User's Guide

REATMO

Reprocess a global composite to apply atmospheric correction

Function:

Reprocess existing global composites to apply atmospheric correction to AVHRR bands 1 and 2 considering water vapor effects.

Parameters:

IN
Input image. IN must specify two LAS image bands which may be of any data type. Band one must contain AVHRR channel 1 data and band two must contain AVHRR channel 2 data. The image cannot be subwindowed. The values contained within IN must represent calibrated AVHRR data, such as that produced by AVHRRCAL. NOTE: If the two specified bands are not within the same image, REATMO will copy them into a temporary two-band image (thus requiring additional processing disk space).

SCALE
Scale method. Scaling method used to store IN, ANGLES, and OUT. The data type indicated in the image's DDR will be used to determine the scaling factor and offset value to use when scaling/unscaling the data.


  = GLOBAL: Global scaling
  = US:     US scaling

RADOPT
Radiance flag. Flag to indicate if IN contains radiance or reflectance values.


  = RADIANCE:    Input radiance
  = REFLECT:     Input reflectance

DATEBAND
Date band. Image containing the date band from the compositing process. This image must be the same size and in the same projection space as IN.

DATELOG
Date log. The log file associated with the DATEBAND image which specifies the scenes used to generate the composite.

PERIODS
Period name(s). The period names that were included in the composite. For example, '1995p31' for a global composite (period 31 for 1995), '008014' for a US composite (julian days 008 through 014).

ANGLES
Angles image. The image containing the necessary view angles. Three bands are expected, the first band being satellite zenith angles, the second band being solar zenith angles, and the third band being relative azimuth angles. This image may be generated using ANGINTERP. This image must be the same size and projection as IN. Subwindowing is not allowed. NOTE: If the three specified bands are not within the same image, REATMO will copy them into a temporary three-band image (thus requiring additional processing disk space).

SOLZEN
Solar zenith band. The solar zenith angles which coincide with the composite specified in IN. This band must be the same band that is specified as the second band in ANGLES.

ELEV
Elevation image. A single band image containing elevation in kilometers. The image must be in geographic projection with units of degrees.

WATERBASEDIR("/SGS4/KM1/ADAPS/IMAGES/")
Water directory. The base directory in which the water vapor climatology images are stored.

SILOBASEDIR("/DMF/EDC/AVHRR/")
Water silo directory. The base directory on the silo in which the water vapor acquisition images are stored.

OZONEBASEDIR("/SGS4/DSB1/DDPS/GLOBAL/OZONE/")
Ozone directory. The base directory in which the ozone images are stored.

WORKDIR
Working directory. The directory wherein processing will occur.

NDVI
Output NDVI image. The image containing the resulting normalized difference image computed from the atmospherically corrected AVHRR channels 1 and 2.

OUT
Output image containing the atmospherically corrected AVHRR channels 1 and 2. The output image is the same size, data type, and in the same projection as the input image specified by IN. Output values are expressed as a percentage of surface reflectance with atmospheric correction applied.

WATER
Water vapor image. The water vapor output image consisting of one band for each day used in the composite followed by the QC bands corresponding to the water bands. This image will be in geographic space.

QC
Quality control. The Quality control output image. This image is in the same size and projection as IN. This image will contain the following quality control values:


0:    Water vapor value taken from a daily
      acquisition, normal solar zenith angle
1:    Water vapor value taken from a daily
      climatology, normal solar zenith angle
2:    Water vapor value taken from a monthly
      climatology, normal solar zenith angle
3:    Water vapor value created using nearest-
      neighbor fill, normal solar zenith angle

100:  Water vapor value taken from a daily
      acquisition, extreme solar zenith angle
101:  Water vapor value taken from a daily
      climatology, extreme solar zenith angle
102:  Water vapor value taken from a monthly
      climatology, extreme solar zenith angle
103:  Water vapor value created using nearest-
      neighbor fill, extreme solar zenith angle
255:  Undefined pixel value

INWATER(--)
Input water vapor image. If specified, this image will be used instead of loading water vapor images from the water base directories. The image is expected to be in the same format as the image created by REATMO as the WATER image. The format is N water vapor bands followed by N QC bands where N is the number of days in the composite. The band sequence is:


    Band 1:   water vapor image for datelist(1)
    Band 2:   water vapor image for datelist(2)
    ...
    Band N:   water vapor image for datelist(N)
    Band N+1: QC image for datelist(1)
    Band N+2: QC image for datelist(2)
    ...
    Band 2*N: QC image for datelist(N)

Datelist is a list of dates returned from REATMOINFO.

SAVECOMPH2O(--)
Composite water vapor image. If specified the composite water vapor image will be saved.

Examples:

  1. LAS> reatmo in="[ddps]compimg" scale=global radopt=radiance dateband="[ddps]dateimg" datelog="[ddps]datefile;txt" periods=("1995p31") angles="[ddps]angimg" elev="[ddps]demimg" waterbasedir="[ddps.global]" silobasedir="/ddps/global" ozonebasedir="[ddps.global]" workdir="[ddps.reatmo]" ndvi="[ddps]newndvi" out="[ddps]newcomp" water="[ddps]newh2o qc="[ddps]newqc"

    The composite 'compimg' is to be processed using global scaling. The atmosperically corrected image will be expressed as radiance values. The date band image to be used is 'dateimg', the coinciding date log file is 'datefile;txt'. All images in period '1995p31' referenced in 'datefile;txt' are presumed to have been used in the composite. All intermediate files will be written to the working directory '[ddps.reatmo]'. The atmospherically corrected AVHRR bands 1 and 2 will be written to 'newcomp'. The coinciding quality control bands will be written to 'newqc'. The new ndvi band generated from 'newcomp' will be written to 'newndvi'. The water vapor bands used to atmospherically correct the data will be returned in 'newh2o' (one band for each day used in the composite).

Description/Algorithm:

Get all the relevant information from the date log file. Get a TOVS water vapor image for each day within the composite (in geographic space). Generate an elevation band, a 'line' band and a 'sample' band (all in composite space). The 'line' and 'sample' band will be used as an index into the water/ozone images in geographic space. Generate the water vapor image, ozone image, and QC band (all in the composite projection space). All of the required input files are now available and atmospheric correction is applied to AVHRR channels 1 and 2. The NDVI band is regenerated, since AVHRR channels 1 and 2 have changed. All intermediate image files are deleted once they are no longer needed (to minimize the amount of disk space required).

Nonfatal Error Messages:

    None

Fatal Error Messages:

  1. [reatmo-info] Error retrieving date log information

    An error occurred extracting the necessary information from the date log file. Ensure that the log file has been correctly specified.

  2. [reatmo-tovs] Error generating water vapor images

    An error occurred generating the water vapor images in geographic space. Ensure that the parameters to GETWATER have been specified correctly.

  3. [reatmo-elev] Error generating DEM/line/sample bands

    An error occurred generating the DEM/line/sample bands in composite space. Contact the system administrator if this error persists.

  4. [reatmo-ozon] Error determining ozone images

    The ozone image specification was not successful. Ensure that the expected ozone images reside in OZONEBASEDIR.

  5. [reatmo-comp] Error generating water/ozone/qc bands

    An error occurred generating the water/ozone/qc bands in composite space. Contact the system administrator if this error persists.

  6. [reatmo-del] Error deleting intermediate files

    The intermediate files could not be deleted as expected. Contact the system administrator for further assistance.

  7. [reatmo-jdat] Error estimating julian date

    An error occurred estimating the composites julian date. Contact the system administrator for further assistance.

  8. [reatmo-atmo] Error applying atmospheric correction

    An error occurred while applying atmospheric correction to AVHRR channels 1 and 2. Contact the system administrator if this error persists.

  9. [reatmo-norm] Error regenerating the NDVI band

    The NDVI band could not be regenerated. Contact the

  10. [reatmo-h2o] Error generating water vapor image

    An error occurred generating the image specified in WATER. Contact the system administrator if this error persists.

  11. [reatmo-fatal] Fatal error encountered

    A fatal error was encountered. Refer to the preceding error message for specific details.

User Notes:

  1. Once the water vapor image is created (parameter WATER) you may specify that image as the INWATER image on any subsequent run of REATMO for the same IN image(s) and PERIODS.