Chapter 6 ______________________________________________________ Processing Algorithms
VAISALA______________________________________________________________________ 197
the first pulse encountered, and an additional pipeline delay is introduced
to allow the estimator to completely settle. Thus, valid corrected data are
produced even when the RVP900 is alternating rapidly between different
data acquisition tasks, for example, in a multi-function ASCOPE display.
The additional pipeline delay will not affect the high-speed performance
when the RVP900 runs continuously in any single mode.
For amplitude correction to be applied, the instantaneous Burst/COHO
signal level must exceed the minimum valid burst power specified in the
Mb setup section. If that level is not met, for example, if the transmitter is
turned off, then no correction is performed. Thus, the amplitude correction
feature conveniently "gets out of the way" when receiver-only tests are
being performed.
The maximum correction that will ever be applied is ±5 dB. If the burst
power in a given pulse is more than 5 dB above the mean, or less than 5 dB
below it, then the correction is clamped at those limits. The power variation
of a typical transmitter will easily be contained within this interval (it is
typically less than 0.3 dB).
Instantaneous amplitude correction is a unique feature of the RVP900
digital receiver. Bench tests with a signal generator reveal that an
amplitude modulated waveform having 2.0dB of pulse-to-pulse variation
is reduced to less than 0.02 dB RMS of (I,Q) variation after applying the
amplitude correction.
6.2 Time Series (I and Q) Signal Processing
6.2.1 Time Series Processing Overview
This section describes the processing of the radar time series data (also
called linear "video" or "I" and "Q") to obtain the meteorologically
significant "moment" parameters: reflectivity, total power, velocity, width,
signal quality index, clutter power correction, and optional polarization
variables.
Recall that the time series synthesized by the FIR filter consist of an array
of complex numbers:
where "j" is - 1
1/2
. The time series, are the starting point for all calculations
performed within the RVP900. There are several excellent references on
the details of I and Q processing.2 The top part of Figure 38 on page 197
shows I and Q values for a simulated time series using the ascope utility.
To Next Page
Loading...
Need help?
General