Carbon Consequences. Biomass. Atmospheric source. Biologic C Flux. Regrowth Dominated. area histograms. Disturbance Dominated. Balanced. Action: Map forest disturbance (harvest, insect damage, storm damage, fire, etc) across a Landsat frame (timing, intensity, location) for 1984-2005.
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Action: Map forest disturbance (harvest, insect damage, storm damage, fire, etc) across a Landsat frame (timing, intensity, location) for 1984-2005
Why? Interested in knowing forest carbon flux for North America, and how it is changing
Disturbance rate ->
Forest age ->
Annual or Biennial Image
Time Series (1972-2004)
Disturbance history / stand age
~25 Sample Sites
Search for leaf-on, cloud-free annual images for a given location; optimize scene selection for anniversary dates.
Need to balance:
- cloud avoidance
- data quality (e.g. L7 vs L5)
- year selection
Download/buy data (Landsat-7 data now free; Landsat-5 by end of year)
III. Orthorectify images to map base using GLS data set and SRTM digital topography; clip images to common X-Y spatial domain
- image-image registration essential; orthorectification desirable (facilitates GIS integration with other data)
IV. Calibrate each image to radiance, and apply atmospheric correction to convert images to surface reflectance
- not essential for change detection, but useful for additional studies (e.g. integration with other sensor data; canopy reflectance modeling)
Orthorectified (2) SRTM digital topography; clip images to common X-Y spatial domain
Landsat 1Gs (2) SRTM digital topography; clip images to common X-Y spatial domain
100 km SRTM digital topography; clip images to common X-Y spatial domain
1990’s Landsat-5 mosaic
BOREAS Study Region
(b) Disturbance visual inspection or automated histogram thresholding; obtain mean reflectance and standard deviation for this set of pixels, for each scene
(a) Permanent forest
Year index (19xx)
(e) Permanent non-forest
Time Trajectories of Forestness Index
Indicate Forest Dynamics
VII Use rule-based system and thresholds to identify disturbance events (e.g. “if FI increases > 8 and stays >6 for at least three consecutive years, then mark Year 1 as disturbance”).
- agriculture identified by frequent large changes in FI value
- clouds can be identified as large “single event” changes in FI
VIII. Filter maps using sieve filter to remove speckle (single pixel changes).
Fig. 1. (a) Location of samples selected across the conterminous United States, where biennial time
series stacks of Landsat images (LTSS) were acquired and analyzed to map forest disturbance
over the past three decades. The background forest group map shows that most of the forest
groups in the United States have been represented by the samples. (b) An example disturbance
map developed using the LTSS in a 28.5-kilometer-square area south of Lake Moultrie in South
Carolina. Persisting forest, nonforest, and water are shown in green, gray, and blue, respectively. All
other colors represent changes mapped in different years. (c) Percent of forest land disturbed annually,
calculated according to the derived disturbance map for the entire South Carolina Landsat scene.