gribscan

The gribscan utility is used for extracting grid info from GRIB data files. Its features include grid/product information, gridded output in ASCII, binary, and/or grib format, plus automatic "scanning" for GRIB records so that you don't have to know the physical layout of the data to scan it.

The command sytax is:

gribscan [-i ifname] [-o ofname] [-file options] [-processing options] [-display options]

Where:

ifname
This is the input grib file name. If -i ifname is omitted, gribscan will prompt the user for a file name.

ofname

This is the output file name WITHOUT an extension. If -o ofname is omitted, a default file name of zy0x1w2.type is created where type is:
asc - ascii
grb - GRIB
dat - a stream of floats (GrADS format)

File Options:

-og
gribscan will return output in GRIB format

-oa

gribscan will return output in ASCII format (%8g in C-language syntax)

-of

gribscan will return output as a stream of floats. This is machine dependent and is 64-bit on Crays and 32-bit elsewhere.

Processing Options:

-sNNN
Specifies the max number NNN of bytes between GRIB messages in the file. The default is 500 and it is assumed that you want to ignore junk (e.g., comm stuff) between data.

-spNNN

Selects parameter # NNN (e.g.,-sp11 for temperature)

-slNNN

Selects level # NNN (e.g., -sp500 to get 500 mb fields)

-stNNN

Selects tau # NNN (e.g., -st12 to get t=12 forecasts)

-hNNN

Specifies a fixed file header of NNN bytes. If omitted, the default is to seek the first GRIB message automatically, but if you know NNN, it is more efficient to specify it.

Special note to NMC users: The once "standard" 81-byte header in an NMC GRIB file contained the string "GRIB". Unfortunately, the same string is part of the GRIB indicator section itself! Thus, an automatic scan for GRIB to demark the start of the data will fail if the 81-byte header is present! When in doubt (or failure) try using the -h81 option.

Note: These processing options can be used simultaneously to output a very narrow set of fields.

Display options:

-q     Quick output to extract stuff GrADS gribmap cares about
-q1    One-line quick output
-d     Comma delimited mode
-v     Verbose mode for diagnostics
-bd    Binary data section info
-gv    Uses the NMC GRIB variable table to output mnemonic, title, and units
-gd    Output info from the grid defn sec
-S     Silent mode; NO standard output

Examples

1. A "quick" scan to get the info GrADS cares about:
   gribscan -q -i eta.T12Z.PGrbF48 | grep 184

   Gives the result:

   184,F,135,108,100,0,100,0,1e+09,T,1994,8,29,12,0,1,48,0,G,104,BDTG,94082912

   Where:

   184      field # in the file
   F        field data
   135      param #
   108      level indicator
   100      level
   0        l1 byte 1 of level
   100      l2 byte 2 of level
   0        time range indicator
   1e+09    decimal scale factor
   T        time data follows
   1994     year
   8        month
   29       day
   12       hour
   0        min
   1        forecast time unit (hour)
   48       t=48 h forecast
   G        grid param follows
   104      NMC grid #104
   BDTG     Base date-time-group (yymmddhh) follows

   Comma delimited output:

   gribscan -d -i eta.T12Z.PGrbF48 | grep 184

   Gives the same results as the previous example but arranged differently:

   PDS,184,104,135,108,100,0,100,1994,8,29,12,0,1,48,0,0,1e+09

   A full listing:

   gribscan -d -gv -bd -gd -i eta.T12Z.PGrbF48 | grep 184

   Gives the following results:

   PDS,184,104,135,108,100,0,100,1994,8,29,12,0,1,48,0,0,1e+09,mconv,Horizontal moisture divergence,[kg/kg/s],GDS,5,147,110,-139.475,90.755,0.354,-0.268,-105.000,33536.000,0,1,0,BDS,12,-646.844,16170,4825059,26366

   Where:

   104          grid id
   param #135   mconv,Horizontal moisture divergence,[kg/kg/s]
   BDS          binary data section
   646.844      ref value 16170 - # of points
   4825059      starting byte of the data
   26366        length of the grib message
   

   Note that eliminating the -d option would result in a fixed-column type output.

   Output a selected few fields in GRIB:

   gribscan -og -sp135 -q -i eta.T12Z.PGrbF48 -o eta.135

   Writes out all GRIB message containing the 135 parameter to the file eta.135.grb. A subsequent execution of gribscan on eta.135.grb would return:

   1, F ,135,108,100,0,100,0,1e+09, T,1994,8,29,12,0,1,48,0, G ,104, BDTG, 94082912 2, F,135,108,21860,85,100,0,1e+09, T ,1994,8,29,12,0,1,48,0, G ,104, BDTG, 94082912