Combining optical and acoustic data to enhance the detection of Caribbean forereef habitats

Maps of coral reef habitats are fundamental tools for reef management, and high map accuracy is desirable to support appropriate decisions, such as the stratification of marine reserves by habitat class. While satelite sensors have been used to map different reef communities, the accuracy of these maps tends to be low (overall accuracy<50%) and optical airborne methods with high spectral resolution have, to date, been the most effective (if expensive) means of achieving higher accuracy. A potential means of compensating for the low spectral and radiometric resolution of optical satellite data, which is a major cause of its poor performance, is to combine satellite data with acoustic remote sensing. This study quantified the benefit of the synergy between optical satellite data (IKONOS) and acoustic (RoxAnn) sensors. The addition of acoustic data provided three new data axes for discriminating habitats: seabed roughness (E1), reef depth (z) and the depth correction of satellite spectral data to uniform depth. Seabed hardness (E2) was not an informative channel in our study. The use of z to conduct the water-column correction of the optical bands to uniform depth is a potential improvement over applying the depth-invariant index approach to optical data in the absence of ancillary information on depth. Habitat maps of the forereef of Glovers Atoll (Belize, Central America) were created using k-means unsupervised classification on eleven different treatment images constructed from various combinations of optical and acoustic data layers. The maximum benefit of data synergy was achieved by depth correcting the optical bands. The accuracy of maps based on the depth-invariant optical index was not enhanced when E1, E2 or z were added as separate layers but was enhanced when these three acoustic measures were added in concert. Data synergy can improve the accuracy of habitat maps and the availability of both data sets allows practitioners to take advantage of each techniques' additional strengths such as providing synoptic continuous imagery for education and general management planning (in the case of optical imagery) and maps of reef rugosity (in the case of acoustic data). (C) 2010 Elsevier Inc. All rights reserved.

[1]  Zhenkui Ma,et al.  Tau coefficients for accuracy assessment of classification of remote sensing data , 1995 .

[2]  Serge Andréfouët,et al.  Coral reef habitat mapping using remote sensing: A user vs producer perspective. implications for research, management and capacity building , 2008 .

[3]  Chris D. Clark,et al.  Coral reef habitat mapping: how much detail can remote sensing provide? , 1997 .

[4]  R. Steneck,et al.  Coral Reefs Under Rapid Climate Change and Ocean Acidification , 2007, Science.

[5]  D. Rundquist,et al.  Classifying and Mapping General Coral-Reef Structure Using Ikonos Data , 2002 .

[6]  C. Menza,et al.  Predictive mapping of fish species richness across shallow-water seascapes in the Caribbean , 2007 .

[7]  G. De’ath,et al.  Establishing Representative No‐Take Areas in the Great Barrier Reef: Large‐Scale Implementation of Theory on Marine Protected Areas , 2005 .

[8]  Sarah L. Benfield,et al.  Mapping the distribution of coral reefs and associated sublittoral habitats in Pacific Panama: a comparison of optical satellite sensors and classification methodologies , 2007 .

[9]  P. Mumby,et al.  Benefits of water column correction and contextual editing for mapping coral reefs , 1998 .

[10]  Samuel J. Purkis,et al.  Detection of shallow subtidal corals from IKONOS satellite and QTC View (50, 200 kHz) single-beam sonar data (Arabian Gulf; Dubai, UAE) , 2005 .

[11]  Mapping seabed biotopes at two spatial scales in the eastern English Channel. Part 2. Comparison of two acoustic ground discrimination systems , 2004, Journal of the Marine Biological Association of the United Kingdom.

[12]  John R. Jensen,et al.  Introductory Digital Image Processing: A Remote Sensing Perspective , 1986 .

[13]  P. Mumby,et al.  A review of remote sensing for the assessment and management of tropical coastal resources , 1996 .

[14]  R. Pasterkamp,et al.  Integrating in situ reef-top reflectance spectra with Landsat TM imagery to aid shallow-tropical benthic habitat mapping , 2004, Coral Reefs.

[15]  Peter J Mumby,et al.  Biological and remote sensing perspectives of pigmentation in coral reef organisms. , 2002, Advances in marine biology.

[16]  N. Frazer,et al.  Multi-spectral mapping of reef bathymetry and coral cover; Kailua Bay, Hawaii , 2003, Coral Reefs.

[17]  P. Mumby,et al.  Development of a systematic classification scheme of marine habitats to facilitate regional management and mapping of Caribbean coral reefs , 1999 .

[18]  Chris D. Clark,et al.  Spectrographic imaging: A bird's-eye view of the health of coral reefs , 2001, Nature.

[19]  C. Folke,et al.  Ecological goods and services of coral reef ecosystems , 1999 .

[20]  S. Andréfouët,et al.  Change detection in coral reef communities using Ikonos satellite sensor imagery and historic aerial photographs , 2003 .

[21]  P. Dustan,et al.  Landsat Thematic Mapper: Detection of Shifts in Community Composition of Coral Reefs , 2001 .

[22]  S. Purkis,et al.  Distribution and seasonal biomass of drift macroalgae in the Indian River Lagoon (Florida, USA) estimated with acoustic seafloor classification (QTCView, Echoplus) , 2005 .

[23]  S. Andréfouët,et al.  A comparison of Landsat ETM+, SPOT HRV, Ikonos, ASTER, and airborne MASTER data for coral reef habitat mapping in South Pacific islands , 2003 .

[24]  Peter J. Wright,et al.  An assessment of the acoustic survey technique, RoxAnn, as a means of mapping seabed habitat , 1997 .

[25]  R. Stumpf,et al.  Determination of water depth with high‐resolution satellite imagery over variable bottom types , 2003 .

[26]  Ian Sotheran,et al.  Mapping marine benthic biotopes using acoustic ground discrimination systems , 2003 .

[27]  Samuel J. Purkis,et al.  Spatial and temporal dynamics of Arabian Gulf coral assemblages quantified from remote-sensing and in situ monitoring data , 2005 .

[28]  S. McNeill.  The selection and design of marine protected areas: Australia as a case study , 1994, Biodiversity & Conservation.

[29]  J. L. Pérez-Lloréns,et al.  Single-beam acoustic ground discrimination of shallow water habitats: 50 kHz or 200 kHz frequency survey? , 2008 .

[30]  J. Bythell,et al.  Habitat mapping in the Caribbean for management and conservation: Use and assessment of aerial photography , 1995 .

[31]  B. Deronde,et al.  Mapping of coral reefs using hyperspectral CASI data; a case study: Fordata, Tanimbar, Indonesia , 2008 .

[32]  Peter J. Mumby,et al.  Remote sensing of the coastal zone: An overview and priorities for future research , 2003 .

[33]  Peter J. Mumby,et al.  Mapping marine environments with IKONOS imagery: enhanced spatial resolution can deliver greater thematic accuracy , 2002 .

[34]  D. Neil,et al.  An evaluation of Landsat Thematic Mapper (TM) digital data for discriminating coral reef zonation: Heron Reef (GBR) , 1994 .

[35]  André Morel,et al.  Diffuse reflectance of oceanic shallow waters: influence of water depth and bottom albedo , 1994 .

[36]  P. Mumby,et al.  Remote Sensing Handbook for Tropical Coastal Management , 2000 .

[37]  Erik Næsset,et al.  Conditional tau coefficient for assessment of producer's accuracy of classified remotely sensed data , 1996 .

[38]  P. Mumby,et al.  Digital analysis of multispectral airborne imagery of coral reefs , 1998, Coral Reefs.

[39]  J. Jaubert,et al.  The cover of living and dead corals from airborne remote sensing , 2004, Coral Reefs.

[40]  Coral reef habitat , 1982 .

[41]  V. Quintino,et al.  Sea-bottom classification across a shallow-water bar channel and near-shore shelf, using single-beam acoustics , 2005 .

[42]  Fred J. Tanis,et al.  Multispectral bathymetry using a simple physically based algorithm , 2006, IEEE Transactions on Geoscience and Remote Sensing.

[43]  Peter J Mumby,et al.  Modeling the beta diversity of coral reefs. , 2006, Ecology.

[44]  M. P. Lesser,et al.  Bathymetry, water optical properties, and benthic classification of coral reefs using hyperspectral remote sensing imagery , 2007, Coral Reefs.

[45]  V. Quintino,et al.  Acoustic seabed classification of marine habitats: studies in the western coastal-shelf area of Portugal , 2003 .

[46]  Katherine A. Call,et al.  Coral reef habitat discrimination using multivariate spectral analysis and satellite remote sensing , 2003 .

[47]  Samuel J. Purkis,et al.  A "Reef-Up" approach to classifying coral habitats from IKONOS imagery , 2005, IEEE Transactions on Geoscience and Remote Sensing.

[48]  G. Gilat,et al.  Method for smooth approximation of data , 1977 .

[49]  Alastair R. Harborne,et al.  Using an Acoustic Ground Discrimination System to map coral reef benthic classes , 2003 .

[50]  J. Veron,et al.  Corals of the world , 2000 .

[51]  V. Quintino,et al.  Benthic biotopes remote sensing using acoustics , 2003 .

[52]  S. Thrush,et al.  Detection of acoustic class boundaries in soft sediment systems using the seafloor acoustic discrimination system QTC VIEW , 2001 .

[53]  Anders Knudby,et al.  Assessing the effect of management zonation on live coral cover using multi-date IKONOS satellite imagery , 2007 .

[54]  C. Wayne Wright,et al.  LIDAR optical rugosity of coral reefs in Biscayne National Park, Florida , 2004, Coral Reefs.

[55]  S. Andréfouët,et al.  Choosing the appropriate spatial resolution for monitoring coral bleaching events using remote sensing , 2002, Coral Reefs.

[56]  D. Lyzenga.  Passive remote sensing techniques for mapping water depth and bottom features. , 1978, Applied optics.

[57]  E. LeDrew,et al.  The scientific issues surrounding remote detection of submerged coral ecosystems , 1998 .

[58]  Stuart R. Phinn,et al.  Multi-site evaluation of IKONOS data for classification of tropical coral reef environments , 2003 .