Page 53 - Introduction to Information Optics

38 1. Entropy Information and Optics

Broad Gaussian
Narrow Gaussian
Envelope /
Pulse

(a)

Contours of |%|

Single Pulse
Train of Pulses

(b)
Fig. 1.13. (a) A Gaussian pulse-train, (b) Ambiguity diagram of (a).

Note that in actual application, we are not interested in resolving all the ranges
of the target, for which the redundant parts of the ambiguity diagram remote
from the origin have no practical usage. For example, a target 10 miles away
should not be confused with one 1010 miles away. In practice, we may draw a
rectangular region around the origin of the (T, v) coordinate plane to discrimi-
nate the ambiguity outside the region. Therefore, we see that the pulse train
example will be a more acceptable waveform for range and (radial) velocity
discrimination, as compared with the ambiguity distribution obtained from a
single pulse. However, when interpreting the ambiguity diagram, one should
remember that t and v do not represent the actual range and (radial) velocity,
but rather the difference between the ranges and velocities of any two targets
that need to be resolved.