Mapping the shallow marine benthic habitats of Rottnest Island, Western Australia

The introduction of new, high resolution hyperspectral sensors has led to growing interest in the development of techniques to utilise data from these instruments for mapping the shallow marine environment. The increased spectral resolution of the hyperspectral sensors allows the use of the unique spectral signatures of the individual habitat components to identify these components within the image. Hyperspectral data also allows for the mapping of habitats in shallow areas that are inaccessible to other methods such as hydro-acoustic mapping. The coastal waters surrounding Rottnest Island, Western Australia, provide a unique opportunity to apply hyperspectral imaging techniques in a temperate environment because of the oligotrophic conditions maintained by the Leeuwin Current. The shallow marine benthic habitats of Rottnest Island Reserve have been mapped to a depth of ~15 m, using spectral signatures contained in a library created from in-situ measurements of the dominant habitat components. Three lines of HyMap hyperspectral data flown for the Rottnest Island Reserve in April 2004 were corrected for sunglint, atmospheric effects and the influence of the water column using the Modular Inversion and Processing System which requires no inputs from parameters measured in the field. A decision tree based classification scheme which utilises a range of spectral similarity measures was used to map the different habitat components identified in the bottom reflectance image and the results were validated in the field using SCUBA divers. The shallow subtidal habitats found around Rottnest Island are generally dominated by either bare sand, reef with large macroalgae, such as Ecklonia radiata and Sargas-sum spp., or a number of different seagrass species. These new hyperspectral imaging techniques provide a platform for the mapping of shallow marine benthic habitats over a broad area, at a scale that is relevant to marine planners and managers

Mapping the marine benthic habitats of Ningaloo reef lagoon

Effective management and monitoring of large marine protected areas requires detailed baseline data on distribution of benthic habitats (as a surrogate for marine biodiversity). Large areas with complex bathymetry and very clear waters such as the Ningaloo Marine Park (NMP) naturally lend themselves to the application of optical remote sensing as a means of gathering data on substrates and depth

Mapping habitats and biodiversity of Ningaloo Reef lagoon using hyperspectral remote sensing data. In Waples, K and Hollander, E. Ningaloo Research Progress Report: Discovering Ningaloo – latest findings and their implications for management

This project is part of the CSIRO Flagship Wealth from Oceans, Ningaloo Cluster: “Reef use, biodiversity and socio economics for integrated management strategy evaluation of Ningaloo”. This project is run from Murdoch University in collaboration with Curtin and Queensland Universities. Airborne hyperspectral data have been acquired by HyVista through the efforts of AIMS and sponsored by BHP Billiton. The project is focusing on the mapping of habitats and biodiversity of the Ningaloo Marine Park. This is being achieved through a combination of state-of-the-art hyperspectral remote sensing techniques, coupled with biodiversity field surveys of the area

A hyperspectral, remote-sensing approach to spectral discrimination of marine habitats at Ningaloo Reef, Western Australia

Optical remote-sensing techniques, especially hyperspectral sensors, provide an non-invasive and cost-effective approach to mapping and monitoring the condition of reefs over large areas because of their capability to identify reef components on the basis of their spectral response. The aim of this study is to develop a reliable and repeatable procedure for mapping submerged coral reefs using airborne hyperspectral data. Spectral reflectance of corals, macro-algae and sediment were measured underwater with an OceanOptics2000 spectro-radiometer. These spectra were used for development of algorithms for automated applications to image classification. A genetic algorithm technique was used to determine optimal waveband combinations (including derivatives) for identification of substrate types. Initial results show that in situ reflectance spectra of reef substrates were significantly different for various spectral wavelengths. Using a linear discriminant analysis, the in situ spectra of six benthic groups (branching, digitate and tabulate Acropora, massive corals (e.g. Porites), submassive corals (e.g. Pocillopora) and macro-algae) could be classified to 90 % accuracy with as few as six bands. A classification of major habitat groups was applied to airborne hyperspectral data from HyMap acquired in November 2005 and April 2006 over the Yardie Creek area at Ningaloo Reef. The images were corrected for atmospheric, air-water interface and water column effects using the Modular Inversion & Processing System. This removes subjectivity from the classification and approaches an automated classification allowing for improved transferability to other reefs and monitoring applications. The retrieved bottom albedo image was used to classify the benthos, generating a detailed map of benthic habitats, followed by accuracy assessment. The outputs of multi-temporal image analysis contain percent cover of corals, macro-algae and sediment. Results indicate that the spectral response of corals can be determined to 10 m depth and shows that hyperspectral remote sensing techniques offer great potential in mapping coral reefs

Mapping habitats and biodiversity of Ningaloo Reef lagoon using hyperspectral remote sensing data

This project is focusing on the mapping of habitats and biodiversity of the Ningaloo Marine Park. This will be achieved through a combination of state-of-the-art hyperspectral remote sensing techniques, coupled with biodiversity field surveys of the area. Airborne hyperspectral data were collected by HyVista in April 2006 over 3500 km2 covering the whole Ningaloo Marine Park. This is the largest hyperspectral coral reef survey to date in the world and provides images in 3.5 m spatial resolution for a 1km wide terrestrial coastal strip and out to 20m depth over lagoon areas. Hyperspectral remote sensing data are corrected for atmospheric, air water interface and water column effects. This, physics-based approach, promotes automatisation and the removal of subjectivity from the classification process, allowing improved transferability to additional sampling locations and extension of the monitoring to other seasons. Field work was carried out to support the airborne data acquisition in 2006 and 2007 collecting underwater field spectra, echo-sounding data and underwater photographs to allow for accurate validation and interpretation of hyperspectral data. Field spectra from various habitats are used to characterise their spectral features enabling differentiation and classification of various bottom cover types. Transects across coastal vegetation were also conducted to identify the vegetation types and key landforms contributing to the variability in the images along the coast. Over the next three years, this project will use the hyperspectral data to develop a high-resolution characterisation of the reef, shallow water habitats and terrestrial vegetation of the coastal strip in order to support sound conservation and management of the Ningaloo Marine Park

Making sense of hyperspectral, remotely-sensed data for habitat mapping in Ningaloo Marine Park, Western Australia

Globally, hyperspectral surveys are emerging as a particularly useful technology for mapping connected benthic habitats over large areas of optically clear coastal water. Airborne hyperspectral data covering Ningaloo Marine Park are currently being used to map benthic habitats and develop a reliable and repeatable procedure for this operation. The HyMap data, at wavelengths from visible to near infrared in 126 spectral bands, covered 3 400 km2 at 3.5 m spatial resolution over the terrestrial coastal strip and out to 20m depth over lagoon and reef areas. The data were corrected for atmospheric, air-water interface and water column effects using the physics-based Modular Inversion and Processing System. This approach allowed for quantitative and automated steps, as well as the removal of subjectivity from the classification process. Fieldwork was carried out to support the interpretation, classification and validation of the bottom reflectance data. Spectral reflectance of corals, macro-algae and sediment from several habitats were measured underwater with an Ocean Optics 2000 spectroradiometer and used for development of algorithms for automated image classification. Based on linear discriminant analysis, the in situ spectra of six benthic groups (branching Acropora, digitate Acropora, tabulate Acropora, massive corals (e.g. Porites), submassive corals (e.g. Pocillopora) and macro-algae) could be classified to 90 % accuracy using as few as six optimally-positioned bands in the visible wavelengths. Hyperspectral image analysis of the Ningaloo Marine Park has confirmed that at least 16 major, cover-forming, benthic habitat categories are spectrally separable. Outputs of image analysis include percent cover and probability of these various habitat components to a depth of 15 m. Our results show that hyperspectral remote sensing techniques offer an efficient and cost-effective approach to mapping and monitoring coastal habitats over large, remote and inaccessible areas which are typical of Australia’s vast marine domain

Mapping the habitats and biodiversity Of Ningaloo Reef, Western Australia using hyperspectral imagery

The largest hyperspectral survey of a coral reef (3400 km2) was undertaken in April 2006 and forms the core data set for mapping habitat components and biodiversity of the Ningaloo Marine Park, Western Australia. Optically deep waters of this region are ideally suited for remote sensing techniques and airborne data were collected by HyVista. The data are at 3.5 m spatial resolution for a 1km wide terrestrial coastal strip and out to 20m depth over lagoon and reef areas and covers wavelengths from visible to near infrared at 15nm intervals. Hyperspectral data were corrected for atmospheric, air-water interface and water column effects using the physics-based Modular Inversion & Processing System. This approach allows for quantitative and automated steps as well as the removal of subjectivity from the classification process, allowing improved transferability to additional sampling locations, field spectral datasets and extension of the monitoring to other seasons. Underwater field spectra were collected using an OceanOptics spectrometer as well as underwater photographs, to allow for accurate interpretation and validation. Results of this mapping can be compared to the transect data collected by divers from other studies and also to earlier habitat maps prepared by expert interpretation of aerial photography. Comparisons of classification results for Coral Bay area show promising results in the discrimination of branching, tabulate and massive corals as well as macro-algal assemblages. Remote sensing offers unique tools which are non-invasive, quantitative and enable mapping of large areas into a seamless data set which can be integrated with human use data, oceanographic circulation models and other spatial data sets. The hyperspectral data are being used to develop a high-resolution characterisation of the entire reef, shallow water habitats and terrestrial landforms of the coastal strip in order to support sound conservation and management of the Ningaloo Marine Park

Habitats and biodiversity of Ningaloo Reef Lagoon, Western Australia

As part of the CSIRO Wealth from Oceans Ningaloo Collaborative Cluster programme currently underway in Western Australia, this study aims to examine lagoonal habitats and biodiversity within Ningaloo Reef. Key habitat types were identified using information from hyperspectral remote sensing and were used to develop a stratified sampling approach. Two focal areas were selected, based on sanctuary zones within Ningaloo Marine Park: Osprey Bay and Coral Bay in the north and south respectively. A nested quadrat sampling regime was used to attempt to link field-collected data with remotely-sensed data, collected at different scales. Preliminary results confirm that northern sections of Ningaloo Reef differ greatly from the south, with a greater diversity of habitats present in the broader lagoons in the south. Greater areas of coral are found close inshore and across the entire reef at the southern location, compared with the northern section, which has a broad expanse of sand and limestone pavement before grading to corals further offshore (back-reef and reef-crest). These differences in habitat may have implications for the overall biodiversity of the two locations and more broadly along the reef