[aprssig] future problems with NWS radar images? Part I of at least 2
Gerry Creager N5JXS
gerry.creager at tamu.edu
Tue Mar 29 09:55:49 CST 2005
I can talk a bit about RIDGE. That initiative comes out of the Southern
We're more'n a little familiar with Level II radar data here. I'm
generating a *LOT* of Level II gif images already.
As Pete points out later, the current projects are polar stereographic.
This works OK for small range plots, and is the best representation
for them to use, overall. The distortion, as I indicated, isn't too bad
for radar-service-area size plots vice unprojected (Lat/Lon) images.
When I prepare the CONUS radar images (and there are things happening
there for the UI-view world, and eventually the Xastir world to get
OGC-compliant WMS imagery; if other authors are interested, contact me
off-list) they're done as a cylindrical equidistant projection:
Unprojected, Lat/Lon. This is done to make life easier for the various
NWS started making data widely available to the community in a "new" and
less processed format about a year ago: Level II. First, a bit of
Level III images are created at each individual radar site, as jpegs,
then munged and transmitted in a completely different format that allows
recovery of the inherent data. At least 15 separate products are
created, in base reflectivity at various antenna elevations, storm and
radial velocities, hail parameters, vertical wind profiles, and
vertically integrated liquid. Resolutions are 1km x 1km per pixel for
all polar-plot products. I use Unidata's Gempak programs to create the
various images from Level III (and Level II) data.
Since I don't trust the list to not truncate, here's the end of part I.
Wes Johnston wrote:
> I started a conversation with my local NWS data guru about getting transparent
> doppler images (with the gridding and county line overlays), and he has
> referred me to a man up in Maryland. In my conversation with the guy in MD, he
> let the cat out of the bag that they are redoing the nexrad radar websites and
> are adding some glitzy graphics, but will also offer transparent images. The
> red flag went up when I looked at the _projection_ they use. It is no longer
> orthogonal! It's a spherical projection that looks like it'll make the doppler
> radar GIF files pulled from the NWS sites unsuitable for findu, ui-view,
> winaprs, and xastir....
> Here is the page they sent me as a sample:
> Here is the raw GIF file:
> Does anyone else have any information as to where the NWS is going here? Are
> they going to really use this spherical projection?
> aprssig mailing list
> aprssig at lists.tapr.org
Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University
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