Graphics Programs Reference
In-Depth Information
σ
0
where is the clutter scattering coefficient, is the azimuth resolution,
and Eq. (12.6) was used to replace the ground range resolution. The number of
coherently integrated pulses within an observation interval is
∆
A
g
f
r
L
v
nf
r
T
ob
=
=
-------
(12.29)
where is the synthetic aperture size. Using Eq. (12.26) in Eq. (12.29) and
rearranging terms yield
L
λ
Rf
r
2∆
A
g
v
----------------
n
=
csc
β
k
(12.30)
The radar average power over the observation interval is
P
av
=
(
P
t
⁄
B
)
f
r
(12.31)
The SNR for
n
coherently integrated pulses is then
P
t
G
2
λ
2
σ
4(
3
R
4
kT
0
BL
Loss
---------------------------------------------
(
SNR
)
n
=
nSNR
=
n
(12.32)
Substituting Eqs. (11.31), (11.30), and (11.28) into Eq. (12.32) and performing
some algebraic manipulations give the SAR radar equation,
P
av
G
2
λ
3
σ
0
4(
3
R
3
kT
0
L
Loss
∆
R
g
2
v
-----------------------------------------
----------
(
SNR
)
n
=
csc
β
k
(12.33)
Eq. (12.33) leads to the conclusion that in SAR systems the SNR is (1)
inversely proportional to the third power of range; (2) independent of azimuth
resolution; (3) function of the ground range resolution; (4) inversely propor-
tional to the velocity
v
; and (5) proportional to the third power of wavelength.
12.5. SAR Signal Processing
There are two signal processing techniques to sequentially produce a SAR
map or image; they are line-by-line processing and Doppler processing. The
concept of SAR line-by-line processing is as follows: Through the radar linear
motion a synthetic array is formed, where the elements of the current synthetic
array correspond to the position of the antenna transmissions during the last
observation interval. Azimuth resolution is obtained by forming narrow syn-
thetic beams through combinations of the last observation interval returns. Fine
range resolution is accomplished in real time by utilizing range gating and
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