Graphics Programs Reference
In-Depth Information
R
()
R
' () 0
>
R
' () 0
<
R
'
=
0
time
t
1
t
c
t
2
Figure 12.6. Sketch of range versus time for a scatterer.
scatterer Doppler history
maximum Doppler
time
0
t
c
t
2
t
1
minimum Doppler
Figure 12.7. Point scatterer Doppler history.
In general, the radar maximum PRF, , must be low enough to avoid
range ambiguity. Alternatively, the minimum PRF, , must be high enough
to avoid Doppler ambiguity. SAR unambiguous range must be at least as wide
as the extent of a footprint. More precisely, since target returns from maximum
range due to the current pulse must be received by the radar before the next
pulse is transmitted, it follows that SAR unambiguous range is given by
f
r
max
f
r
min
R
u
=
R
max
R
min
(12.13)
An expression for unambiguous range was derived in
Chapter 1,
and is
repeated here as Eq. (12.14),
c
2
f
r
R
u
=
------
(12.14)
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