11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 17: Emerging Techniques in Remote Sensing and Geospatial Analysis
17-5
Calibration And Validation Of Coral Reef Benthic Community Maps From High-
Spatial Resolution Satellite
Chris ROELFSEMA* 1 , Stuart PHINN 2
1 Centre for Remote Sensing and Spatial Information Science, University of Queensland,
St.lucia, Australia, 2 Centre for Remote Sensing and Spatial Information Science,
University of Queensland, St.Lucia, Australia
Our ability to map coral reef environments using remote sensing has increased, through
availability of suitable images, field methods and software. Appropriately developed and
validated maps are essential for management agencies to decide if they will use these data
for science and management decisions. The objective of this paper is to present a simple
approach for calibrating and validating maps of coral reef benthic communities derived
from high-spatial resolution satellite images. Two forms of field data for calibration and
validation were applied in a supervised classification of high spatial resolution Quickbird
image data to map coral reef benthic communities. Data were acquired in 2006 for three
Fijian reefs representing areas with variable water clarity and benthic cover composition.
The two types of field data were benthic cover estimates derived from: (1) photo transects
and (2) spot checks. Each of the two field data sets were used separately with the satellite
imagery to digitise two sets of polygons around target benthic community types. These
polygons were used as training sites for two supervised image classifications, producing
two maps of benthic community classes for each site, based on transects and point data
respectively. An independent subset of the polygons was used as reference data for
accuracy assessment. For the three sites mapped, no differences in overall map accuracy
were observed between the two types of benthic community maps: 66 % for transect and
65% for spot check based maps. However, the transect based calibration polygons were
considered to be more representative of the benthic cover due to the number of sample
points and their spatial distribution. This approach showed that standard digital camera
and GPS, can provide adequate field calibration and validation data for mapping coral
reef communities from high spatial resolution satellite imagery for a ranges of
environments.
17-6
Spatial Prediction Of Reef Bathymetry And Geomorphology Using High-Resolution
Satellite Imagery
Joaquin R GARZA-PEREZ* 1 , Eugene C RANKEY 2 , Robert N GINSBURG 2,3 , Stacy L
REEDER 4,5 , Sean A GUIDRY 6 , Humberto GUARIN 7
1 UMDI-Sisal, Fac. de Ciencias, UNAM, Sisal, Mexico, 2 MGG, RSMAS, U. Miami,
Miami, FL, 3 Ocean Research and Education Foundation, Coral Gables, 4 MGG, RSMAS,
U. Miami, Miami, Mexico, 5 Schlumberger-Doll Research, Cambridge, 6 ExxonMobil
Development Company, Houston, TX, 7 Bert Instruments, Inc., Hollywood, FL
In general, geomorphology and depth are the basic drivers behind many physical and
biotic processes on reefs and coastal environments. These factors shape hydrodynamics
and gradients of environmental factors as water energy, light absorption and temperature,
therefore the distribution of organisms varies accordingly. To better understand the
morphology of reef systems, we generated 3-D models of bathymetry by applying
generalized regression analysis and spatial prediction (GRASP) models based on highresolution
(2.4 -5 m resolution) satellite imagery. This technique utilizes the spatial
structure of the sea bottom in imagery to generate accurate geomorphology models and
bathymetry maps. The innovation of this methodology is the virtual independence of the
differences in bottom albedo to generate a predictive map of depth. The technique has
been successfully implemented in different Caribbean reef environments. The resulting
grids/rasters and 3-D surfaces are used as a basis for static and dynamic modeling and
spatial predictions of reef habitat distribution, biodiversity hotspots, reef condition, fish
biomass and abundance, sediment transport, and hydrodynamics and connectivity.
17-7
Casi Mapping Of The Farasan Islands (Saudi Arabia): Ecosystem Processes in An
Atypical Red Sea Setting
Gwilym ROWLANDS* 1 , Sam PURKIS 1 , Bernhard RIEGL 1 , Philip RENAUD 2
1 National Coral Reef Institute (NCRI), Nova Southeastern University, Dania, FL, 2 Khaled bin
Sultan Living Oceans Foundation, Landover, MD
The Red Sea is typified by expansive fringing-reefs affixed to a narrow and steep coastal shelf.
We present work from the South of the Red Sea where a rather different geomorphology exists.
The little studied marine system of the Farasans consists of vast shallow sediment-rich banks
rising from deep water, a morphology that profoundly affects the depositional environment.
Satellite imagery and 3,000 km2 of airborne CASI imagery were acquired over this remote
seascape. Hydrodynamic measurements atop the banks revealed low flushing rates and
temperatures notably higher than encountered in adjacent deep water. These stressful factors
appear to render the setting sub-optimal for corals. The hyperspectral CASI data coupled with
exhaustive field survey allowed mapping of benthic character across the Farasan archipelago at
exceptionally fine spatial resolution. In addition, bathymetry was retrieved from a spectral
derivation of the CASI data, trained using numerous acoustic soundings made during the field
campaign. The investigation reveals an abundance of fine-grained sediment sheets on-lapping
topographic highs dominated by algal meadows. Despite the unfavourable environmental
conditions, expansive areas of live coral were also found. These were concentrated either within
shallow micro-atoll fields in the bank interior, or in deeper habitats within large but diffuse
‘coral fields’ interspersed with high algal cover. Though the region does not lack suitable
substrate and is locally rich in coral, little evidence for frame-building was observed. The
mapping revealed that the location of coral-dominated habitat was not random, but rather
clustered in the northern (upstream) sector of the archipelago. Corals were not found to favour a
particular depth regime, but the axis of orientation for these areas was consistent between
banks. The study highlights an unusual coral setting in the Red Sea and successfully proves the
existence of a vibrant but atypical ecosystem.
17-8
An Investigation of Seagrass Patterns at Alphonse Atoll, Seychelles: Linking Structure To
Function In Marine Landscapes
Sarah HAMYLTON* 1 , Tom SPENCER 1
1 Department of Geography, Cambridge Coastal Research Unit, Cambridge, United Kingdom
The idea of landscapes as shifting patch mosaics, structured by a range of biological and physical
stochastic forces, is well suited to shallow tropical environments, where seagrass patches lie within a
matrix of soft sediments or rocky substrates. The interaction of wave fields and tidal currents with reef
growth, carbonate sediment transport, erosion and accretion can result in linear morphologies, such as
shore-normal spur and groove, striation of reef flat material and alternating sand tongues and seagrass
beds. Patch-level metrics capture phenomena such as linearity in one variable, which can be evaluated
over a gradient of predictable environmental change. A shift in focus, from the properties of the
individual patch to the statistical properties of ensembles, enables the links between observed structures
and the processes that govern them to be empirically investigated, yet studies of shallow benthic
communities at this scale have tended to be restricted to qualitative descriptions only.
Remote sensing technology provides the opportunity to investigate critical controls of landscape
mosaics through the application of geostatistical techniques to patch assemblages. Alphonse Atoll in
the Seychelles was mapped using an aircraft-mounted, high resolution (1 m 2 pixel), multispectral (17
band) Compact Airborne Spectrographic Imager (CASI). Subsequent image processing and
classification procedures generated habitat maps composed of vector data structures that represent reef
features as discrete units, analogous to the concept of patches conventionally adopted by
landscape ecologists. Combining habitat maps with georeferenced attribute data yields spatial data
matrices that can be manipulated in a GIS environment to develop models that simplify natural
processes by linking structure to function on coral reefs. This study demonstrates how remotely sensed
habitat maps can be used to generate quantitative spatial variability models based on the geography of
the data, a key property of remotely sensed imagery.
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