User's Guide

GETNCEP

Return a complete NCEP water vapor image

Function:

Create a water vapor image by retrieving an NCEP image. Also create a QC image that indicates the origin of the water vapor values.

Parameters:

HOUR
Acquisition hour used to determine which NCEP model to retrieve:


HOUR          Z model
-------       --------
0-2             00
3-8             06
9-14            12
15-20           18
21-23           00 (next day's)

MONTH
Month of output image

DAY
Day of output image

YEAR
Four digit year of output image

OUT
Filled water vapor output image. A 1-band image of water vapor values.

QC
Quality Control output image. A 1-band image containing QC values which indicate the origin of water vapor values. (See User Note 3)

SILOBASEDIR
Base SILO directory (See User Notes 1 and 2)

WATERBASEDIR
Base water vapor directory (See User Note 1)

BACKDIR(--)
Backup water vapor directory (See User Note 5)

Examples:

  1. LAS> getncep hour=7 month=6 day=4 year=1998 out="jun04water" qc="jun04qc" silobasedir="/avhrr" waterbasedir="/sgs4/km1/adaps/images"

    The NCEP daily observation for June 4, 1998 is retrieved from /avhrr/ncep_watervapor/1998. The output images created will be called jun04water and jun04qc.

Description/Algorithm:

The input parameters are combined to create image names of the daily observation. The SILO is checked to see if the closest daily NCEP image exists. If it does, this NCEP image is returned. If not, the SILO is checked to see if an NCEP image for 6 hours later exists. If it does, this NCEP image is returned. If not, the SILO is checked to see if an NCEP image for 6 hours earlier exists. If it does, this NCEP image is returned. A QC image is created and returned along with the NCEP water vapor image.

Nonfatal Error Messages:

  1. [getncep-nocep] Unable to retrieve NCEP image

    The daily NCEP image was not on the SILO or the SILO was not operational. Verify that the SILO is operational.

  2. [getncep-noqc] Unable to retrieve a QC image

    The appropriate QC image was not available. Contact the system administator if this error persists.

Fatal Error Messages:

  1. [getncep-fatal] Fatal error encountered

    A fatal error was encountered during processing. Processing is terminated. The error message that is displayed immediately preceding this message is the specific error that was encountered.

User Notes:

  1. All water vapor images are stored in directory structures with a base directory under which directories for daily climatologies and daily observations by year are contained. The daily observation directories (e.g. 1999) are only stored on the SILO. No daily climatologies exist for the NCEP dataset, only daily observations.

    
       basedir \--- tovs_watervapor \--- dailyfillam
       	                        \--- dailyfillpm
                                    \--- 1979
    	                        \--- 1980
    	                        \--- ...
    	                        \--- 2000
    
       basedir \--- ncep_watervapor \--- 1979
    	                        \--- 1980
    	                        \--- ...
    	                        \--- 2000
    
    

  2. The QC band contains values that indicate the origin of the water vapor value for the pixel in the corresponding output image. The values are:

        0 - pixel value from daily TOVS observation
        1 - pixel value from daily TOVS climatology
        2 - pixel value from monthly TOVS climatology
        3 - pixel value was interpolated in monthly TOVS climatology
        5 - pixel value from NCEP model (closest hour)
        6 - pixel value from NCEP model ( + 6 hours)
        7 - pixel value from NCEP model ( - 6 hours)
    

  3. Temporary files are created (and eventually deleted) in the same directory as specified in the OUT parameter.
  4. The backup directory parameter has been added to allow users to work around silo problems. If water vapor images are not available on the silo or the silo is down, users can place image files in the backup directory and specify this directory in the parameter BACKDIR. When invoked the silo will be checked first and, if the file cannot be retrieved, the backup directory will be used.

    The backup directory is only a backup for the silo and as such only the img files are copied. There are cd's in the archive containing all TOVS and NCEP images except the current year. Current years images are archived in January of the following year. The CD's are stored as code 049; project AVHRR greeness; and description: TOVS/NCEP water vapor YYYY. The ADAPS software person should have an online backup of current year images available.