Littoral Zone Analysis


Case Study

Determining littoral zones in the Florida Keys using World View 2 Imagery

World View 2 (Source: DigitalGlobe-used with permission) image over an area in the Florida Keys near the Alligator and Davis Reefs. Over laid on the image are the Genie Pro results of the littoral zone classification.

View Imagery

Background

Genie Pro, an automatic feature extraction tool, performs supervised classification by assembling and evaluating different types of image preprocessing chains in order to automatically create an attribute space that is easily divided into classes. Genie Pro uses a library of image processing operations and a grammar-guided evolutionary algorithm to build non-linear spatial-spectral image processing chains that define a pixel attribute space in which a traditional supervised statistical classifier can learn the decision rules for each class.  Genie Pro’s spatial processing operators include both textural and morphological processing operations. Textural operators calculate neighborhood properties, such as statistics, and morphological operators apply shape-based filters to the data. The algorithm makes no assumptions about the type of imagery, and so can be used to learn algorithms for processing data from multiple sensors.

Genie Pro takes full advantage of the increased spectral and spatial resolution of DigitalGlobe's WorldView 2 imagery (Image 1). The addition of the coastal blue band (400-450nm), with its water penetration characteristics, enhances Genie Pro's ability to accurately map shallow littoral zones and near shore benthic environments. However, Genie Pro uses every band available when creating solutions, selectively using only those bands which most accurately classify the desired features.

Feature Extraction

This case study covers an area from Plantation Key to the Upper Matecumbe Key off the southern Florida coast and includes part of the adjacent Florida Bay (Image 2). Eleven different feature classes were created to represent various zones visible in the image. Zones, based on water depth and benthic environment, were distinguishable to a depth of about 20+ meters. Some obvious zones that became the feature classes for this study were, the Florida Bay, Hawk Channel, reef areas, shelf edge and the shelf slope leading to the Florida Straits. The key itself and other land areas were considered a background feature class.

Once zones were selected and training pixels added, a solution was created using Genie Pro. The solution algorithm consists of multiple image processing chains of spatial, spectral, textural and morphological filters and operators applied to the image data, followed by a classifier that decides to which class each pixel belongs. The solution is then applied to the image to produce a results overlay image (Image 3). Image 4 is an annotated version of the results image showing the major features in the area.

Two reef areas, the Alligator Reef (image 5) and the Davis Reef (images 6 and 7) were examined in greater detail. In both areas, NOAA nautical charts, superimposed on or shown beside the Genie Pro results image, are used for comparison purposes. In each case Genie Pro closely portrays the coastal environments present as depicted in the NOAA nautical charts.

Genie Pro is an effective tool to gain accurate and easily updatable information of the near shore benthic enviroments. It is especially significant when using the high spectral and spatial resolution in the WorldView 2 imagery with the water penetration characteristics of the coastal blue band. Genie Pro results images are both accurate and easily updatable which makes it an effective tool for gaining a clearer picture of near shore waterways.

Images

Image 1 - World View 2 MS image over an area in the Florida Keys near the Alligator and Davis Reefs.

Image 2 - The WorldView 2 image covers the coastal area from about the Upper Matecumbe Key northward to Plantation Key off the southern Florida coast and includes part of the adjacent Florida Bay. The Alligator Reef and Davis Reef are visible in the image.

Image 3 - Genie Pro Results image over the entire image showing the near shore littoral zones and benthic enviroments.

Image 4 - Annotated results image showing major features.

Image 5 - NOAA nautical chart used to compare Genie Pro results in the Alligator Reef area.

Image 6 - NOAA nautical chart is superimposed on the Genie Pro results image in the Davis Reef area.

Image 7 - The Genie Pro results image in the Davis Reef area

Source: DigitalGlobe World View 2 MSI Image-used with permission
Source: http://worldview2.digitalglobe.com/docs/WorldView-2_8-Band_Applications_Whitepaper.pdf, accessed 30 June 2012.
Source: http://www.nauticalflorida.com/nautical-charts/fowey-rocks-alligator-reef.html, accessed 30 June 2012
Source: http://sanctuaries.noaa.gov/pgallery/atlasmaps/images/fkeast_2000.jpg, accessed 30 June 2012.