• Remote sensing techniques to monitor coral reef systems.
• Reef-scale change detection in the Middle East, Indian, Atlantic and Pacific Oceans
• Random vs. ordered deposition in tropical shallow-water carbonate environments

1) A Modular 'reef-up' monitoring strategy:
Satellite remote sensing provides a cost-effective means of mapping coral reef habitats in shallow clear waters. However, since coral environments are submerged, a successful remote sensing strategy that relies on the spectral differences between reef substrates as a means of discrimination, must be capable of correcting for the disruptive influence of the water column. Although it is possible to model depth, bottom albedo and water column properties from hyperspectral data using optimisation techniques, the broad bandwidths and relatively poor radiometric resolution of today's multi-spectral satellites preclude such an approach. I have tested a strategy whereby water column correction is implemented using an independently collected measure of bathymetry combined with radiative transfer modelling, to process the satellite imagery to units of substrate reflectance. Image classification is subsequently driven using statistics derived from in situ optical measurements and therefore independent from the imagery. A Principal advantage of this strategy is that the situ spectra can be used retrospectively to train alternative remote sensing instruments of differing spectral resolution without the need for a repeat field campaign to collect ground-truth data. In addition, the fact that field time does not have to be dedicated to the collection of ground control points for use in algorithm training, allows more time to be spent collecting data for accuracy assessment of the final map product.

2) Geospatial characteristics of modern shoal-water carbonate depositional environments:
A key feature of sedimentological research is the attempt to understand the lateral relationship between facies and whether spatial patterns are ordered and deterministic or essentially stochastic. Much of this information is encoded in spatial patterns, visible in sequence thicknesses or lateral extent. Recent carbonate depositional systems, can serve as analogues to comparable ancient systems, assist facies interpretation and, by examining spatial patterns, help to elucidate depositional dynamics. While following facies laterally is easy on the surfaces of recent sedimentary systems, detailed and, most of all, accurate maps of facies of larger study areas can only be derived from remote sensing data. To address this issue I have investigated the relationship between reefal facies groups on the Jebel Ali carbonate ramp, Dubai , U.A.E. A map of substrate distribution derived from high-resolution IKONOS satellite imagery has been combined with a bathymetric digital elevation model (DEM) to facilitate a fully three-dimensional model of the seafloor. Not only does this allow a detailed understanding of how topography and water depth influence facies distribution, but it is also evident that the spatial expression of facies patches display qualities that can be quantified using fractal concepts. The result is intriguing and will be the focus of future work that will focus on expanding the study to larger areas in different depositional settings.

3) Active remote sensing systems for seabed classification in reefal environments:
Although optical remote sensing delivers unparalleled results in shallow clear water, the limitations of the technology quickly become apparent when depth starts to exceed ~10 metres and/or water clarity is compromised by turbidity. Since large areas of important coral resources are situated outside the shallow areas of passive optical resolution, we are investigating active remote sensing technologies that are capable of resolving the seabed regardless of depth and water clarity. We have numerous projects using vessel-based acoustic systems (QTCView Series 5, Echoplus and RoxAnn) and are presently collaborating with John Brock of the USGS for the evaluation of the NASA Experimental Advanced Airborne Research Lidar (EAARL). Our results from the Arabian Gulf show that the acoustic systems can complement optical data sets despite the fact that classification is implemented on the basis of seabed rugosity as opposed to spectral diversity.

Selected Publications (Complete publication list)
Electronic copies of the papers below can be found here.

Myint S.W., Wentz L., Purkis S.J.. 2007. Employing Spatial Metrics in Urban Land-use/Land-cover Mapping: Comparing the Getis and Geary Indices. Photogrammetric Engineering & Remote Sensing. 73:1403-1415 AAG REMOTE SENSING SPECIALITY GROUP 2007 AWARD WINNER

Purkis, S.J., K.E. Kohler, B.M. Riegl, S.O. Rohmann. 2007. The Statistics of Natural Shapes in Modern Coral Reef Landscapes. Journal of Geology 115:493-508.

Papastamatiou, Y.P., S.J. Purkis, K.N. Holland. 2007. The response of gastric pH and motility to fasting and feeding in free swimming blacktip reef sharks, Carcharhinus melanopterus. Journal of Experimental Marine Biology and Ecology. 345:129–140.

Riegl, B.M., J. Halfar, S.J. Purkis, and L. Godinez-Orta. 2007. Sedimentary facies of the eastern Pacific’s northernmost reef-like setting (Cabo Pulmo, Mexico). Marine Geology 236:61-77.

Hernández-Cruz L.R., S.J. Purkis, B.M. Riegl (2006) Documenting decadal spatial changes in seagrass and Acropora palmata cover by aerial photography analysis in Vieques, Puerto Rico: 1937–2000. Bulletin of Marine Science. 79(2):401–414

Purkis, S.J., B.M Riegl, R.E. Dodge. 2006. Fractal patterns of coral communities: evidence from remote sensing. Proceedings of the 10th International Coral Reef Symposium, Okinawa, Japan. July 2004, p. 1753-1762.

Riegl, B.M., S.J. Purkis, K.E. Kohler, R.E. Dodge. 2006. Spatial patterns in Arabian Gulf coral assemblages (Jebel Ali, Dubai, U.A.E.) in response to temperature-forcing. Proceedings of the 10th International Coral Reef Symposium, Okinawa, Japan. July 2004, p. 683-687.

Purkis, S.J., S. Myint, B.M. Riegl. 2006. Enhanced detection of the coral Acropora cervicornis from satellite imagery using a textural operator. Remote Sensing of Environment. 101:82-94.

Riegl, B., R.P. Moyer, L.J. Morris, R.W. Virnstein, S.J. Purkis. 2005. Distribution and seasonal biomass of drift macroalgae in the Indian River Lagoon (Florida, USA) estimated with acoustic seafloor classification (QTCView, Echoplus). Journal of Experimental Marine Biology and Ecology 326:89-104.

Keck J., R.S. Houston, S.J. Purkis, B. Riegl. 2005. Unexpectedly high cover of Acropora cervicornis on offshore reefs in Roatán (Honduras). Coral Reefs 24:509.

Purkis, S.J.. 2005. A 'reef-up' approach to classifying coral habitats from IKONOS imagery. IEEE Transactions on Geoscience and Remote Sensing 43: 1375-1390.

Purkis, S.J., B. Riegl, S. Andréfouët. 2005. Remote sensing of geomorphology and facies patterns on a modern carbonate ramp (Arabian Gulf, Dubai, U.A.E.). Journal of Sedimentary Research 75:861-876.

Purkis, S.J. and B. Riegl. 2005. Spatial and temporal dynamics of Arabian Gulf coral assemblages quantified from remote-sensing and in situ monitoring data. Marine Ecology Progress Series 287:99-113.

Riegl, B. and S.J. Purkis. 2005. Detection of shallow subtidal corals from IKONOS satellite and QTC View (50, 200 kHz) single-beam sonar data (Arabian Gulf; Dubai, UAE). Remote Sensing of Environment 95:96-114.

Purkis, S.J. and J. Pasterkamp. 2004. Integrating in situ reef-top reflectance spectra with Landsat TM imagery to aid shallow-tropical benthic habitat mapping. Coral Reefs 23:5-20.

Purkis, S.J. .2004. Calibration of satellite images of reef environments. Ph.D. Thesis, Vrije Universiteit, Amsterdam, 205 pp. ISBN 90-9018043-5.

Purkis, S.J. and J.A.M. Kenter. 2003 ESF Consortium for Ocean Drilling (ECOD) White Paper - a summary of European accomplishments at the close of the Ocean Drilling Program (ODP). European Science Foundation ISBN 2-912049-39-3. 188pp.

Purkis, S.J., J.A.M. Kenter, E.K. Oikonomou, I.S. Robinson. 2002. High-resolution ground verification, cluster analysis and optical model of reef substrate coverage on Landsat TM imagery (Red Sea, Egypt). International Journal of Remote Sensing 23:1677-1698.