Mapping coral reef environments

Abstract

Coral reef environments support high levels of marine biodiversity, they are important sites for coastal habitation and they provide a range of goods and ecosystem services such as nearshore fisheries, economic revenue from tourism and breeding sites for seabirds and turtles. Mapping is a fundamental activity that underpins our understanding of coral reef environments and helps to shape policies in resource management and conservation. This is particularly the case for quantifying the area of landcover types associated with reef environments, including coral patches, seagrasses and mangroves, but also for monitoring how these change over time and modelling how spatial patterns apparent on reefs are related to environmental drivers. Field techniques and aerial photography have historically played a crucial role in mapping coral reef environments, which has recently seen a transition toward the processing of satellite remote sensing images. This paper examines a series of maps produced of Low Isles, the most mapped island on the Great Barrier Reef, to review historical methods for mapping coral reefs because of the critical importance of understanding how past maps were made, which determines appropriate uses to which they can be put. Recent advances and future opportunities for the application of mapping technologies to coral reefs are also evaluated, including the use of unmanned aerial vehicle (UAV) platforms for airborne surveys, delivery of information through web-based platforms and improvements in the quality of information for making and presenting maps. Maps have transformed the way we have responded to both historic and contemporary coral reef problems. This timely review communicates how maps, and the fast growing technologies that are employed to produce them, are central to our understanding of coral reef environments. Recent advances that may drive exciting new environmental management tools are identified.

Assessing Reef-Island Shoreline Change Using UAV-Derived Orthomosaics and Digital Surface Models

“…Reef islands were historically mapped using a range of methods, including plane table surveys on the islands of the Great Barrier Reef in the 1920s, pace and compass surveys, and theodolite triangulation [11]. More recent studies analysed changes to island configuration and planform area by digitising shorelines from georeferenced aerial photos or satellite imagery [12][13][14].…”

“…The extent to which planimetric change correlates to volumetric change on reef islands is not yet known; this requires detailed topographic data, yet only a small number of studies analysed reef-island beaches in three dimensions using topographic or GPS surveys [16][17][18]. Spatially comprehensive topographic data may be collected using light detection and ranging (LiDAR) or terrestrial laser scanners (TLS), or derived from aerial photography or satellite imagery using photogrammetry or structure-from-motion (SfM) [19][20][21]; however, these techniques can be expensive in remote areas, where most reef islands are found [11].…”

“…Several limitations to the use of UAVs were identified, including their small spatial coverage compared with satellite imagery and inability to fly where regulations prohibit or in adverse weather conditions (rain, strong wind, or excessive heat) [11]. Many jurisdictions also have limitations on the weight of UAV that may be flown without a professional licence [24].…”

“…The flight elevation and camera specifications determine the image resolution; trade-offs between desired resolution, area covered, and length of time available for the survey must be considered. Changing tide level and weather conditions (such as light and wind) throughout the period of UAV survey can also affect image quality and interpretation [11], while sun glint can affect image quality in tropical environments due to the high trajectory of the sun [33]. Furthermore, the degree of image overlap, camera angle, and SfM processing parameters can strongly influence the accuracy of geospatial outputs [30].…”

Accuracy Assessment of Alos W3d30, Aster Gdem and Srtm30 Dem: A Case Study of Nigeria, West Africa

“…are chief sources of height information which are greatly applied in many disciplines. Many areas where DEMs are applied include: flood inundation modeling Journal of Geographic Information System [1]; vegetation mapping [2] [3]; mapping of Coral Reef Environments [4]; development of Geopotential Global Models [5]; evaluation of glacier volume change [6]; navigation systems for commercial aviation [7]; climatic modeling [8]; archeology [9]; glacier surface change [10]; hydrological analysis and simulations [11]; soil science and geology [12]; Catchment Geomorphology and Hydrology [13]; and monitoring coastal erosions and sedimentations [14]. In another study, the author further categorized the various areas where global or near global DEMs can be applied [15].…”