User's Manual Part 2

Processing Algorithms (draft)
RVP8 User’s Manual
April 2003
5–60
5.7.12 Thresholding of Polarization Parameters
The thresholding of polarization parameters by the processor eliminates bins with weak or
uncertain signals. Note that the thresholding can be disabled if it is desired to see all of the data
regardless of the data quality.
All of the polarization parameters are based on power ratios. The RVP8 requires that each power
term in a ratio pass a signal-to-noise test similar to the log power test. For example, there are up
to four different powers that can be calculated (alternating dual-channel case) so the tests for
each of these are:
t |s
hh
|
2
u
N
h
Ą uĄ N
thresh
t |s
hv
|
2
u
N
h
Ą uĄ N
thresh
t |s
vv
|
2
u
N
v
Ą uĄ N
thresh
t |s
vh
|
2
u
N
h
Ą uĄ N
thresh
where the linearized threshold that is input as the dB LOG threshold, i.e.,
N
thresh
Ą +Ą10
LOGthreshń10
For example, a valid LDRH requires both a valid S
hh
and a valid S
vh
. The parameters RHOH
and PHIH have the same requirement since they are the magnitude and phase of the
cross-correlation function which is based on S
hh
and S
vh
.
There are two exceptions:
ZDR
ZDR requires that both S
hh
and S
vv
pass the signal-to-noise tests noted above. However,
ZDR can be additionally thresholded by any of the other threshold parameters (LOG, SIG,
SQI, CSR) similar to a standard moment. See section 5.3 for a description of the standard
moment thresholding.
PHIDP for single channel alternating case
PHIDP requires that both S
hh
and S
vv
pass the signal-to-noise tests noted above. In the single
channel alternating case, PHIDP must also satisfy the additional test that the Doppler veloc-
ity at the range bin must be valid, i.e., not thresholded by its own criteria. This is because
the algorithm for PHIDP in this case essentially subtracts the phase change due to the Dop-
pler velocity. If the Doppler velocity is uncertain, the algorithm cannot produce reliable re-
sults.