Vaisala RVP900, User Manual, Page: 47 / 484

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Speckle Filter Processing (page 210)
3.3.8 Velocity Unfolding
The RVP900 processor can unfold mean velocity measurements based on a dual PRF
algorithm.
In this technique, 2 radar PRFs are used for alternate
N -pulse processing intervals. The
internal trigger generator automatically produces the correct dual-PRF trigger. An external
trigger can also be applied.
For external triggers, the
ENDRAY_ output line indicates when to switch rates. RVP900
measures the PRF to determine which rate (high or low) was present on a given processing
interval. It then unfolds based on a 2:3, 3:4, or 4:5 frequency ratio.
Table 8 Example Unambiguous Velocity Intervals
PRF1 PRF2 Unambiguo
us Range
(km) Unambiguous Velocity (m/s) Unfolding
3 cm
Wavelength 5 cm
Wavelength 10 cm
Wavelength
500 * 300 3.75 6.25 12.50 None
1000 * 150 7.50 12.50 25.00
2000 * 75 15.00 25.00 50.00
500 333 300 7.50 12.50 25.00 Two times
unfolding
1000 667 150 15.00 25.00 50.00
2000 1333 75 30.00 50.00 100.00
500 375 300 11.25 18.75 37.50 Three times
unfolding
1000 750 150 22.50 37.50 75.00
2000 1500 75 45.00 75.00 150.00
500 400 300 15.00 25.00 50.00 Four times
unfolding
1000 800 150 30.00 15.00 100.00
2000 1600 75 60.00 100.00 200.00
3.3.9 Autocorrelations
The autocorrelations R0, R1, and R2 are produced by Pulse Pair, Random Phase, and
DFT/FFT modes. The way that they are produced is different for each mode, particularly
with regard to the filtering.
Chapter 3 – Functional Description
45