Known Problems

S-Pol IHOP_2002, Oklahoma Panhandle
May/Jun 2002

There were several known problems with S-Pol data or data quality during IHOP. This page presents a short summary of those problems, with links to further details.

Further insight into these and other problems may be gained through review of the Operators' Log for this project.

Zdr Bias

A bias in Zdr of -.08 dB was found through analysis of vertical pointing data. An adjust of +.08 dB has been added to all Zdr in the final data set.

Details of this work will be prepared.

Corrupted Data Recording

This is a significant problem that was noted in the field, but the cause could not be determined until the post-processing phase. Extensive post-processing from multiple data sources can eliminate most of the data problems, but there is still some net data loss (total loss is estimated at less than 1%).

Details are provided.

PIRAQ Processor Artifact (0.5° tilt)

The PIRAQ Radar Signal Processor had trouble making a transition between the usual 0.0° and 0.5° SUR scans. The processor would require a small amount of time to re-initiate the processor during the transition, due to changes in scan parameters (particularly, the number of samples per beam). The problem manifests itself as several (three to five) bad beams at the start of the 0.5° SUR scan. The collection of beams often has a banded, or "barber pole" structure; frequency of occurance is about one out of every three 0.5° SUR scans. The problem extends through the active range of the clutter filter (out to 120 km).

It is best to remove these bad beams from any analyses. An example is available.

Incomplete Surveillance Scans, 4/5 June

A scan control configuration error caused problems with the standard surveillance scanning on 4/5 June. SUR scans during this time are partial scans, only, before the antenna "notches up" to the next elevation. Time period affected is about 22:40 UTC 4-Jun thru 14:43 5-Jun. There is no post-processing method to correct for this scientist/operator error.

Incomplete RHI Scans, 15/16 June (and possibly other days)

The last RHI in a sequence of RHIs (a scan volume) was often prematurely terminated on 15/16 June. This likely was caused by an attempt to maintain precise schedule for conducting 0° SUR scans for refractive index. This behavior is mentioned to avoid confusing the data drop-out with the Corrupted Data Recording problem. The nature of the incomplete RHI scans was verified through review of the preserved real-time data stream.

Some additional details are provided.

Miscellaneous Data Artifacts

There are artifacts in the data that may be caused by natural or man-made phenomenon, or by very occasional problems with the radar itself. These should not be confused with systematic problems in the data set.

Some examples:

There are additional features in the data that are there by design. Particularly:

Bad scanning, 15/16 June

On 15/16 June, poor scan parameters were programmed into the scan controller. Many volumes were scanned at a rate of 64 samples per beam (not good for dual polarimetric parameters, and really pushing the tape drives and processor). As part of the problem, many 0.0° refractive index scans were not able to complete.

A more precise time bracket for this problem needs to be defined.

DBZ vs DZ; VR vs VE

Not truly a problem, but a quirk.

In the realtime IHOP sweep data files there were fields called DBZ and VR; in the post-processed data, these same fields are labelled DZ and VE. There's a difference in the PIRAQ-to-DORADE real-time vs post-processing translator code that seems to do this. A flag that can be set to name the fields the same way, but this has not routinely been used to produce a final project data set.

Tape Writing Failure, 14-Jun-2002, 18:27 to 22:33

The tape writing process on the second Radar Data Acquisition system failed. This, combined with the tape cache corruption, resulted in scans for this time being very choppy. Consideration should be given to using the realtime data stream for this time period.

--- Bob Rilling --- / NCAR Atmospheric Technology Division
Created: Mon Oct 28 16:17:22 MST 2002
Last modified: