by including phase dataNoise added by including phase data So better to use only magnitude for sub-So better to use only magnitude for sub-

pixel co-registration for this SAR pairpixel co-registration for this SAR pair; but ; but not alwaysnot always

6-par Transformation6-par Transformation

100 200 300 400 500 600 700 800 900 1000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Delta: Shift

Image Column (pixel)

Imag

e R

ow (

pixe

l)

RightLeft

Discarding the OutliersDiscarding the Outliers

100 200 300 400 500 600 700 800 900 1000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Delta: Shift

Image Column (pixel)

Imag

e R

ow (

pixe

l)

RightLeft

6-par Transformation6-par Transformation & & Discarding the OutliersDiscarding the Outliers

5 outliers were 5 outliers were filtered outfiltered out

6-parameter 6-parameter transformation transformation equationsequations

Coefficients for y are Coefficients for y are much less significant much less significant than those for xthan those for x

So 4-parameter So 4-parameter transformation is OKtransformation is OK

NofPoints =

25

X = 1.000267*x + 0.000016*y + 0.117293StDev of X = 0.046124

Y = -0.000279*x + 1.000002*y + 0.454738StDev of Y = 0.047559

NofPoints =

20

4-par Transformation4-par Transformation

100 200 300 400 500 600 700 800 900 1000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Delta: Shift

Image Column (pixel)

Imag

e R

ow (

pixe

l)

RightLeft

Discarding the OutliersDiscarding the Outliers

100 200 300 400 500 600 700 800 900 1000

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Delta: Shift

Image Column (pixel)

Imag

e R

ow (

pixe

l)

RightLeft

4-par Transformation4-par Transformation & & Discarding the OutliersDiscarding the Outliers

NofPoints = 25

X = x + 0.000229*x + 0.187576StDev of X = 0.046135

Y = y + -0.000274*x + 0.453660StDev of Y = 0.047165

NofPoints = 20

2D Separable SINC 2D Separable SINC FunctionFunction

Re-samplingRe-sampling

Re-sampling the slave image b_shift.cpx Re-sampling the slave image b_shift.cpx by nearest neighbor, linear, cubic, and by nearest neighbor, linear, cubic, and SINC interpolatorsSINC interpolators

b_shift.cpx b_shift.cpx b_nearest_4par.cpxb_nearest_4par.cpx b_linear_4par.cpxb_linear_4par.cpx b_cubic_4par.cpx (bicubic)b_cubic_4par.cpx (bicubic) b_sinc2_4par.cpx (SINC length = 2)b_sinc2_4par.cpx (SINC length = 2) …… b_sinc20_4par.cpx (SINC length = 20)b_sinc20_4par.cpx (SINC length = 20)

Coherence ImageCoherence Image---- a.cpx vs. b.cpx---- a.cpx vs. b.cpx

Coherence ImageCoherence Image---- a.cpx vs. b_shift.cpx---- a.cpx vs. b_shift.cpx

Coherence ImageCoherence Image---- a.cpx vs. ---- a.cpx vs.

b_sinc4_4par.cpxb_sinc4_4par.cpx

Coherence Statistics (I)Coherence Statistics (I)

Image Pair for Coherence Image Pair for Coherence ComputationComputation

Average Average CoherencCoherencee

a.cpx + b_corr.cpx (Co-a.cpx + b_corr.cpx (Co-registered and Re-sampled by registered and Re-sampled by ASF SAR processor)ASF SAR processor)

0.6950.695

a.cpx + b.cpx (before any co-a.cpx + b.cpx (before any co-registration)registration)

0.1910.191

a.cpx + b_shift.cpx (after coarse)a.cpx + b_shift.cpx (after coarse) 0.6130.613

a.cpx + b_nearest_4par.cpxa.cpx + b_nearest_4par.cpx 0.6130.613

a.cpx + b_linear_4par.cpxa.cpx + b_linear_4par.cpx 0.6610.661

a.cpx + b_cubic_4par.cpx a.cpx + b_cubic_4par.cpx (bicubic)(bicubic)

0.6800.680

Coherence Statistics (II)Coherence Statistics (II)

Image Pair for Coherence Image Pair for Coherence ComputationComputation

Average Average CoherencCoherencee

a.cpx + b_sinc2_4par.cpxa.cpx + b_sinc2_4par.cpx 0.6910.691

a.cpx + b_sinc4_4par.cpxa.cpx + b_sinc4_4par.cpx 0.7010.701

a.cpx + b_sinc6_4par.cpxa.cpx + b_sinc6_4par.cpx 0.7010.701

a.cpx + b_sinc8_4par.cpxa.cpx + b_sinc8_4par.cpx 0.7000.700

a.cpx + b_sinc10_4par.cpxa.cpx + b_sinc10_4par.cpx 0.6990.699

a.cpx + b_sinc14_4par.cpxa.cpx + b_sinc14_4par.cpx 0.6990.699

a.cpx + b_sinc20_4par.cpxa.cpx + b_sinc20_4par.cpx 0.6960.696

Coherence AnalysisCoherence Analysis ASF SAR Processor uses 4 or 6-point cubic ASF SAR Processor uses 4 or 6-point cubic

convolution for re-samplingconvolution for re-sampling It is better than nearest neighbor, linear, and It is better than nearest neighbor, linear, and

bicubic interpolationbicubic interpolation However, a 4-point SINC interpolator gives the However, a 4-point SINC interpolator gives the

better coherence than itbetter coherence than it The speed of computer has increased a lot, The speed of computer has increased a lot,

and the price has lowered significantly and the price has lowered significantly during the last 10 years; So SINC during the last 10 years; So SINC interpolation can be used practicallyinterpolation can be used practically

The longer SINC is not always better for The longer SINC is not always better for interpolation, due to the noiseinterpolation, due to the noise

InterferogramInterferogram-------- a.cpx and a.cpx and

b_sinc4_4par.cpxb_sinc4_4par.cpx

Single look Multi look

Interferogram Interferogram ---- S---- Spherical pherical EEarth arth

CCorrectionorrection

Interferogram Interferogram ---- Phase Unwrapped---- Phase Unwrapped

InSAR DEMInSAR DEM in Slant Range in Slant Range

Final Final InSAR DEMInSAR DEM