Brief description
This data set consists of a shapefile/kml of mangrove extent and dominant species for Kakadu National Park mangroves generated from true colour aerial photographs acquired in 1991.
From true color 1991 orthomosaics of Field Island and the Wildman, West, and South Alligator Rivers, mangroves were mapped by first applying a fine scale spectral difference segmentation within eCognition to all three visible bands (blue, green, and red). A maximum likelihood (ML) algorithm within the environment for visualizing images (ENVI) software was then used to classify all segments using training areas associated with mangroves, but also water, mudflats, sandflats, and coastal woodlands. These were identified through visual interpretation of the imagery. Segmentation was necessary as 1) the diversity of structures and shadows within and between tree crowns limited the application of pixel-based classification procedures and 2) the color balance between the different photographs comprising the orthomosaics varied. All segments were examined individually and methodically to determine whether they should be reallocated to a non-mangrove class (e.g., mudflats) or confirmed as mangroves. Open woodlands dominated by Eucalyptus species could also be visually identified within the aerial photography (AP) orthoimages, although their discrimination was assisted by only considering areas where the underlying LiDAR DTM (Digital Terrain Model) exceeded 10 m, assuming this excludes tidally inundated sections.
Lineage
Progress Code: completedNotes
CreditWe at TERN acknowledge the Traditional Owners and Custodians throughout Australia, New Zealand and all nations. We honour their profound connections to land, water, biodiversity and culture and pay our respects to their Elders past, present and emerging.
Defining the spatial extents at a given point in time provides a baseline to estimate changes over time, this enables informed decisions in environmental management practises.
Data Quality Assessment Scope
local :
dataset
<p>The photographs used for the mapping (frame size of 230x230 mm) were acquired by a Wild CR10 flying at 4000 m and the resulting orthomosaics and canopy height models (CHMs) were obtained at a spatial resolution approximating 1 m, with an assumed positional accuracy of <span>±</span> 50 m. Comparison with the ground-transect data collected in 1998 from the western bank of the West Alligator River confirmed that the canopy height estimated from the aerial photographs was within and often less than 2–3 m of the ground-based estimates, noting that there was a 7-year lag in the observation time.</p>
<p>Details are provided in <a href="https://doi.org/10.1071/MF17065"> Lucas et al., 2017</a>.</p>
Data Quality Assessment Result
local :
Quality Result
As neither finer spatial resolution airborne nor field data were acquired at the time of the airborne data acquisitions, the accuracy of the classifications could not be easily quantified. However, the refinement through visual interpretation provided a high level of confidence in the maps of mangroves derived from the segmented AP. To indicate the accuracy of the refined classification, 400 segments were randomly chosen and their assignment was assessed visually against interpretations of the original data. Overall accuracy of 92% was obtained for the AP classifications of mangrove and non-mangrove (e.g., saltmarsh and sediment).
Created: 2022-02-03
Issued: 2022-02-10
Modified: 2024-09-29
Data time period: 1991-03-01 to 1991-03-01
text: Field Island and the Wildman, West, and South Alligator Rivers
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Point-of-truth metadata URL- URI : geonetwork.tern.org.au/geonetwork/srv/eng/catalog.search#/metadata/0e62131b-dee1-4ac4-b273-af9cc21b4ae5
- global : 0e62131b-dee1-4ac4-b273-af9cc21b4ae5
