Vaisala RVP900 - Table 47 Algorithm Results for +26 Db Interference

3.14%
. .
1.06%
. .
0.51%
. .
0.54%
. .
2.53%
. .
0.85%
. .
0.33%
. .
0.35%
. .
2.07%
. .
0.67%
. .
0.22%
. .
0.23%
. .
1.70%
. .
0.54%
. .
0.14%
. .
0.15%
. .
1.21%
. .
0.35%
. .
0.06%
. .
0.06%
. .
0.65%
. .
0.14%
. .
0.01%
. .
0.01%
. .
It is important to minimize both types of errors. If too much interference is missed, then the
filter does not do an adequate job of cleaning up the received signal. If the false alarm rate is
too high, then background damage is done at all times and the overall signal quality
(especially sub-clutter visibility) may be compromised. Try to keep the false alarm rate fairly
low, perhaps below 1%; and let the missed percentage fall where it may.
The following table shows the results obtained if the interference dominates by 26 dB. To
summarize the numerical results in the table:
• The Missed rates of Alg.1 and Alg.2 are identical, but the False rate of Alg.1 is
much higher. Alg.1 does not perform as well for additive interference, but it is
included in the suite for historical reasons.
• The Missed error rate for Alg.3 is nearly identical to that of Alg.2, but Alg.3 has a
significantly lower false alarm rate. This is because of the somewhat improved statistics
that result when the linear mean of P
n-2
and P
n-1
is used in the second comparison,
rather than just P
n-1
alone. We recommend that Alg.3 generally be chosen in
preference to the other two.
• Alg.3 can be further tuned by allowing the two constants to
dier. For example, by
raising C
1
slightly above C
2
(fourth column), we can trade
o a decrease in the
Missed rate for an increase in the False rate. Lowering C
1
would have the opposite
eect.
Optimum tuning depends on the type of interference you are trying to remove. In the
previous example, where the interfering signal is only 16 dB stronger than the weather, there
was a close
trade-o between the Missed and False error rates.
Table 47 Algorithm Results for +26 dB Interference
C1,C2 Alg.1 Missed/
False
Alg.2 Missed/
False
Alg.3 Missed/
False
Alg.3, C2+=5 dB
Missed/False
6.0dB 17.8% 10.75% 17.8% 3.95% 17.8% 3.44% 17.8% 0.34%
8.0dB 9.9% 6.48% 9.9% 2.31% 9.9% 1.68% 9.9% 0.15%
9.0dB 7.4% 4.99% 7.4% 1.75% 7.4% 1.14% 7.4% 0.10%
10.0dB 5.9% 3.91% 5.9% 1.36% 5.9% 0.76% 5.9% 0.06%
11.0dB 4.8% 3.06% 4.8% 1.06% 4.8% 0.50% 4.8% 0.04%
12.0dB 3.2% 2.37% 3.2% 0.83% 3.2% 0.33% 3.2% 0.03%
RVP900 User Guide M211322EN-J
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