Graphics Programs Reference
In-Depth Information
pulse compression. For each range bin and each of the transmitted pulses dur-
ing the last observation interval, the returns are recorded in a two-dimensional
array of data that is updated for every pulse. Denote the two-dimensional array
of data as
MAP
.
To further illustrate the concept of line-by-line processing, consider the case
where a map of size is to be produced, where is the number of azi-
muth cells and is the number of range bins. Hence, is of size
, where the columns refer to range bins, and the rows refer to azimuth
cells. For each transmitted pulse, the echoes from consecutive range bins are
recorded sequentially in the first row of . Once the first row is com-
pletely filled (i.e., returns from all range bins have been received), all data (in
all rows) are shifted downward one row before the next pulse is transmitted.
Thus, one row of is generated for every transmitted pulse. Consequently,
for the current observation interval, returns from the first transmitted pulse will
be located in the bottom row of
N
a
×
N
r
N
a
N
r
MAP
N
a
×
N
r
MAP
MAP
MAP
MAP
, and returns from the last transmitted
pulse will be in the first row of
.
In SAR Doppler processing, the array is updated once every pulses
so that a block of columns is generated simultaneously. In this case,
refers to the number of transmissions during an observation interval (i.e., size
of the synthetic array). From an antenna point of view, this is equivalent to
having
MAP
N
N
N
N
adjacent synthetic beams formed in parallel through electronic steer-
ing.
12.6. Side Looking SAR Doppler Processing
Consider the geometry shown in
Fig. 12.9,
and assume that the scatterer
C
i
is located within the range bin. The scatterer azimuth and elevation angles
are and , respectively. The scatterer elevation angle is assumed to be
equal to , the range bin elevation angle. This assumption is true if the
ground range resolution,
kth
µ
i
β
i
β
i
β
k
∆
R
g
, is small; otherwise,
β
i
=
β
k
+
ε
i
for some
small
ε
i
; in this chapter
ε
i
=
0
.
The normalized transmitted signal can be represented by
s
()
=
cos
(
2π
f
0
t
ξ
0
)
(12.34)
where
f
0
is the radar operating frequency, and
ξ
0
denotes the transmitter
phase. The returned radar signal from
C
i
is then equal to
s
i
(
t
µ
i
,
)
=
A
i
cos
[
2π
f
0
(
t
τ
(
t
µ
i
,
)
)
ξ
0
]
(12.35)
i
where is the round-trip delay to the scatterer, and includes scat-
terer strength, range attenuation, and antenna gain. The round-trip delay is
τ
i
(
t
µ
i
,
)
A
i
Search WWH ::
Custom Search