
The algorithm for calculating CCOR depends on whether the optional
R
2
autocorrelation lag
is computed.
7.4.7.1 R0, R1 Clutter Correction
In this case CCOR is estimated from,
����
���
= 10log
�
0
�
0
= 10log
� + �
� + � + � = 10log
1 +
1
���
��� + 1 +
1
���
Here, the expression is strictly valid only when the signal-to-noise ratio (
SNR=S/N
) is large.
When the 2-lag approach is used, the clutter corrections are not as accurate for weak
weather signals. However, the error is typically less than 3 dB.
7.4.7.2 R0, R1 Clutter Correction Using Clutter Signal and Noise Power
Calculations
In this case there is enough information to compute the clutter signal and noise power
independently. The algorithm for CCOR is:
����
���
= 10log
�
� + � = 10log
1
��� + 1
The clutter power is computed from:
� = �
0
− �
0
= � + � + � − � + �
The signal power
S
is then computed from:
� = �
1
exp �
2
�
2
2
W
is the width that has been previously calculated. This approach yields more accurate
results for the clutter correction in the case of a low SNR.
7.4.8 Weather Signal Power (SIG Threshold)
The
SIG
parameter provides an estimate of the weather signal-to-noise ratio in dB for
thresholding.
The
SIG
calculation is different depending on the whether the optional
R
2
autocorrelation is
computed.
Table 53 SIG Calculation
Autocorrelation
Equation
Description
R
0
,
R
1
��� = 10log
�
0
− �
�
+ ����
Represents the SNR after the
removal of clutter.
The
CCOR
value is that described
for
R
0
,
R
1
Correction (CCOR threshold)
(page 205)
RVP900 User Guide
M211322EN-J
206
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