[Datastream #ZFY-296505]: radar dBZ -> mm ?

Hi Martin,

Sorry I was not able to respond to your inquiry before now...

re:
> thanks for telephone conversation just now,

I thought our conversation was very informative!

re:
> I'm working on a radar project and need a way to convert dBZ values to
> mm, I got some hits in the mailinglist archive that Steven "Chiz"well
> worked on this a year or two ago,
> 
> would it be possible to get some more information on how he solved this?
> (he did mm -> dBZ but that can be fixed)

Here is the information that Chiz sent me regarding the conversion from
precipitation rate back to reflectivity for Canadian radar products
we get from Pelmorex:

"In the routine radar_grid.c I have:

        switch ( ptype ) {
            case 1: /* Rain */
                dbz = 10 * log10( 295 * data[2] * 1.43 );
                data[2] = dbz;
                break;
            case 0: /* Snow */
                dbz = 10 * log10( 1780 * pow(data[2],2.21) );
                data[2] = dbz;
                break;


The ptype is given in the line of the file, so that wasn't a problem."

Ptype refers to the type of the product we are getting from Pelmorex.
As you can see, the Z-R relationship that Chiz used to convert from
precipitation rate back to reflectivity was dependent on a gross
characterization of the type of precipitation represented in the
product.

I just did a Google (tm) search using 'reflectivity to precipitation rate'
as a search key to get an idea of the breadth of information that is available
for Z-R relationships.  As expected, there are _lots_ of articles on this 
subject!
The two that I would definitely read are:

REFLECTIVITY-RAINFALL RATE RELATIONSHIPS IN OPERATIONAL METEOROLOGY
http://www.srh.noaa.gov/tae/?n=research-zrpaper

How does the radar calculate rainfall rates?‎
http://www.desktopdoppler.com/help/nws-nexrad.htm#rainfall%20rates

I would also read through the links under:

Scholarly articles for reflectivity to precipitation rate
http://scholar.google.com/scholar?q=reflectivity+to+precipitation+rate&hl=en&as_sdt=0&as_vis=1&oi=scholart

re:
> Many thanks in advance

No worries.  Again, I apologize for the delay in getting this back to you.

> ps we have also the 'merging' of neighbour countries radar data to solve

Yes.  We found that compositing the base reflectivities at the lowest radar
tilt for the WSR-88Ds in the U.S. results in a very useful product.  Just so you
know, the compositing is done using capabilities that Chiz added to GEMPAK a
few years ago, and one can easily take advantage of his work by using the
Unidata distribution of GEMPAK.


Cheers,

Tom
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Ticket Details
===================
Ticket ID: ZFY-296505
Department: Support Datastream
Priority: Normal
Status: Closed