User's Guide

AVHRRIN

Converts AVHRR archive images to LAS images

Function:

Converts an AVHRR archive image to a LAS image. Three subcommands are supplied to window the AVHRR image using line and sample, latitude and longitude, or a latitude range. The input image may be located on disk or on an AVHRR archive tape.

Parameters:

Subcommand -LINESAMP:
Line and sample window specification. The window is specified as a starting line, starting sample, number of lines, and number of samples.

IN
Input image. The name of the AVHRR archive image. IN must be the scene ID of the desired archive image on tape if COMMENT is supplied. Any windowing and subbanding options must be specified using SL, SS, NL, NS, and BANDS.

OUT
Output image. The name of the LAS image to be created.

SL(--)
Starting line. The first line of the AVHRR archive image to be converted. If defaulted, the image will be converted starting at line one.

SS(--)
Starting sample. The first sample of the AVHRR archive image to be converted. If defaulted, the image will be converted starting at sample one.

NL(--)
Number of lines. The number of lines to be processed. If defaulted, all of the remaining lines starting at SL will be processed.

NS(--)
Number of samples. The number of samples to be processed. If defaulted, all of the remaining samples starting at SS will be processed.

BANDS(--)
Band numbers. Specifies which of the bands from IN are to be converted to the LAS image. If defaulted, all of the bands will be converted.

COMMENT(--)
Description of tape. A text string sent to the operator's terminal describing the tape to be mounted. COMMENT should contain the tape library identification number and a short description of the tape. This will allow the operator to ensure the correct tape is mounted. If defaulted, the archive image is assumed to be located on disk.
Subcommand -LATLONG:
Latitude and longitude window specification. The window is specified as a starting and ending latitude and longitude.

IN
Input image. The name of the AVHRR archive image. IN must be the scene ID of the desired archive image on tape if COMMENT is supplied. Any windowing and subbanding options must be specified using SLAT, SLONG, ELAT, ELONG, and BANDS.

OUT
Output image. The name of the LAS image to be created.

SLAT
Starting latitude. The northernmost latitude that should be included in the LAS image. This value must be entered in degrees.

SLONG
Starting longitude. The westernmost longitude that should be included in the LAS image. This value must be entered in degrees.

ELAT
Ending latitude. The southernmost latitude that should be included in the LAS image. This value must be entered in degrees.

ELONG
Ending longitude. The easternmost longitude that should be included in the LAS image. This value must be entered in degrees.

BANDS(--)
Band numbers. Specifies which of the bands from IN are to be converted to the LAS image. If defaulted, all of the bands will be converted.

COMMENT(--)
Description of tape. A text string sent to the operator's terminal describing the tape to be mounted. COMMENT should contain the tape library identification number and a short description of the tape. This will allow the operator to ensure the correct tape is mounted. If defaulted, the archive image is assumed to be located on disk.
Subcommand -LATRANGE:
Latitude range window specification. The window is specified as a starting and ending latitude. The image can be windowed in the sample direction by specifying the nadir offset (number of samples to select each side of nadir.)

IN
Input image. The name of the AVHRR archive image. IN must be the scene ID of the desired archive image on tape if COMMENT is supplied. Any windowing and subbanding options must be specified using SLAT, ELAT, QUADNUM, AREAOPT, and BANDS.

OUT
Output image. The name of the LAS image to be created.

SLAT
Starting latitude. The northernmost latitude that should be included in the LAS image. This value must be entered in degrees.

ELAT
Ending latitude. The southernmost latitude that should be included in the LAS image. This value must be entered in degrees.

QUADNUM(5)
Quadrant number. The quadrant number is used to help specify the area of interest for AVHRR scenes that are at or near the pole. If defaulted, all scenes that do not cross either pole will be considered. See User Note 1.

   = 1: Quadrant 1
   = 2: Quadrant 2
   = 3: Quadrant 3
   = 4: Quadrant 4
   = 5: Any quadrant.  HRPT or LAC scenes
        that do not cross either pole.
   = 6: North pole.  The latitude range
        should cover the North pole.
   = 7: South pole.  The latitude range
        should cover the South pole.
   = 8: Both poles.  The latitude range
        includes both poles.

AREAOPT(FIRST)
Area option. Area of intersection to be selected. Some Global Area Coverage (GAC) passes can intersect an area of interest twice. In these cases AREAOPT can be used to indicate which intersection is to be selected.

  = FIRST:   First intersection
  = SECOND:  Second intersection

OFFSET(--)
Offset value. The number of samples to be selected from both sides of the center of the pass. If defaulted, the full width of the pass is selected.

BANDS(--)
Band numbers. Specifies which of the bands from IN are to be converted to the LAS image. If defaulted, all of the bands will be converted.

COMMENT(--)
Description of tape. A text string sent to the operator's terminal describing the tape to be mounted. COMMENT should contain the tape library identification number and a short description of the tape. This will allow the operator to ensure the correct tape is mounted. If defaulted, the archive image is assumed to be located on disk.

Examples:

  1. LAS> avhrrin-linesamp in=avhrr out=las sl=200 ss=1 nl=4000 ns=1800 bands=(1 2 4)

    AVHRRIN will convert the AVHRR archive image named AVHRR;ARCH to a LAS image named LAS;IMG. The AVHRR archive image will be windowed starting at line 200, sample 1 and will include 4,000 lines and 1,800 samples. Only bands 1, 2, and 4 will be converted.

  2. LAS> avhrrin-latlong in=[user.avhrr]usa out=[user.las]usa slat=42.5 slong=-104.0 elat=46.0 elong=-96.0

    AVHRRIN will convert the AVHRR archive image named [USER.AVHRR]USA;ARCH to a LAS image named [USER.LAS]USA. The specified latitude and longitude values will be used to calculate a window for the archive image. All bands will be converted.

  3. LAS> avhrrin-latrange in=ah11091292051432 out=las slat=44.24 elat=82.91 quadnum=2 offset=874 bands=(1)

    AVHRRIN will convert the first band of the AVHRR archive image AH11091292051432;ARCH to a LAS image named LAS;IMG. The specified latitude range that falls within the second quadrant will be selected and only 874 samples on each side of the center of the pass will be written to the output image.

  4. LAS> avhrrin-linesamp in=al11041493035110 out=s.amer comment="please mount 036190"

    Once the specified tape is mounted, AVHRRIN will find the specified image on tape, and then convert the entire image to a LAS image named S.AMER;IMG.

Description/Algorithm:

AVHRRIN converts AVHRR archive images to LAS images. The input image may be windowed one of three different ways: by line/sample, latitude/longitude, or latitude range. The input image may also be subbanded.

Ancillary data are stripped and stored in associated files. The model and ephemeris data are stored in an AVHRR Data Descriptor Record (ADDR) file (;addr). The dropped line information is stored in an ASCII file (;drpl). The HRPT minor frame data are stored in a label services file (;mnr).

For ascending passes, the image data is flipped 180 degrees so the northwest corner of the image is in the upper-left portion of the LAS image. The HRPT minor frame data, along with the dropped line data, is also flipped for ascending passes.

Nonfatal Error Messages:

  1. [avhrrin-offset] Offest too large for GAC: reset to maximum

    The offset from nadir was too large for the GAC archive image. The offset value was reset to include every sample of the image.

  2. [avhrrin-size] Number of lines/samples reset from <xxx> to <yyy>

    The number of lines/samples to include in the LAS image extends beyond the archive image. The number of lines/ samples is reset to include all of the remaining lines/ samples.

Fatal Error Messages:

  1. [avhrrin-alloc] Error allocating memory

    An error was encountered allocating memory. If the error persists, contact the system administrator.

  2. [avhrrin-band] Band <x> not present in archive image

    The specified band is not present in the archive image. Respecify BANDS.

  3. [avhrrin-eof] Unexpected EOF encountered

    The end of the archive image was encountered prematurely. Check to ensure the image is as large as the archive header indicates.

  4. [avhrrin-fatal] Fatal error encountered

    A fatal error was encountered. The message displayed preceding this message was the error encountered. Processing terminates.

  5. [avhrrin-open] Error opening <xxxxx> file

    AVHRRIN was unable to open the specified file. Check the access privileges in the output directory.

  6. [avhrrin-positive] The number of lines/samples <xxx> must be positive

    AVHRRIN calculated a negative number of lines/samples to be included in the LAS image. Ensure the latitude and longitude values were specified correctly.

  7. [avhrrin-start] Starting line/sample must be less than <xxx>

    The starting line/sample was greater than the number of lines/samples in the archive image. Respecify the parameters so the starting line/sample is less than <xxx>.

  8. [avhrrin-write] Error writing to <xxxxx>

    An error was encountered while writing to the specified file. Check the amount of disk space available.

User Notes:

  1. The quadrants are defined by the axis at the equator (zero latitude) and the meridian of Greenwich (zero longitude).

                      Greenwich
                (0 degrees longitude)
                          |
                          |
                    2     |    1
                          |
               -----------|-----------        Equator
                          |            (0 degrees latitude)         
                          |
                    3     |    4
                          |
                          |
    

    When an area of interest crosses more than one quadrant and doesn't cross either of the poles, the quadrant number should be set to the quadrant over the area of interest that the satellite first encounters. When the quadrant number is set to any quadrant (5), the image will be windowed at the starting and ending latitudes first encountered.

    As an example, assume a pass crosses the North pole and starts in quadrant one. QUADNUM must be used to specify one of three possible ranges of interest if the user requests a latitude range of 80 to 85 degrees. The range that extends five degrees from 80N to 85N before the satellite reaches the pole (QUADNUM = 1), the range that extends five degrees from 85N to 80N after the satellite passes the pole (QUADNUM = 2), or the range that extends 15 degrees from 80N before the satellite reaches the pole to 85N after the satellite passes the pole (QUADNUM = 6).

  2. When specifying a latitude range in quadrants 1-4, the correct area may not be found if one of the latitude values falls before the beginning of the scene.

  3. If a latitude range specified for a certain quadrant is too near a pole, the correct area may not be found. The minimum latitude must be at least 8 degrees from the pole and the maximum latitude must not be closer than 2 degrees to the pole. The user may have to specify a pole crossing, starting or ending at the pole, or use some other method to find the desired line numbers.

  4. When specifying quadrant 5, ensure the latitudes fall within the boundaries of the scene. If a specified latitude falls before the scene, the algorithm will indicate that the latitude range was not found.

  5. Information about the archive image can be determined by displaying the archive header file ";ahdr". This file can be displayed using the VMS 'type' or UNIX 'more' commands or DSPAHDR may be ran to get a formatted report. If the image is stored on tape and the header file is to be displayed, READARCH must be executed to first copy the image to disk.

  6. When an ascending pass is processed, the dropped lines listed in the ";drpl" file are relative to the LAS image. Thus, the dropped lines will no longer relate to the AVHRR archive image.

  7. When COMMENT is specified, the AVHRR archive image will be read from tape. When COMMENT is not specified, the image will be read from disk.