Vaisala RVP900, User Manual, Page: 235 / 484

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 affect the p terms, but it does have
an interesting effect 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