SLC Gap-Fill Methodology 1/5 3/18/2004
SLC Gap-Filled Products
Phase One Methodology
Pat Scaramuzza, Esad Micijevic, Gyanesh Chander
Introduction:
The Landsat 7 scan-line corrector (SLC), a mechanism designed to correct the
undersampling of the primary scan mirror, failed on May 31, 2003. With the SLC now
permanently turned off, the ETM+ is losing approximately 22% of the data due to the
increased scan gap. This paper describes a local linear histogram matching technique
which will be used initially to fill the scan gap with previously acquired Landsat 7
imagery.
Methodology:
Filling the scan gap first requires precise knowledge of what pixels are valid in an image
and which are to be filled. To do this a scan gap mask is created for each band that marks
existing data as 1 and missing data in the scan gap and fill regions as 0. These scan gap
masks are created during L1G product creation by a second pass through the same
resampling algorithms used to create the L1G product. They are delivered with the
product as 8-bit images having dimensions identical to the corresponding image band
files, and are compressed using the gzip utility to avoid expanding the product size.
Once the gaps are located, the linear histogram matching methodology attempts to find a
linear transformation between one image and another.
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Anniversary scene
L1Gs Radiance (DN)
Reference scene
L1Gs Radiance (DN)
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Anniversary scene
L1Gs Radiance (DN)
Reference scene
L1Gs Radiance (DN)
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Y ≈ GX + B
Figure 1: An assumed linear relationship between scenes
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