New Landsat 7 Gapfilled Products

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New Landsat 7 Gap-filled Products

• Background, Plans and Status

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Overview

• Background
• Scan Line Corrector (SLC) Failure
• Current SLC-off Products
• Local linear histogram matching
• Plans for Additional SLC-off Products
• Additional Information

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Successful Launch on April, 15 1999 From
Vandenburg, CA
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ETM Optical Layout
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L7 ETM Spectral Coverage and Ground Sample
Distance (GSD)
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Scan Line Corrector (SLC) Failure

• The SLC is an electromechanical device that
  rotates secondary mirrors through an angular
  range of /-1 deg during a single scan of the
  primary mirror and corrects the image data for
  the forward motion of the spacecraft
• On May 31, 2003 the SLC halted and stopped
  rotating /- 1 deg
• The SLC halt anomaly began during the acquisition
  of path 076 row 013
• Without the SLC, the ground-track of the image
  data covers a zig-zag pattern on the ground that
  has gaps
• The direct cause of the anomaly is believed to be
  a mechanical jam preventing rotation of the SLC

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SLC compensates for the forward motion of the
spacecraft
Red regions are areas of non-coverage without SLC
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ETM SLC-off Data

• ETM data collected with the SLC-off is affected
  by areas of under and over sampling at the edges
  of scene
• These gaps represent a data loss of 25 for any
  given scene
• The center portion (22 km) of the standard
  product remains relatively unaffected by the SLC
  failure
• L7 is still acquiring 75 image data with the
  failed SLC
• USGS/EROS Data Center (EDC) released L7 ETM
  SLC-off data products on 10/22/2003
• This product is available for all L7 ETM SLC-off
  data collected from 7/14/2003 to present,
  excluding a 2-week test interval from 9/3/03 to
  9/17/03

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P33/R27 L0R Band 8
ETM Scan Line Corrector Anomaly
P36/R37 L0R Band 3,2,1
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ETM Standard L1G SLC-off Product
Rodeo-Chediski Fire Arizona Path 36/Row 36
Burn Scar
22km
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New Product Development Strategy

• In Phase I
• SLC-on to SLC-off gap-filling
• In Phase II
• SLC-off to SLC-off gap-filling

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Phase I Specifics

• Implement a L7 SLC-on to SLC-off Gap-filled
  product
• During product ordering, let users choose the
  number of interpolation pixels used during Level
  1G processing
• Enhance existing browse to show the location and
  severity of artifacts in L1G data
• Include gap pixel mask with Level 1G products

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Phase I Product SLC-on to SLC-off Histogram
Matched Previous-year Scene using Localized
Linear Methodology

• Histogram matching is a simple procedure used to
  correct striping or banding in imagery, and it
  can be applied in a similar fashion to fill the
  scan gaps in SLC-Off data
• The image histogram describes the statistical
  distribution of image pixels in terms of the
  number of pixels at each Pixel-intensity (DN)
• The linear histogram matching methodology
  attempts to find a linear transformation between
  two images
• The histogram matching method requires
  co-registered L1Gs products of both the SLC-Off
  scene and an SLC-on Anniversary scene

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Phase I Product SLC-on to SLC-off Histogram
Matched Previous-year Scene using Localized
Linear Methodology
Reference Scene (Y) Anniversary Scene (X)
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Phase I Product SLC-on to SLC-off Histogram
Matched Previous-year Scene using Localized
Linear Methodology
The gain and bias can be calculated using the
mean and standard deviation of arrays X and Y
G the gain used to histogram match the
anniversary image to the reference image B the
bias used to histogram match the anniversary
image to the reference image X the anniversary
(SLC-On) scene array Y the reference (SLC-Off)
scene array
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Phase I Product SLC-on to SLC-off Histogram
Matched Previous-year Scene using Localized
Linear Methodology

• In the 30 meter bands (Bands 1-5 and 7), the SLC
  gap is a maximum of 14 pixels wide
• A 17 pixel wide window was chosen as the minimum
  desirable window width
• In this 17 pixel square window, the data is
  collected from both the anniversary scene and the
  reference scene
• Appropriate exclusions are made, the corrective
  gain and bias are calculated and applied to the
  center pixel value from the anniversary scene
• The resulting value is used to fill the missing
  pixel in the reference image

Localized linear histogram Matching Window in
the scan gap
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Location Path36Row37SLC On7/7/2002SLC
Off6/24/2003
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Location - Path36 Row37
Standard L1G Product
Localized Linear Gap-filled
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Phase I Product- Path 36 Row 37 (center- Bands
3,2,1)
Standard L1G Product
Localized Linear Gap-filled
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Standard L1G Product
Localized Linear Gap-filled
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Standard L1G Product
Localized Linear Gap-filled
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Standard L1G Product
Localized Linear Gap-filled
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Standard L1G Product
Localized Linear Gap-filled
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Phase I User-Selectable Interpolation
14-pixel
0-pixel
14-pixel
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Standard L1G Product
Localized Linear Gap-filled
14 Pixel Interpolation
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Standard L1G Product
Localized Linear Gap-filled
14 Pixel Interpolation
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Phase I Products - zoom
Standard L1G Product
14 Pixel Interpolation
Localized Linear Gap-filled
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Standard L1G Product
Localized Linear Gap-filled
14 Pixel Interpolation
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Standard L1G Anniversary Product
Standard L1G Product
14 Pixel Interpolation
Localized Linear Gap-filled
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Standard L1G Product
Standard L1G Anniversary Product
14 Pixel Interpolation
Localized Linear Gap-filled
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Phase I Modified Browse
Numerical Scale Shows Scan Gap Width for Standard
L1G Products with 2 Pixel Interpolation
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Phase I L1G Gap Pixel Mask
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Future Tasks

• SLC-off to SLC-off gap-filled products
• Additional SLC-off Browse Product
• Cloud Pixel Mask

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Future SLC-off Browse Image
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Additional Information

• Landsat 7 SLC-off products information
  http//landsat7.usgs.gov/slcRelease.php
• Sample Data
• http//landsat7.usgs.gov/slc/sample.php
• Landsat 7 Science Data Users Handbook
• http//landsat.gsfc.nasa.gov/cgi-bin/rirish/searc
  h/search2.pl
• Landsat 7 Technical Documentation
• http//landsat7.usgs.gov/resource.html

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Contact Information
Gyanesh ChanderUSGS/EROS Data Center
(EDC)Phone [phone]Email
gchander_at_usgs.gov