1. Doppler Dilemma Ideal in forecasting: Would you settle for:
ability to detect 100 kt winds out to 200 km that would be nice.
Would you settle for:
100 kt winds out to 120 km?
What about detecting winds out to 240 km?
With some very clever techniques both of the above can be done.

2. Example of Winds above the Nyquist
Above the Nyquist velocity the phase shift implies winds of opposite direction.

3. Solving the Doppler Dilemma
Use 2 different PRF’s to increase the unambiguous velocities

4. Using 2 PRF’s to “See” Winds above the Nyquist - Example
Real radial component 15 m/s away
900 PRF will “fold” and show 9 m/s towards ; the 1200 PRF will show 15 away
If velocity is 20 m/s away both will fold 1200 will show 4 towards towards.

5. Unfolded Winds
Unfolded Winds
For distinct real wind ranges the difference in the reported “folded” winds for the 2 PRF’s will be constant
this can be used to calculate what “fold” you are in and compute the real winds.
Allows us to unfold and be able to detect winds to 48 m/s

6. Unfolding Errors
Can occur when you are near the boundaries of the fixed differences between the PRF’s
Produces “speckles” 24 or 32 m/s different from adjacent returns.

7. Factors in spectral width
the wind shear in the sample volume
the motion of the antenna
particle motions within the sample volume due to variations in particle size (ie, the droplet size distribution)
vertical velocity

8. Summary
Using 2 PRF’s allows us to overcome the Doppler dilemma.