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INVERSION OF SYNTHETIC APERTUR,E R,ADAR (SAR) - MSpace ...

INVERSION OF SYNTHETIC APERTUR,E R,ADAR (SAR) - MSpace ...

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olbital <strong>SAR</strong> is given by<br />

Ion = -'#{t<br />

-rä<br />

2<br />

++þ-sin2xsil'?ry')<br />

(cosiy'{sino sin¡ tanø sinry')<br />

Ø"' '<br />

. a! ,l<br />

f :i sin ¡ siu ry' tan a (cos ry' sirr o<br />

- sin þ cos X cos a) j<br />

Q.44)<br />

(Raney [91]). It is noted that the Doppler frequency late clepends only on<br />

the lelative location of a scatterer with respect to the sensor.<br />

3,2.3 Conventional Digital <strong>SAR</strong>, Processors<br />

Ear'ly works on cligital <strong>SAR</strong> processing tecliniclues can be founcl in Blorvn<br />

et aL ll3l,I(iLk [55], ancl Maltinson [74].<br />

These authors did not yet provicle<br />

a full-scale processing scheme for cligital <strong>SAR</strong> irnage reconstruction, Mole<br />

cletailecl and complete digital <strong>SAR</strong> processing schenes wele discussed by Wu<br />

[109], van de Lindt [60], ancl Bennett and Cumming [6] [7]. The plincipal<br />

stlategy of tliese algorithms is such that the <strong>SAR</strong> irnagely can be leconstlucted<br />

by two sequential corlelations of tlle leturn signal with the range refelence<br />

function fir'st ancl then by the azimuth reference function second, thlough<br />

fast correlation approach using the one-dirnensional fast Fourier tlansfolrn<br />

(FFT). The florv chart for the algolithrn is shorvn in Figu::e 3.9.<br />

The mathematical moclel of tìre <strong>SAR</strong> letuln signal may help the algolithrn<br />

to be better undelstood. A <strong>SAR</strong> system generally transmits ancl I'eceives<br />

signal using the same antenna. Duling the tlansnission over a pulse cluration<br />

?, the fi'ecluency is linearly moclulated or "chirped", rvhile the frequency<br />

56

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