Vaisala RVP900

Chapter 2 _______________________________________________ Introduction and Specifications
VAISALA_______________________________________________________________________ 45
or DFT may be performed to return to time domain after clutter
removal. Autocorrelations are then computed in the time domain.
- DFT/FFT Mode—Filtering for clutter is performed in the frequency
domain using both fixed width filters and the Gaussian Model
Adaptive Processing (GMAP) technique. Autocorrelations are
computed from the inverse transform.
- Random Phase—Filtering for clutter and second trip echo is
performed in the frequency domain by adaptive algorithms.
Autocorrelations are computed from the inverse transform.
2.9.1.2 Time (Azimuth) Averaging
The autocorrelations are based on input "I" and "Q" values over a
selectable number of pulses between 8 and 256. Any integer number of
pulses in this interval may be used, including DFT/FFT and random phase
modes.
Selectable angle synchronization using the input AZ and EL tag lines
assures that all possible pulses are used during averaging for each, for
example, 1 degree interval. This minimizes the number of "wasted" pulses
for maximum sensitivity. Azimuth angle synchronization also assures the
accurate vertical alignment of radial data from different elevation angles in
a volume scan (see below).
2.9.1.3 TAG Angle Samples of Azimuth and Elevation
During data acquisition and processing, it is usually necessary to associate
each output ray with an antenna position. To make this task simpler, the
RVP900 samples 32 digital input "TAG" lines, once at the beginning and
once at the end of each data acquisition period. These samples are output
in a four-word header of each processed ray. When connected to antenna
azimuth and elevation, the TAG samples provide starting and ending
angles for the ray, from which the midpoint can be deduced. Since the bits
are merely passed on to the user, any angle coding scheme may be used.
The processor also supports an angle synchronization mode, in which data
rays are automatically aligned with a user-defined table of positions. For
that application, angles may be input either in binary or BCD.
2.9.1.4 Range Averaging and Clutter
Microsuppression
To improve the accuracy of the reflectivity measurements, the RVP900
can perform range averaging. When this is done, autocorrelations from
consecutive range bins are averaged, and the result is treated as a single