Landsat-8 and ASTER Comparisons for Tacloban City

NASA provides high spatial resolution sensors that can be used to identify significant areas of urban, land surface, and coastal change following disasters.  SPoRT is investigating the use of this type of imagery for the analysis of tornado and hail damage tracks within the continental United States, but has also obtained imagery (via the USGS Earth Explorer and Hazards Data Distribution System) over the Tacloban City area, particularly hard-hit by Super Typhoon Haiyan.  Whereas MODIS (250 m) and VIIRS (350 m) each have a moderate spatial resolution and large swath width and view the surface a couple of times per day, ASTER and the Landsat-8 Operational Land Imager provide a higher spatial resolution (15 m, 30 m) but with less frequent collection.  Below are some examples of true color Landsat-8 imagery, similar to the interpretation of aerial photography, and a natural color image from ASTER.  Natural color imagery attempts to replicate the overall quality of a true color image with green vegetation, blue water, and grayish urban areas, but ASTER lacks the specific R, G, B visible wavelength bands required for a “true” true color image.  By comparing relatively cloud free Landsat-8 data from July and data collected today from ASTER, areas of significant change can be identified by changes in color and texture.  These correspond to surface changes, such as vegetation damage or disruption of the typical pattern of road networks due to surface debris.  In mountainous areas, there may also be indications of river flooding, though the overall darkening of pixels in the region may also be caused by cloud shadows that complicate the analysis.  NASA has several ongoing projects related to disaster analysis and response activities, extending the societal benefits of on-orbit sensors.  SPoRT seeks opportunities to leverage these assets to benefit end-user decision making, in collaboration with other NASA researchers and the broader scientific community.

Landsat-8 false color composite over the Tacloban City area from July 2013.  Red areas indicate significant vegetation, dark blues as water, clouds in white, and less vegetated or urban areas in shades of gray to cyan.

Landsat-8 false color composite over the Tacloban City area from July 2013. Red areas indicate significant vegetation, dark blues as water, clouds in white, and less vegetated or urban areas in shades of gray to cyan.

aster_false_poststorm

ASTER false color composite from November 13, 2013. Changes in color, such as changes from reds to grays, or reds to dark blues, and other changes in texture identify possible flood or damage areas following the storm when compared to Landsat pre-storm image.

landsat_haiyan_prestorm

Landat-8 true color image of the Tacloban City area acquired on July 9, 2013.

aster_natural_poststorm

ASTER natural color imagery from November 13, 2013 and some areas of  change in color and or texture versus the Landsat-8 true color imagery. Some cloud contamination (shadowing) and thin clouds or haze across the area also contributes to changes in color and reflectance. Note that natural color is an approximation of true color capabilities.

 

 

 

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