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4.10. However, in practice this is not possible for two reasons. First, in the
presence of noise we lack knowledge of the peak correlation value; and sec-
ond, targets in general will have different amplitudes.
Now consider the case of a coherent pulse train described in
Fig. 4.7.
For a
pulse train, range accuracy is still determined by the pulsewidth, in the same
manner as in the case of a single pulse, while Doppler accuracy is determined
by the train length. Thus, time and frequency measurements can be made inde-
pendently of each other. However, additional peaks appear in the ambiguity
diagram which may cause range and Doppler uncertainties (see Fig. 4.11).
frequency
frequency
time
time
high threshold value
low threshold value
Figure 4.10. Effect of threshold value on resolution.
frequency
1
---
T
f
ô
τ′
f
ô
=
1
⁄
(
N
1
)
T
time
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