Suppose that the
and
samples are coming from two signal generators installed on a
dual-receiver system, and that only the B-Channel is AM modulated so that:
=
,
,
,
,
... ,
=
, 0,
, 0,
...
Then the above estimator reduces to:
=
1
2
2
×
1
2
2
= 07.07
A simple way to create these data is to set the A-Channel siggen for 95% AM depth, and use
a sinusoidal modulation source of, perhaps, 400 Hz. We do not choose 100% depth because
we would lose the burst phase reference when the amplitude became smallest. The 26 dB
reduction in S
B
is a close enough approximation to zero in the above formula.
If we now observe the two receive channels with the RVP900 at a PRF of 800Hz, we see the
RHOAB terms varying with range; reaching a high value of 1.00, and a low value of 0.707.
The plots are nearly stationary on the Ascope screen because the PRF is almost precisely
twice the modulation rate (though they are free-running relative to each other).
Adjusting the amplitude of either signal generator is not
aect the p terms, but it does have
an interesting
eect on SQI. If (T,Z,V,W) are computed from both channels combined, then
the SQI is:
=
2
2
+
1
2
2
If we solve this equation for SQI=0.5 we find that the individual S
A
terms must have twice
the power of the individual S
B
terms. This can be checked by adjusting either signal
generator until the minimum plotted SQI is 0.5, and then verifying that the average H and V
powers are identical; or, equivalently, that ZDR, LDRH and LDRV are 0.
The linear FM ramp (see 7.10.1 Linear Ramp of Velocity with Range (page 231)) can also be
used as a test of RHOAB in a dual-receiver system. With one siggen modulated and the
other
fixed, one receive channel appears to rotate relative to the other. If the FM modulation
is such that 1/N of a full revolution occurs per pulse at a given range, then if the sample size
is N pulses we observe RHOAB = 0 at that range. The plot of RHOAB shows a characteristic
sin (x)/x behavior as a function of range.
Chapter 7 – Processing Algorithms
233
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