- SPECIAL REPORTS
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Coffs Harbour in northern New South Wales, Australia, is rich with ecological beauty and diversity. Located along the coast of Australia’s eastern seaboard approximately four hours south of Brisbane, the region features an alluring combination of rugged coastline and subtropical rainforest. Like many coastal areas, the harbor has seen a significant increase in population in recent years as large numbers of city dwellers have relocated to smaller seaside communities. The region has also become an increasingly popular tourist destination--an estimated 30,000 people visit the area during the peak summer months each year.
As demand for the coastal and hinterland “paradise” increases, one of the primary roles of the Coffs Harbour City Council is to ensure that the key attractions of beach, forest and community are maintained. “Vegetation management and protection is very important in the organization’s strategic plans and practices,” says Ron Graham, the council’s GIS administrator. “The council has been at the forefront of local government habitat mapping for many years.”
In 2007, council members decided to expand their existing GIS data sets of vegetation boundaries with new high-resolution imagery. The council hoped that the project would serve as a pilot for developing new methodologies and set new standards for vegetation mapping. To capture the images and generate the improved maps, the council turned to AAMHatch, an Australian aerial survey and mapping firm, as well as Eco Logical Australia, an environmental services firm.
Spatial AccuracyThe first step in the project was to capture detailed vegetation structures and boundaries. Using a large-format Intergraph Z/I Imaging digital mapping camera (DMC), which was selected for its high-quality imagery and data adaptability, AAM Hatch collected four-band (red, green, blue and near-infrared) multispectral imagery of the 1,174-square-kilometer (453-square-mile) region at a 0.225-meter resolution. The firm also collected airborne LiDAR data at a +/-15 centimeter vertical accuracy using an Optech ALTM 3100EA airborne laser mapping system. These data were combined with the multispectral imagery to develop key inputs for vegetation mapping.
The LiDAR- and DMC-derived product was classified into six vegetation structure classes: tall trees, medium trees, low trees, tall shrubs, low shrubs and grasses/ground. “Although lacking floristic information, these images have the potential to underpin a new generation of spatially refined vegetation mapping for the local government area,” says Mark Freeburn, project delivery manager at AAMHatch.
An Integrated ApproachThe next phase of the project, which was handled by Eco Logical Australia, was to devise a methodology that would allow new data sets to be combined with the existing vegetation studies. Using maps of an area covering the Coffs Harbour airport and Boambee Beach as a pilot study, Eco Logical Australia’s Coffs Harbour office explored the potential for simplifying complex LiDAR-derived data while maintaining a satisfactory level of mapping resolution. Staff developed a matrix of LiDAR-derived structure codes and council vegetation types in which any combination that appeared compatible (e.g., medium trees and swamp forest) was assigned a “yes,” and any combination that appeared incompatible (e.g., low shrubs and open forest) was assigned a “no.”
This methodology was adequate for the pilot-study area, but issues arose when it was applied to other areas of the region with more complex vegetation. Eco Logical consulted with ESRI personnel who recommended that the size and complexity of the data be reduced. The data were then converted into a grid format with a 2-meter pixel size and then back to a polygon format. This conversion effectively reduced the number of polygons by around half, and the city council was able to proceed with thinning the data and combining the imagery.
“The LiDAR/imagery project was undertaken due to increasing demand for more accurate height data and the urgent need to address the accuracy and currency of vegetation mapping and potential climate change impacts. Although the initial investment was costly for our small local government authority, we are now saving time and money in our planning efforts,” Graham says.
Sidebar: Applying the Data
• Redefining river and creek catchment boundaries, waterway/drainage patterns and stream order (using ESRI’s hydrology tools).
• Creating “line of sight” diagrams for the council’s telemetry system, which links all of the water and sewer pump stations.
• Slope mapping.
• Updating flood studies and assessing coastal hazards.
• Evaluating the impact of climate change.
• Upgrading the cadastre. The rectified imagery is currently being used in conjunction with Clatworthy ACRES and UTM software to upgrade the accuracy of the cadastre. The new imagery highlights some significant discrepancies with the current accuracy of the cadastre (e.g., shifts of 1 to 30+ meters).