Design Document for COMPATM

COMPATM

AUTHOR: Tim Baltzer

Functional Summary:

If atmospheric correction is to be applied to an image using ATMOCOR, associated images the same size and in the same space must be available. COMPATM will generate water vapor, ozone, and quality control images that are the same size and in the same space as some specified input image (usually a composite image). Generate water vapor and ozone image bands in the same projection and space as some specified composite image.

Background:

A new algorithm for ATMOCOR which includes correction for water vapor has been created. Consequently, there is a need to reprocess composite images using the new ATMOCOR. Since there is data from multiple acquisition days within a composite, a single water vapor image/ ozone image cannot be used as input to ATMOCOR. Also, the water vapor and ozone images reside in a different projection (Geographic) than the typical composite product (Goodes projection). A module must be written to take the line/sample information generated by GETATM and extract the appropriate water vapor/ozone values from the appropriate water vapor images and ozone image.

Comments:

Three options were considered for solving the problem of providing water vapor and ozone images for previously processed composites (required input data to atmospheric correction). Option number three is being implemented, these three options are summarized below:

Requirements:

  • Must generate a water vapor band, ozone band, and quality control band. These output bands must be the same size and in the same space as some input image (usually a composite image).
  • Read input images, all in the same composite projection and space: - Date band image - Line/sample image (2-bands) written by GETATM - Solar zenith angle band
  • Read input images, all in the 'geographic' projection and space: - input water vapor images - input quality control images - input ozone images
  • Quality control band must include flags for the solar zenith angle (flag those angle values that are greater than 70 degrees).
  • Must allow for an undefined pixel in output image (an undefined area within the Goodes projection).
  • NOTE: For an overview of the process wherein COMPATM is called, refer to the REATMO module.
  • Scope/Limitations:

  • GETATM (or compatible functionality) must have been previously executed to create a 2-band image containing line and sample data values. This image must be in the same projection and space as the composite. The line/sample values are index references into the water vapor images and ozone images.
  • Windowing of the input images is not supported, the entire images must be processed.
  • This module is to be designed to process all composites (1KM, US, AL, etc.). For that reason, two input ozone images need to be considered (some composites span a month). Also, up to 16 input water vapor images need to be considered (example: composite spanning Dec 15 - Dec 31).
  • Overall design:

    Algorithm:

    Create an index table with an entry for each day within the composite (date band value --> acquisition date).
    for each pixel do end for

    PARAMETERS:

    OZONEIN
    The 1 or 2 bands of ozone data (the ozone images are maintained in a per month format, the composite may span a month). This image must be 180 lines by 360 samples and must be in the geographic projection.

    WATERIN
    The 1-16 bands of water vapor data (one band of water vapor for each day used in the composite). These images must be 180 lines by 360 samples and must be in the geographic projection.

    QCIN
    The 1-16 bands of quality control data (each band coinciding with a water vapor band used in the composite). These images must be 180 lines by 360 samples and must be in the geographic projection.

    COMPIN
    The "date log" band from a composite image.

    SCENELIST
    List of scenes. A list of scenes as returned by REATMOINFO. A list containing the scenes used in the composite. All entries in the list with a value of "-1" signify that the scene was not used in the composite. For example, if SCENELIST(5) = -1, then we know that scene number 5 was not used in the composite. Otherwise, the positive entry is used as an index into the DATELIST array. For example, if SCENELIST(4) = 3, then scene number 4 was used in the composite, and the date of scene number 4 is stored in DATELIST(3).

    DATELIST
    A list of all the dates used in the original composite, in the format of MMDDYY. This list is usually generated by REATMOINFO (part of the REATMO module) after reading the "date band log" file.

    SOLARZENIN
    A band containing the solar zenith angle values for the composite. This image will be used to update the quality control band to include solar zenith flags. This image is usually generated during the time that the original composite was generated, or may be generated by GETATM. This image must be in the same projection space as COMPIN.

    LINESIN
    A band containing the line number to reference in OZONEIN or WATERIN. This image must be in the same projection space as COMPIN. While this image must be in the same projection space as COMPIN, it's pixel values are to be used as line indices into the OZONEIN or WATERIN bands, which are in geographic space. This band is usually generated by running GETATM.

    SAMPLESIN
    A band containing the sample number to reference in OZONEIN or WATERIN. This image must be in the same projection space as COMPIN. While this image must be in the same projection space as COMPIN, it's pixel values are to be used as sample indices into the OZONEIN or WATERIN bands, which are in geographic space. This band is usually generated by running GETATM.

    OUT
    The two-band output image containing the water vapor values (band 1) and ozone values (band 2). This output image is in the same projection space as COMPIN.

    OUTQC
    The one-band output image containing quality control values. These values are selected from the appropriate input quality control images as defined by the date band. This output image is in the same projection space as COMPIN.

    Testing criteria:

  • Test using a 1KM global composite in the Goodes projection.
  • Test using a US composite.
  • Test using a short compositing period (Feb 21-28).
  • Test using a long compositing period (Dec 21-31).
  • Test using a compositing period which spans a calendar month.