Why does NEXRAD Level 2 Archive have no velocity data in slice(0)

[Paddy McCarthy]

Hi-

Any chance one of you knows why the lowest slice for the velocity field is slice(1) in the NEXRAD Level 2 Archive files, while reflectivity has a slice(0) ? I've been searching for several hours this weekend and can't find a reason for this in the Level 2 data description.

To be accurate I should say that when I *plot* slice(0) velocity, it always shows up empty. 
There is data there, but it does not show up on the plots. All the values are masked.

Thanks in advance for any help, 

-Paddy McCarthy

National Center for Atmospheric Research

[sherma...@gmail.com]

Hi Paddy,

Hmm, I'm honestly not sure, is this data from SAIL? I would maybe check with Ryan May from Unidata, he might have an idea on the scan strategy, I'm honestly not sure. Talked to Scott as well and thinking Ryan might know

Zach S.

[Paddy McCarthy]

Thank you, Zach-

I did reach out to Ryan and he explained that the lowest two sweeps are "split cuts" of the lowest tilt angle. This makes sense, and if you look at the elevation data for the sweeps, they are indeed close to (but not exactly) 0.5 degrees.

From Ryan:

NEXRAD, in most volume coverage patterns, operates with the lowest few sweeps/elevations collected using so-called "split cuts". In a split cut, the radar collects one full rotation at an elevation with a low PRF (high unambiguous range) to collect the power-based measurements (reflectivity + dual pol), then does another full rotation at the same elevation with a higher PRF (lower unambiguous range and higher unambiguous velocity) to collect the Doppler-based measurements (velocity and spectrum width). The power data from the first part of the split cut is used to identify (and possibly fix) any range ambiguity/folding in the Doppler data from the second part. Both sweeps from the split cut are written to the final data, but separately.

This is used to allow better data quality and clutter filtering than the batch mode or even single PRFs used at higher elevations. The downside is that this becomes a bigger chore to deal with on the data processing end since you have two complete sweeps at e.g. 0.5 elevation.

[sherma...@gmail.com]

Ah gotcha makes sense. Yeah that helps clear that up. Thanks for posting his response Paddy!

Cheers,

Zach S.