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Evaluation of a new hydroacoustic substrate
classification system for oyster reef mapping
in Galveston Bay, Texas
2003-2014
Introduction
Importance of Oyster Reef Resources
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Vital in maintaining the Galveston Bay ecosystem.
Provide habitat for bottom-dwelling fish and
invertebrates which attract larger game fish.
Stabilize the bay bottom and break wave energy,
preventing shoreline erosion.
Oysters act as a natural filtration system; they filter
silt and contaminants from the water.
Support an important commercial fishery.
Photo – Jennifer Reynolds, The Daily News
2003-2014
Introduction
Researchers at Texas Parks and
Wildlife Department (TPWD)
have worked for years to quantify
and map oyster reefs.
Utilize a variety of technology
including side-scan sonar &
scientific echosounder and
various data processing methods.
Photo – TPWD
Vital in guiding restoration and
management efforts. Important
in establishing a baseline for
future surveys and developing an
index for monitoring temporal
changes.
2003-2014
Introduction
TPWD evaluated a new hydroacoustic processing
software (BioSonics Visual Habitat) for the rapid
assessment and mapping of various substrate
types (sand, cobble, mud, etc.)
2003-2014
Methods – Data Collection
Echosounder Configuration
• 120 kHz, 7.6 0 single beam transducer
• Ping rate: 5 pps
• Pulse duration: 0.4 ms
• Calibrated, scientifically defensible
• Quantitative assessment
• All data stored in DT4 file format
2003-2014
Methods – Study Area
Hanna’s Reef, Galveston Bay, TX
5.7 sq km rectangular grid of 10 transects
spaced 200 m apart.
2003-2014
Methods – Study Area
Hanna’s Reef, Galveston Bay, TX
5.7 sq km rectangular grid of 10 transects
spaced 200 m apart.
2003-2014
Methods – Data Processing
All data were derived from the same DT4 files and processed to
generate 5 substrate classes.
Hydroacoustic data were processed using three different
software programs/methods:
1.
(new program)
2.
QTC Echo Impact
3.
TPWD proprietary SAS method
Results plotted over side-scan sonar imagery and survey data in
ArcGIS (V. 10.2)
2003-2014
Different software methods resulted in similar substrate classes
but assigned to different class/cluster numbers.
For ease of interpretation, similar substrates were given matching
colors among methods during mapping in ArcGIS.
Method:
Visual Habitat
(Color Code / Substrate)
QTC Impact
(Color Code/Substrate)
TPWD-SAS
(Color Code/Substrate)
1
Orange/Mud1
Light Green/Shell
Dark Green/Mud Shell
2
Red/Mud 2
Dark Green/Mud Shell
Light Green/Shell
3
Light Green/Shell
Orange/Mud1
Yellow/Reef
4
Dark Green/Mud Shell
Red/Mud 2
Orange/Mud1
5
Yellow/Reef
Yellow/Reef
Red/Mud 2
Acoustic Habitat
Class/Cluster No.
2003-2014
Methods – Data Processing
1.
- principal components analysis
2.
QTC Echo Impact – PCA, 166 variables
3.
TPWD proprietary statistical analysis software
(SAS) method – combines output from VBT2
(Beta) with factor analysis (PROC Factor) and K
means cluster analysis (PROC Fastclus) in SAS.
2003-2014
Methods – Data Processing
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Evolution of BioSonics VBT/VBT2 software based on
work of M. Moszynski of Gadansk Univ. of Tech. and
J. Tegowski of the Univ. of Gadansk.
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Unsupervised classification approach
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Generates 14 “features” (variables)
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Principal Components Analysis (PCA) of features
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Results output to ArcGIS for mapping over side scan
imagery and historical survey data, or export direct
to KML format for viewing sharing via Google Earth
2003-2014
Methods – Data Processing
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PCA result displayed as
scatterplot
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Users choose the
number of clusters
(classes) to form
2003-2014
Methods – Data Processing
QTC Impact:
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Unsupervised classification approach
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Generates 166 “features” (variables)
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PCA of Features
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Required adjustment of “BioSonics Base Gain” value in
program’s configuration file (impact.cfg) prior to analysis
(which was very time consuming).
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No longer commercially available!
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Results output to ArcGIS for mapping over side scan imagery
and historical survey data.
2003-2014
Methods – Data Processing
TPWD Proprietary Statistical Analysis
Software (SAS) method:
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Supervised Classification Approach
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Used 51 Variables generated by BioSonics VBT2 (Beta).
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In SAS, factor analysis (PROC Factor) used to assess the
number of classes (e.g., clusters) needed to account for
≥75% of variance.
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K Means Cluster Analysis (PROC Fastclus) used to bin
pings into clusters.
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Results output to ArcGIS for mapping over side scan
imagery and historical survey data.
2003-2014
Side Scan Sonar
A Portion of Hanna’s Reef and Vicinity
Side Scan Mosaic
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Benthos C3D bathymetric
side scan sonar
Oyster habitat (and other
hard substrates) indicated
by darker areas
Oyster Reef
2003-2014
Prior Survey Data
Powell et al., (1993)
Acoustic Survey
• Dual frequency Datasonics
DFT-210 echosounder
• Towed transducers
operating at 27 and 200 kHz
• Paper chart recorder
• Acoustic technique
described by Simmons et al.
(1992)
• Three bottom types were
defined/identified via
groundtruthing
• ARC/Info used to map reef
areas
2003-2014
Methods – Defining Substrate Types
Similar results from all 3 methods:
Legend:
Two classes clearly associated with oyster habitat
(Reef and Shell). Reef habitats are best left alone.
Shell habitats good candidates for restoration.
Class
1. Shell
2. Reef/shell
Remaining 3 classes are sedimentary.
3. Mud - dredge dug
One sedimentary class (Mud Shell) appears to be a
mud/shell mix or transitional class. This is the least
abundant of the 5 classes and thus is the most
difficult to sample precisely.
2003-2014
4. Mud
5. Reef
Merging Data Layers
A Portion of Hanna’s Reef and Vicinity
Hydroacoustic Data Processed using BioSonics Visual Habitat
Legend:
Visual Habitat
1. Shell
2. Reef/shell
3. Mud dredge dug
4. Mud
5. Reef
Powell et Al 1993
Mud
Reef
Shell
2003-2014
Merging Data Layers
A Portion of Hanna’s Reef and Vicinity
Hydroacoustic Data Processed using QTC Impact
Legend:
QTC Impact
1. Shell
2. Reef/shell
3. Mud dredge dug
4. Mud
5. Reef
Powell et Al 1993
Mud
Reef
Shell
2003-2014
Merging Data Layers
A Portion of Hanna’s Reef and Vicinity
Hydroacoustic Data Processed using TPWD Proprietary Method
Legend:
TPWD
1. Shell
2. Reef/shell
3. Mud dredge dug
4. Mud
5. Reef
Powell et Al 1993
Mud
Reef
Shell
2003-2014
Merging Data Layers
Visual Habitat
QTC impact
TPWD
2003-2014
Results
Results with Visual Habitat very favorable compared to both TPWD’s method
and QTC Impact (the "gold standard" IMHO) for classifying reef and shell
habitats.
In non-reef areas, QTC Impact results tended to be more homogenous.
Visual Habitat and TPWD’s method gave more heterogeneous results in nonreef areas. Is this a more accurate representation of small scale habitat
patchiness? More precise ground truthing needed.
If identifying oyster habitat is the only concern, fewer classes might be
better. Visual Habitat performed quite well using a 4-class analysis,
especially over the shell habitats.
While all 3 methods performed well at classifying oyster habitat, BioSonics
Visual Habitat was the least time consuming method and significantly
reduced level of effort as compared to QTC and TPWD SAS method.
2003-2014
Results - 4 Classes w/Visual Habitat
A Portion of Hanna’s Reef and Vicinity
Hydroacoustic Data Processed using BioSonics Visual Habitat
Legend:
Visual Habitat
1. Shell
2. Mud dredge dug
Visual Habitat performed
quite well using a 4-class
analysis, especially over the
shell habitats.
3. Mud
4. Reef
Powell et Al 1993
Mud
Reef
Shell
2003-2014
Results
In Galveston Bay habitat types are patchily distributed at small spatial scales,
especially in non-reef areas.
Visual Habitat showed a high agreement with prior results and resulted in a
significant reduction in effort as compared to processing with other
software.
In addition to the significant reduction in effort, Visual Habitat provided data
visualization tools in the form of a transect map view displaying user-defined
color gradients for each data layer.
Visual Habitat also provides the ability to export results in KML file format
for rapid interpretation via Google Earth as well as the ability to export as
csv for easy import into other applications (e.g., AutoCAD and ArcGIS).
2003-2014
Evaluation of a new hydroacoustic substrate
classification system for oyster reef mapping
in Galveston Bay, Texas
Thank you for your time.
Questions:
Bill Rodney
bill.rodney@tpwd.texas.gov
281-534-0127
Eric Munday
eric@subsea2020.com
855-SUBSEA1
2003-2014