Bart_Comstock
EF5
Why is there a intermittent void in velocity data from scan to scan that always seems to coincide with VCP 12?
I could give many examples of this with INX and SRX.
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VCP Training
- Thread starter rdale
- Start date
I could give many examples of this with INX and SRX.
Randy Bowers
EF1
If you can give specific dates and times, I'd like to take a look. You said 3/12/06 is a good example of this happening? I'll pull the archive data from NCDC. Perhaps it's a dealiasing error? Is it range folding (or "purple haze" as it's been coined by others)? Were you using Level II or Level III data, and if both did you compare the two? Admittedly, VCP 12 does tend to have some pretty severe issues with range folding from time to time. VCP 212 has helped to address this issue though.
rdale
EF5
Did you go through the training yet? There's a very handy cheatsheet which explains when each mode works best. VCP11 is rarely on that list.
Bart_Comstock
EF5
It isn't purple haze. It is dealiasing error. This is a common problem too. Take a look around 0305z - 0349z when the supercell is moving from Cherokee County, OK through Benton County, AR.
Randy Bowers
EF1
I downloaded both Level II and Level III data for KSRX. The reason I asked if you had viewed the Level II and/or Level III data is that sometimes Gibson Ridge's GRlevel2/2ae dealiasing method seems to work better than the NWS method. Other times the NWS method works better than Gibson Ridge's. Level II data is raw and not dealiased (until it's done by the viewing software, i.e., GRlevel2/2ae), whereas Level III data is dealiased at the RPG, and transmitted to the world already dealiased. There are some serious issued as the storm crosses into Arkansas (03:45z volume scan) when viewing the Level II data in GRlevel2/2ae. Here is a comparison of the Storm Relative Velocity of the lower four tilts of both Level II and Level III:
Level II data viewed in GRlevel2 Analyst
Level III data viewed in GRlevel3
Notice the dealiasing errors on the lowest three tilts when viewing the Level II data in GRlevel2 Analyst with Gibson Ridge's dealiasing enabled. Notice that these errors do not exist at the 1.8 degree elevation angle nor on either of the four lowest tilts displayed in GRlevel3.
Even though the RPG's dealiasing worked well in this particular case, there certainly are times when it does not. I've seen some pretty substantial errors in the past. Examining the next tilt up from the lowest will sometimes reveal a much cleaner image. With the increased vertical resolution of VCP 12, the 0.9 degree elevation angle (one above the lowest) isn't that bad of a compromise considering the second lowest tilt in VCP 11 is 1.45 degrees, which is even higher than the third lowest tilt of VCP 12.
These errors are not unique to VCP 12 and are inherent to the limitations of the radar itself. No matter what VCP is being used, it's important to know your environment well. Being able to recognize a potentially tornadic storm using techniques other than 0.5 degree SRV is important.
Other members would undoubtedly be able to explain the dealiasing methods in more detail. But, hopefully the information I provided helps at least some.
