AUTHOR: Tim Baltzer
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.
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.
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:
- Option 1: Use a mean water vapor image. From a scientific perspective, water vapor has a strong influence on the correction algorithm and using an average would bias the results significantly (therefore not a good solution).
- Option 2: Modify GETATM to accept 16 water vapor images, 2 ozone image, and the date band from the composite. This would require almost a complete rewrite of GETATM (1-2 man-months) of work.
- Option 3: Modify GETATM code (1-2 man-days) to write two additional bands which would be the line/sample coordinates from the water vapor and ozone images instead of the actual values. Create a separate process (1-2 man-weeks) that would take the line/sample bands, the date band from the composite, the 1-16 daily water vapor images and 1-2 ozone image and create an image containing the correct water vapor and ozone values for the specific day of each pixel.
for each pixel doend for
- Read the date band to determine which AVHRR image it came from, to determine the acquisition date, to determine:
- which TOVS image to read from (one for each compositing day)
- which ozone image to read from (one ozone image per month, composite may span a month)
- Read the line/sample band generated by GETATM to determine which line/sample to read from the appropriate water vapor/ozone images.
- Read the appropriate pixel from the appropriate water vapor and ozone image.
- Write the water vapor and ozone pixel to the output image (same space as the date band).
- NOTE: For a pixel in an undefined region, the date band will contain a mask value of '2' (global scaling technique used). In this event, the output water vapor value, ozone value, and quality control value must reflect this 'undefined' status (values tbd).
- 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.