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[THREDDS #HEL-720643]: NEXRAD 'Radial Velocity'

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  • Subject: [THREDDS #HEL-720643]: NEXRAD 'Radial Velocity'
  • Date: Fri, 22 Feb 2013 09:27:21 -0700
Bruce,

Looking at the variable attribute, you will see the _Unsigned = "true" 
attribute.  You'll want to convert the unsigned byte to a short.  Note that 
when converting, you cannot take absolute value, as this mapping shows:
 
 byte short
 ...
 125 = 125
 126 = 126
 127 = 127
 -128 = 128
 -127 = 129
 -126 = 130
 -125 = 131
 -124 = 132
 ...
 
 Here's the java code to make the conversion:
 
 static public short unsignedByteToShort(byte b) {
 return (short) (b & 0xff);
 }

The scale factor and offset are exactly what you would expect - scale by 0.5 
and subract 64.5, respectively.

Hope this helps!

-Lansing Madry
  Unidata
  Boulder, Colorado

> Tech/Help,
> 
> I am trying to work with NEXRAD II data files to extract radial velocity.
> I have been able to convert the files I have to a NETCDF format (using
> your 'java' utility) to more easily access the data I need.
> 
> Within the NEXRAD files the 'RadialVelocity' field is labeled as in
> units of 'm/s', but the actual data are in a 'byte' format (ranging in
> value from -127 to +127).  Could you direct me to where I find out how
> to convert the 'byte' data into a floating point velocity in 'm/s' (the
> header also lists an 'scale_factor' of 0.5, and an 'offset' of -64.5)?
> 
> Peace,
> 
> BJ
> 
> --
> o       o     \ !      \|      \ /      |/      ! /    o /     o
> -|-    -/-      --o      \-      |      -/      o--     -\     -|-
> /_\_____|\_____/__\____ /_o_____/o\_____o_\_____/__\____/_\____/_\
> Bruce Jackson
> Air Resources Board/Technical Support Division
> Sacramento, California 95812
> address@hidden<mailto:address@hidden>
> (916)324-6916
> 
> 
> 


Ticket Details
===================
Ticket ID: HEL-720643
Department: Support THREDDS
Priority: Normal
Status: Open