DLOC Principles of Meteorological Doppler Radar:
WSR-88D Fundamentals

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Previous Page: Maximum Unambiguous Velocity (Vmax) and PRF

Doppler Dilemma

Both the Rmax and Vmax are dependent on the PRF. However, they do not have the same dependence. Notice in Equation (7) and Equation (9) that Rmax has an inverse dependence on the PRF, while Vmax has a direct dependence.

Equation 7.  Rmax.  Click for Long Description.
Equation 9.  Maximum unambiguous velocity (Vmax).  Click for long description.

An increase in the PRF will result in a decrease in Rmax but an increase in Vmax. Also, a decrease in the PRF will result in an increase in the Rmax but a decrease in the Vmax. Although a high Vmax is desirable for obtaining quality Doppler velocity information, this comes at the expense of using a high PRF and thus a shorter unambiguous range (Rmax). The high PRF results in a short Rmax and increases the chance for multiple trip echoes. See Section 6-7 for the various operational PRFs and the corresponding Rmax and Vmax values. The dependencies that Rmax and Vmax have on PRF is important to WSR-88D operators because PRFs are (in some cases) editable.

A low PRF is desirable for target range and power, while a high PRF is desirable for target velocity. The inability to satisfy both needs with a single PRF is known as the Doppler Dilemma. The Doppler Dilemma is addressed by the WSR-88D with algorithms that will be presented as part of Topic 3.

Next Page: Practice Exercise #3
or continue on to:
Section 4: Range Issues