User's Manual Part 2

Processing Algorithms (draft)
RVP8 User’s Manual
April 2003
5–44
Noise Bias of Channel Power and Optional Correction
The average noise powers N
v
and N
h
are assumed to be receiver noise only. These bias the
autocorrelations at lag zero, i.e., the channel power measurements. Autocorrelations at lags 1 and
2 are not biased by noise. Cross channel correlations are also not biased by noise, assuming that
the noise in the two channels is independent (a good assumption).
The channel noise values are measured directly by the RVP8 during noise sampling. Whether to
use these measured values to correct for the noise power when computing a channel power is
optionally configured in the TTY setups. The choice is made in the mp TTY setup question
“Polarization Parameters NoiseCorrected:YES/NO”. If enabled, every time that a channel
power is calculated, the noise power is subtracted.
This has some interesting effects. With no noise correction, ZDR values in weak signal regions
will be biased by noise toward 0 dB (equal power), while if noise correction is enabled the
values will be unbiased but will show substantial deviation over the region. The choice is up to
the user.
Clutter Filtering
Clutter filtering is available for all four cases. The use of clutter filters should be carefully
considered since many polarization parameters such as ZDR and LDR require highly accurate
bin–to–bin consistency. The clutter filters will attenuate some small amount of weather near
zero velocity and the amount could be slightly different at the two polarizations. When using the
clutter filters, users should verify that the functioning is acceptable for their application.
The standard moments (T, Z, V, W) are filtered in the usual manner by selecting a clutter filter
(other than Filter #0 which is the All Pass filter). To enable clutter filtering of the polarization
variables, the mp TTY setup question “Polarization Parameters Filtered” should be set to YES.
The polarization algorithms will then be calculated with filtered time series. Note that filtering
can be effectively disabled for the polarization variables by selecting Filter #0 even if the mp
setup is set to enable filtering. This allows users to make easy comparison of the filtered vs
unfiltered results using their application software without having to change the RVP8 setup.
The s’ notation for filtered samples shall be dropped in the algorithm discussions. It is
understood that the input samples in all cases may be either filtered or unfiltered according to the
user’s choice in the TTY setups.