Incorrectly dealiased velocity data can seriously impact certain WSR-88D algorithms and products. Mean Radial Velocity products will be difficult to analyze when contaminated with incorrectly dealiased data. To determine the extent of the dealiasing problem, it is recommended that earlier displays of these products be examined to determine if there is time or space continuity. In addition, other elevation angles of the Mean Radial Velocity products may be used to determine if there is vertical continuity.

Algorithms and products that ingest mean radial velocity data can output incorrect results when such data are used. In the case of the mesocyclone detection algorithm, there will likely be a lack of vertical continuity of incorrectly dealiased data. Consequently, only uncorrelated shears should result from using aliased data. In the rare event of a tornadic vortex signature being output in the vicinity of an identified mesocyclone because of vertical continuity of incorrectly dealiased data, other products should be examined to verify the existence of a severe thunderstorm.

It is expected that incorrectly dealiased data will not have a large impact on Combined Shear products because of the amount of averaging of data done by the algorithm.

Second trip echoes (range folding) occurs when the radar hears a previous pulse, while listening for the most recent pulse.

Due to the sensitivity and narrow beam width of the WSR-88D, precipitation echoes beyond 250 nmi will occasional y appear in closer range due to range folding. However, far more significant are the range ambiguities in the doppler velocity and width fields caused by the WSR-88DS pulsed doppler sampling interval (referenced in part B of the FMH-11). For any pulsed doppler system, the product of the unambiguous range and the doppler Nyquist interval is a constant function of the wavelength of the radar and the speed of light. Decreasing the PRF allows for a longer listening time, thus increasing the unambiguous range, but, this lower PRF creates a problem in determining radial velocities.

High PRFs are required for high velocity measurements and low PRFs are required for long ranges. The solution to this dilemma lies in finding a balance between the effects of velocity aliasing and range folding. This dilemma is caused by physical restrictions based on the laws of nature. To solve this dilemma, the WSR-88D will use several methods to work around these restrictions. One method is to operate at variable PRFs; the second is to collect refractivity information at low PRFs and velocity information at high PRFs. The two sets of information collected are compared, then processed to estimate true radial velocities and ranges.

The radar interprets velocity and spectrum width returns from beyond the ambiguous range as occurring within the range. Range dealiasing software has been implemented in the Radar Data Acquisition (RDA) component preprocessor. The purpose is to attempt to replace range-folded doppler data to its proper range. This software compares radar power returns from the possible ranges of doppler velocity and spectrum width data, If the power at one possible range is more than the power at the other ranges, the data are assigned to that range and the doppler data from the other ranges are considered ambiguous. If the power from the different cringes is within 10 dB, the doppler data at all those ranges are considered unambiguous. Ambiguous doppler data are flagged as range folded, treated as missing by all algorithms, and are displayed as purple (adaptable) at the principal user processor (PUP).

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