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Land Cover Analysis: Hawaii Land Cover
Land Cover Change Summary
Data Development Methods
Hawaii Project Poster
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Land Cover Analysis

Data Development Methods

Study Area Definition and Image Acquisition

  • Project focus centered on the eight main Hawaiian Islands [camera icon to denote a link to a pop-up picture window] including Niihau, Kauai, Oahu, Molokai, Lanai, Maui, Kahoolawe, and Hawaii.
  • Landsat 7 Enhanced Thematic Mapper (ETM) imagery was used.
  • Land cover change requires two dates of imagery to make a comparative assessment. Due to the lack of historical data from Landsat Thematic Mapper 4 and 5, it was not possible to perform a change analysis.
  • Imagery was ordered from the EROS Data Center (EDC), georeferenced in Albers equal area projection.

Create Cloud-Free Composite

  • Cloud-free satellite imagery is preferred when doing a land cover analysis because clouds obscure surface areas, making it difficult to accurately identify what lies beneath.
  • Hawaii is characterized by almost constant cloud cover. To minimize cloud cover, multiple image dates and scenes [camera icon to denote a link to a pop-up picture window] were used to map each island. In some cases, no clear imagery was available for portions of the land surface.
  • To get a clear picture of Hawaiian land cover it was necessary to combine multiple pieces of cloud-free images to form a cloud-reduced image mosaic.
  • A band ratio technique was used to identify clouds and cloud shadow areas and mask them out of the imagery. After removing these clouds, cloud-free pieces of overlapping images were reinserted into these holes, forming a cloud-reduced mosaic.
  • Even though multiple images and scenes were used to piece together a cloud-free mosaic, the final cloud-reduced imagery is still characterized by 10 to 15 percent cloud cover.

Initial Data Development/Signature Development

  • The islands were broken into classes of major land cover features such as developed, cultivated land, grassland, forest, scrub lands, wetland, bare land, and water.
  • These land cover classes were further refined into the Coastal Change Analysis Program (C-CAP) land cover classes, developed for the contiguous USA.
  • Draft products for the islands of Oahu and Maui were classified prior to field visits. For the six remaining islands, only the initial clustering or general identification of land covers was completed prior to visiting the islands.

Field Visits

  • Field visits and the collection of ground reference data are essential components of any land cover classification. This step allows analysts to visit areas of uncertainty or confusion that they encountered in the initial classification and determine if their preliminary identification of land cover classes was correct.
  • Project partner expertise and local knowledge was a critical component in the characterization of land cover for Hawaii. Analysts met with project partners, who provided local expertise and access to state, federal, agricultural, and closed lands, as well as to reserves.
  • Project partners accompanied Center staff and assisted with the completion of aerial and ground surveys of the eight main islands. Aerial surveys [camera icon to denote a link to a pop-up picture window] played a crucial role as many areas were inaccessible via ground transportation.

Final Image Processing

  • During the final land cover class development, many map products were sent to project partners in Hawaii so that they could assist with accuracy and class confusion issues.
  • Project partners were able to guide Center staff with classification issues by examining classes and identifying land cover areas as right or wrong.

Final Accuracy Assessment (field work trip)

  • For each island, Center staff generated stratified random samples of field points to visit and verify. Center staff then made coordinated field visits to examine as many points as possible.
  • Center staff utilized an interactive laptop and Global Positioning System interface for accuracy point verification. This process uses the satellite imagery as a visual backdrop to aid Center staff as they navigate to each point and examine whether that point has been correctly classified on the satellite imagery.
  • Due to their expertise and local knowledge of both the area and land cover found throughout the Hawaiian Islands, project partners again assisted with the final ground and aerial surveys.
  • Throughout the final accuracy assessment, Center staff identified what could be improved upon, and noted any errors in the land cover classification, which were then corrected.

Final Products

C-CAP land cover for the main eight Hawaiian Islands. These data sets are available individually for downloading. A cloud-reduced mosaic in poster format is also available.