2008-01-03: SeaWiFS Data Processing

From Datafedwiki

Title: 2008-01-03:_SeaWiFS_Data_Processing
Date: 2008/1/03
Blog:SeaWiFS Processing Research Rotation Blog
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Data Processing

Data for 2005 was used for initial run to check for errors in processing. It was observed that usually the last spliced image (on the west side of US) was not corrected for rayleigh correction and also had improper splicing. (Figure Below)

Similar errors were found even when smaller domains were considered. The west-most swaths for Georgia Fires [April-May, 2007] and California Fires [Oct 2007] showed similar error. The cause of this error is not known, but by increasing the desired region from -125 West to -160 West, the processed image was found corrected. Addition of the extra region, and hence the additional image, probably caused the removal of error over the desired region. The blank space due to the increased area can be easily removed, resulting in satisfactory results over the region of interest.

The following processed images for California Fires [Oct 2007], show the effect of increasing the desired region from -125 West to -160 West

The data for 2006 was downloaded. The processing of the data for last 3 months remains to be finished.

Image:Example3.jpg

Also, the data till September 2007 has been downloaded. The data for February 07 has been processed.

Learning ENVI processing

After reading the basic information about ENVI, the following operations were tried out on the sample image (Landsat data of Canon City) provided with the software and later on the HDF file (Feb 2007):

• Loading Image: The following three windows are opened displaying intimately linked image
  • Image Box: Shows a portion of the image at full resolution. Highlights the area shown in the Zoom Box
  • Scroll Box: Displays the entire image at reduced resolution. Highlights the area shown in the Image Box
  • Zoom Box: Shows magnified view of the portion of image highlighted in the Image Box

• Cursor Location: Displays the screen values and actual data value of the pixel located underneath the cross-hair cursor in either of the three windows mentioned above.
  • Screen Value (colour): varies from 0 to 255
  • Actual Pixel Value: varies from 0 to 100

• Image Profiles: Shows variation of data value across an image line or spectral band
  • x-profile: Variation of pixel data value along x-axis for a given y-coordinate
  • y-profile: Variation of pixel data value along y-axis for a given x-coordinate
  • z-profile/Spectral profile: Variation of the reflectance with wavelength for the particular pixel in focus

• Contrast Stretching: Attempts to improve the contrast in an image by stretching the range of intensity values it contains to span a desired range of values
  • Default for the image loaded: 2% linear stretch
  • Histogram is used to control the contrast. By changing the stretching limits in the input window the stretched histogram and new images are obtained as outputs
  • Different types of contrast stretching can be applied using the built-in stretching options in "stretch-types"
    • Linear
    • Piecewise Linear
    • Gaussian
    • Equilization
    • Square root