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Indian River Lagoon Seagrass Mapping
Keith Patterson, PSM, SP, GISPSenior Project ManagerGeospatial and Technology ServicesDewberry [email protected]
TOPICS
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• Importance
• Methods
• Results
• Trends
WHY MAP SEAGRASS?
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Seagrass, a submerged flowering plant found in shallow waters, provides food,habitat, and nursery areas for numerous vertebrate and invertebrate species.
Seagrass communities are sensitive to changes in water quality.
The distribution and extent of seagrass is considered a barometer of the healthestuarine systems.
The Indian River Lagoon is considered as oneof the most biodiverse lagoonal ecosystemsin the Northern hemisphere and is home tomore than 3,000 species of plants andanimals.
PROJECT AREA – INDIAN RIVER LAGOON
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The Indian River Lagoon is agrouping of three lagoons onthe Atlantic Coast of Floridathat include the MosquitoLagoon, Banana River, andthe Indian River.
AERIAL PHOTOGRAPHY ACQUISITION
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Digital Imagery Acquisition
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Aircraft: Cessna 206Sensor: Microsoft UltraCamX (or
similar camera) – very high resolution, large format digital camera
• Typical Imagery Acquisition Platform
Imagery Acquisition Flight Plan
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Flight lines are planned according to the area of interest
• 12 inch Ground Sample Distance (GSD)
• 4- Band Imagery
• Stereo Collection
Optimal Imagery Requires Pre-flight Planning along with Daily Condition Monitoring
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Pre-flight Scheduling• Weather, wind• Biomass (April – June)• Sun angle below 30 degrees (glare)
Pre-flight Water Condition Monitoring• Turbidity• Tidal influence• Water releases• Rain events• Wave height (glint)
Dewberry has a network of information providers to help with condition monitoring so that conditions are evaluated prior to flying.
Limited collection window each day
May/June: start of thunderstorm season
When to Fly?
9 | Indian River Lagoon Seagrass MappingFlight Plan Sun Angles WeatherTides
Indian River North Lagoon 2011 Algae Bloom
Complicated Time-Sensitive Acquisition
Biomass
Algae Bloom
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SEAGRASS
Imagery
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Quality control is then performed to ensure the visibility of submerged features:
• Review flight logs (sun angles)• Compare new imagery to known
seagrass locations • Evaluate water clarity throughout
the project area• Conduct re-flights if necessary
Aerial imagery is acquired:• April - May • Every two years
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GEOREFERENCING THE AERIAL PHOTOGRAPHY
Aerial Triangulation (AT)
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PURPOSE: Removes distortion from the imagery and accomplishes georeferencing to the Earth
Inputs to the aerial triangulation solution:Airborne GPS/IMU data captured during flight records GPS position / pitch, roll, yaw (heading) of the aircraft
Photo-identifiable ground control points are collected via ground surveying and are used to improve the aerial triangulation result.
Sensor calibration information specific to the geometric properties of the camera is considered within the AT solution.
QUALITY CONTROLSpatial Accuracy Assessment
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PURPOSE: Spatial accuracy is tested before mapping begins.
• Otherwise: False changes in seagrass extent could be mapped
• Surveyed “Check Points”
• Photo-identifiable features appearing on imagery are surveyed. The check points are then compared with the georeferenced imagery.
IMAGERY DELIVERABLES
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ORTHOPHOTOGRAPHY
• Used primarily as a backdrop on laptops in the field and within ArcGIS during ancillary data comparison
STEREO IMAGERY
• Used for photo interpretation within photogrammetric workstations
FIELD WORK
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Field Work
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Purpose:
Imagery Signature Identification• Ties imagery signatures (colors, tones, texture) to
seagrass occurrence in the field • Performed during the imagery acquisition phase
Groundtruthing• Resolves photo interpretation questions and
facilitates quality control• Performed during photo interpretation
Thematic Accuracy Assessment• Tests classification accuracy• Performed after final mapping• Over 200 accuracy assessment points are used
Field Work
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PROCESS:• Field points are mostly pre-selected while in the office
• The photo interpreters travel to and locate each pre-selected field point accurately via GPS.
• The seagrass at the field location is compared to the imagery and ongoing mapping using snorkeling and underwater video
• Seagrass classification and extent is documented while in the field using ArcMap.
• A Photointerpretation Key (i.e. mapping guide) is produced for use during photointerpretation so that seagrass is mapped consistently.
Field Equipment
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Field Work
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Fieldwork using watercraft, snorkeling, underwater video, GPS and GIS
INDIAN RIVER LAGOON SEAGRASS
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PHOTO INTERPRETATION
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Photo Interpretation - Change Analysis
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Performed using stereo photogrammetric workstations
• Prior linework compared to new imagery and edited for seagrass changes
• Ancillary data is continually accessed• Field data • Bathymetry• Historical imagery• Satellite imagery
• Image histograms are adjusted for maximum visualization
• Mapped data is stored within ArcGIS
• Field visits are conducted during the photo interpretation phase to check habitat changes
Inputs to Decision Making – Is it a valid change?
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SEAGRASS CHANGE IDENTIFIED
REVIEW 2013 IMAGERY
SIGNATURE
REVIEW 2013 LINEWORK
REVIEW ANCILLARY
GEOSPATIAL DATA AND FIELD DATA
REVIEW 2015 IMAGERY
SIGNATURE
SEAGRASS CHANGE DIGITIZED
CONSULT PI KEY
VISIT FIELD IF
NECESSARY
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CLASSIFICATION CODES
5400 Unvegetated Bottom <10% cover
9113 Seagrass, Patchy
9116 Seagrass, Continuous ≥10% cover
Continuous seagrass polygons are further classified according to the percent cover of seagrass (i.e. density) existing within each polygon. 100%, 80%, 60%, 40%, 20%
NO SAV Not Classified (land, islands, mangroves, etc.)
Edge Confidence Classification:
HC High Confidence
MC Moderate Confidence
LC Lower Confidence
Photo Interpretation Editing Process
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The 2013 seagrass map is updated (digitally edited) to reflect 2015 conditions:
• Ensures that only true seagrass changes are recorded within the data
• Ensures that un-changed seagrass beds remain un-changed in the data
• Allows for the generation of change maps using GIS
• Change statistics can be summarized for the project
Blue linework = 2011Purple linework = 2013
MOST IMPORTANT: The methods yield reliable maps and statistics that quantify the amount of seagrass change over time.
Mapped Seagrass Examples
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Continuous Seagrass (9116)Patchy Seagrass (9113)Unvegetated Bottom (5400)
MONITORING TRANSECTS
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FIELD TRANSECTS ARE MONITORED UNDER A DIFFERENT PROGRAM
• Visited yearly during the summer since 1994• Document the species, depth, density of
seagrass• Data from the transects can be used to
validate the mapping on a site-specific basis
TYPICAL MONITORING TRANSECT
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Special Thanks To:LAUREN HALL, St. Johns River Water Management District - Environmental Scientist who diligently documents these transects each year and provides significant support to the seagrass mapping effort as well.
Unfortunately, the news is not good
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CHANGE STATISTICS
TREND ANALYSIS
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2015 ACREAGE = 58,792
2007 ACREAGE = 80,442
1992 ACREAGE = 65,032
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CONTINUED MAPPING/MONITORING IS NEEDED
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THANK YOU!
Keith Patterson, PSM, SP, GISPSenior Project ManagerGeospatial and Technology ServicesDewberry [email protected]