User's Guide

GETWATER

Return a complete water vapor image

Function:

Create a water vapor image by retrieving an NCEP image or by combining data from a daily TOVS observation and TOVS climatological data. 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

SATID
Satellite ID. The one- or two-digit satellite ID, for example: if satellite is NOAA-14 use 14 for SATID. NOTE: This parameter is only relevant for TOVS data.

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("/DMF/EDC/AVHRR")
Base SILO directory (See User Notes 1 and 2)

WATERBASEDIR("/SGS4/KM1/ADAPS/IMAGES")
Base water vapor directory (See User Note 1)

TIMEFLAG("PM")
Time of day flag. Indicates whether the water vapor should come from the morning or afternoon observation. NOTE: This parameter is only relevant for TOVS data.

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

Examples:

  1. LAS> getwater hour=7 month=6 day=4 year=1998 satid=14 out="jun04water" qc="jun04qc" silobasedir="/avhrr" waterbasedir="/sgs4/km1/adaps/images" timeflag="pm"

    The closest of three daily NCEP models for June 4, 1998 is retrieved from /avhrr/ncep_watervapor/1998. If unsuccessful, a TOVS image is constructed from a daily observation for the afternoon of June 4, 1998 and/or TOVS daily climatologies for June 4th pm. The daily climatologies will be found in directory /sgs4/km1/adaps/images/tovs/dailyfillpm and the daily observation on the silo in directory /avhrr/tovs_watervapor/1998. The output images created (whether NCEP or TOVS data) will be called jun04water and jun04qc.

Description/Algorithm:

The input parameters are combined to create image names of the daily observation and climatology images. The SILO is checked to see if an acceptable NCEP image exists. If so, the NCEP image is returned along with an appropriate QC image. An acceptable NCEP image is defined as an NCEP image which lies (1) closest to the acquisition time, (2) subsequent to the closest NCEP image, or (3) previous to the closest NCEP image (NCEP images are available at 6 hour intervals). If an NCEP image isn't available, the SILO is checked to see if a daily TOVS observation exists. If a daily TOVS observation doesn't exist or there is an error copying it from the SILO, an image consisting of TOVS climatology is generated. The image is filled first with daily, then with monthly climatology data and a QC image is created.

Nonfatal Error Messages:

    None.

Fatal Error Messages:

  1. [getwater-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.

  2. [getwater-nowv] No water vapor image returned

    No NCEP or TOVS water vapor image was returned. Ensure that the SILO is operational and retry.

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 daily 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.