MO3.L09.2 - BISTATIC SAR BASED ON TERRASAR-X AND GROUND BASED RECEIVERS

Dept. Signal Theory & Communications RemoteSensing Laboratory (RSLab) 1

BISTATIC SAR BASED ON TERRASAR-X AND BISTATIC SAR BASED ON TERRASAR-X AND GROUND BASED RECEIVERSGROUND BASED RECEIVERS

A.Broquetas, M.Fortes, M.A.Siddique, S.Duque, J.C.Merlano, P.López-Dekker, J.J.Mallorquí, A.Aguasca

Remote Sensing Laboratory (RSLab)

Universitat Politècnica de Catalunya, Barcelona

Dept. Signal Theory & Communications RemoteSensing Laboratory (RSLab) 2

Introduction: Fixed receivers bistatic SAR

SABRINA-X Receiver design & implementation

Bistatic SAR Processing

Results

Conclusions

ContentsContents

2005

2006

2007

2008

2009

2010

• Firs

t BiS

AR Imag

es

• Sing

le-pa

ss fri

nges

.

• Sing

le-pa

ss DEM

• Rep

eat-p

ass

InSAR

• Firs

t Exp

erim

ents

(C-B

and)

• ATI,

Tomog

. , X-B

and

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IntroductionIntroduction : Fixed receivers bistatic SAR : Fixed receivers bistatic SAR

WHY?•Wide angle bistatic scattering understanding•SAR raw data in flexible RX configurations: InSAR, PolSAR, Tomography•Training covering the whole SAR chain: systems/processing/new applications

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Bistatic SAR Spatial ResolutionBistatic SAR Spatial Resolution

Bistatic Resolution:

For the monostatic case, the ground range resolution depends inversely to the sine of the transmitter local incidence angle.

For the bistatic case, the ground range resolution depends inversely to both sines of the transmitter and the receiver local incidence angles.

In the bistatic case, the azimuth resolution is slightly worse than monostatic, due to the one-way path

TX

RX

α

( ) ( )( )αθαθ −+−⋅∆=∆

rtcbistaticg f

cr

sinsin

( )αθ −⋅∆⋅=∆

tcmonostaticg f

cr

sin2

2monostatic

lz∆ =

2bistatic

lz∆ =rθ

tθ

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SABRINA-X: Channel Block DiagramSABRINA-X: Channel Block Diagram

Homodyne configuration for simplicity and low cost/size/weight/consumption

Initially designed with 2 channels, now 3, channel 4 is being implemented

Multiple channels needed for Interferometry, Polarimetry, MSAR

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SABRINA-X: L.O. SynthesizerSABRINA-X: L.O. Synthesizer

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SABRINA-X: Subsystem design & development (I)SABRINA-X: Subsystem design & development (I)

LNA: 9 -18 GHz, G = 19 dB, NF = 2 dB

RF Filter: 9.5-9.8 GHz, I.Loss = 3 dB

Horn Antennas G = 18 dB

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SABRINA-X: Subsystem design & development (II)SABRINA-X: Subsystem design & development (II)

I/Q DET.: RF 7.1-13.5 GHz, IF:DC-3.5 GHz, CL= 9 dB

BB Amp. & LP Filter G =16.5 dB

RF Amp. 6.5 a 13.5 GHz G=14 dB NF= 4.5dB

1/4 Freq. Synthesizer X4 Freq. Multiplier

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4 Acquisition Modes: I/Q BB: 4 Acquisition Modes: I/Q BB: 2 A/D x RF channel. Fs = 200/100 MS/s 2 A/D x RF channel. Fs = 200/100 MS/s

Bandwidth retained < Fs MHz

200 Ms/s example with low-pass filter 70 MHz cut-off

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4 Acquisition Modes: Low-IF : 4 Acquisition Modes: Low-IF : 1 A/D x RF Channel. Fs = 200/100 MS/s 1 A/D x RF Channel. Fs = 200/100 MS/s

100 Ms/s example with low-pass filter 48.5 MHz cut-off

Bandwidth retained < 1/2 Fs MHz

Dept. Signal Theory & Communications RemoteSensing Laboratory (RSLab)

Campaign Set-upCampaign Set-up

Antennas receiving Scattered signals

Antenna receiving Direct signal

SABRINA-X

11

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Acquired Data & SynchronizationAcquired Data & Synchronization

Pulse-trains

Illumination envelopes • Receiver synchronization offline: preprocessing• Illumination envelope, coarse PRF and pulse replica are

obtained from direct illumination channel • From range compressed pulses accurate time

alignment of both direct and scattered signals is achieved

• The frequency offset between TSX and SABRINA is estimated from the pulse to pulse phase change

• Azimuth focusing is based on Backprojection

Direct + scattered Spectrogram

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Range compression with Chirp replica and receiver equalizationRange compression with Chirp replica and receiver equalization

Direct pulse compression evaluation Green: compression with linear FM chirpBlue: compression with chirp replica &RX H(f) equalization

Received spectrum Receiver H(f) Equalized Receiver H’(f)

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Bistatic SAR ImagesBistatic SAR Images

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Geocoded SAR ImageGeocoded SAR Image

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θr

Bn,r

A1

A2

Rr

θt

Rt

“Back”- scattering “Forward”- scattering

θt

Rt

Bistatic InSARBistatic InSAR

Acquisition scheme:

As in the monostatic case, the information resides in the difference of interferometric phase among nearby points.

( )

⋅

⋅∆⋅=∆Ψrr

rnABAB R

Bh

θλπ

sin

2 ,

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Preliminary geocoded InterferogramPreliminary geocoded Interferogram

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Geocoded Interferogram with low resolution DEM compensation Geocoded Interferogram with low resolution DEM compensation

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Geocoded reference imageGeocoded reference image

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ConclusionsConclusions

Bistatic SAR with fixed ground receivers allows to develop affordable complete SAR chains suitable for hands-on SAR training and multichannel SAR research

A multichannel X-Band SAR receiver has been designed by undergraduate students from low cost COTS monolithic devices

First results on Barcelona harbor using TSX illumination has shown the importance of acquiring clean direct channel replica and channels H(f) calibration/equalization for accurate range compression and InSAR

Metallic containers and ships produce very bright scattering centers even at wide bistatic angles

The cost of high speed digitizers is presently the main bottle-neck for budget multichannel operation. A PRF trigger is under development for longer acquisition at highest sampling rate