S-PolKa Known Problems

S-PolKa REFRACTT06, Marshall Field Site, Colorado
May 2006 - Aug 2006

Known problems are broken down into two categories: S-band/general problems, and Ka-related problems.

Support information for some of these problems is found in the Operators' Log, and in the general report for S-Pol on this project (see the table of contents)

S-band and General


Ground Clutter and Ground Clutter Filter

The Marshall field site is located in elevated terrain compared to its surroundings. This situation is less than ideal for S-band side lobe ground clutter contamination. Accordingly the ground clutter filters were applied throughout the project. The filter is a 4-pol elliptic filter with a notch width from approximately -0.5 to 0.5 m/s. The strong ground clutter that leaks through this filter can be caused by several effects: First, the clutter is stronger than the windowing response function causing the clutter power to be spread throughout the Nyquist interval. Second, the spectrum width of the clutter is too wide for the notch width of the clutter filter. Both of these situations will result in ground clutter leaking through the clutter filter. Thus ground clutter leakage should not be interpreted as a malfunctioning filter. The Ka-band ground clutter is roughly 30 to 40 dB lower than S-band, so no filter was required.

Improper PPI scanning, 02-Aug-2006

For the period 15:45 thru 17:46 on 02-Aug-2006, the radar scan controller did not function properly. Scans were incomplete, or in alternating NE or SW 180° sectors, with precession of those sectors.

Restarting the scan control computer corrected this problem.

Dropped beams

Both RDA1 and RDA2 experienced randomly dropped beams. It manifested itself in wedges of missing data between 5 and 15 degrees wide in azimuth. Although the cause was not investigated in the field, a script to patch the problem in post-processing was created for the final data set. This simply replaced the missing data in RDA1 with the data from RDA2. This leaves open the possibility that both RDA's had missing data resulting in unrecoverable data gaps. This is very rare.

Extra PPI scan per volume

The scan control software had an issue completing the volumes consisting of 180 deg PPI scans which caused the highest elevation angle to be repeated (Usually 10.2 deg during REFRACTT 2006). Thus there are two 10.2 deg scans for each of these volumes. This problem was not experienced with the 360 deg scan volumes.

Mis-matched S and Ka beam sampling

For different (and sometimes extended) time periods on July 14, 16, 17, 19, 30 and Aug 9, the Ka sampling was non-optimum. Either the samples-per-beam or the PRF was different from the optimal value, resulting in more Ka beams than S-band beams and a beam mis-match between the two systems.

See the various beam info files or the Ka statistics files for details.

--- Bob Rilling --- / NCAR Earth Observing Laboratory
Created: Fri Sep 22 10:54:04 MDT 2006
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