Acoustic Ground Discrimination Systems (AGDS)

Fast mapping of sublittoral habitats without Fast mapping of sublittoral habitats without limitations due to turbiditylimitations due to turbidity

based on the Procedural Guidelinebased on the Procedural Guideline

1-3 of the “Marine Monitoring Handbook”1-3 of the “Marine Monitoring Handbook”

What can AGDS discriminate?

different types of sediments (e.g. clay, sand, different types of sediments (e.g. clay, sand, pebbles, rock)pebbles, rock)

biological structures (e.g. seagrass, biological structures (e.g. seagrass, macroalage, mussel beds)macroalage, mussel beds)

Why should we use an AGDS in Environmental Impact

Assessments? produce a habitat map toproduce a habitat map to

find a suitable site for a mariculture facilityfind a suitable site for a mariculture facility identify rare and fragile habitatsidentify rare and fragile habitats identify already disturbed areasidentify already disturbed areas

produce a topographic map which is a prerequisite for produce a topographic map which is a prerequisite for many models and the selection of sampling stationsmany models and the selection of sampling stations quickly estimate community parameters, guidance for quickly estimate community parameters, guidance for

selecting sampling stationsselecting sampling stations get a baseline for future monitoringget a baseline for future monitoring

What Do We Need?

Two skilled and experienced persons & helmsmannTwo skilled and experienced persons & helmsmann A vessel with a stable working platform and preferably a A vessel with a stable working platform and preferably a

dry cabindry cabin An echo-sounder (typically single beam)An echo-sounder (typically single beam) An AGDS signal processor (RoxAnn, QTC, etc.)An AGDS signal processor (RoxAnn, QTC, etc.) Computer System with data logging/visualizing softwareComputer System with data logging/visualizing software (Differential) GPS(Differential) GPS Power SupplyPower Supply Equipment for Ground Truthing …Equipment for Ground Truthing …

Survey DesignAGDS Coverage

AGDS Coverage - Recommendations from the

“Marine Monitoring Handbook”

concentrate effort on problematic areasconcentrate effort on problematic areas track spacing should be related to along-track track spacing should be related to along-track

variability (real-time visualization necessary!)variability (real-time visualization necessary!) track spacing wider than 500 m is problematictrack spacing wider than 500 m is problematic Tracks should extend beyond the main area of interestTracks should extend beyond the main area of interest Shoreline should be tracked as far inshore as possible Shoreline should be tracked as far inshore as possible

(operational depth of ship and AGDS)(operational depth of ship and AGDS)

Ground TruthingMethod

Drop-down video (preferred)Drop-down video (preferred) Towed video systemsTowed video systems GrabsGrabs Side scan sonarSide scan sonar SCUBA Diving, practicable only for small SCUBA Diving, practicable only for small

areas (frequent up and downs are risky!)areas (frequent up and downs are risky!)

Ground TruthingStations

cover full range of acoustic ground types cover full range of acoustic ground types (E1/E2-space, Q-space)(E1/E2-space, Q-space)

cover full geographic rangecover full geographic range at least 5 stations per classat least 5 stations per class focus on problematic habitatsfocus on problematic habitats locate stations locate stations onon homogenous tracks homogenous tracks

Data Analysis

Filtering and exploration: spreadsheet, Filtering and exploration: spreadsheet, databasedatabase

Interpolation: e.g. SurferInterpolation: e.g. SurferTMTM, , VerticalMapperVerticalMapperTMTM

Classification: image processing software Classification: image processing software like ERDAS Imaginelike ERDAS ImagineTMTM and Irdist and IrdistTMTM

Spatial analysis and map production: GIS-Spatial analysis and map production: GIS-SoftwareSoftware

Quality Assurance 1. Survey

Make sure that visualized data are plausibleMake sure that visualized data are plausible Make sure data are consistent in cross-tracks and close Make sure data are consistent in cross-tracks and close

parallel tracks, track over a patch of homogenous ground at parallel tracks, track over a patch of homogenous ground at the start and finish of the daythe start and finish of the day

Avoid acoustic interference with other echo-soundersAvoid acoustic interference with other echo-sounders air bubbles under the transducer cause erratic depth recordsair bubbles under the transducer cause erratic depth records Avoid slow vessel speed (less than 1 mph) and rapid Avoid slow vessel speed (less than 1 mph) and rapid

changes in directionchanges in direction Keep accurate field log: equipment details, geodetic Keep accurate field log: equipment details, geodetic

parameters, change of settings, disturbances, sea parameters, change of settings, disturbances, sea conditions, … conditions, …

Quality Assurance2. Data

Consistency between habitat maps and Consistency between habitat maps and ground samples used for classificationground samples used for classification

Consistency between habitat maps and Consistency between habitat maps and independent ground samplesindependent ground samples

Relationship between survey intensity and Relationship between survey intensity and performanceperformance

Consistency between different AGDS data Consistency between different AGDS data sets for the same sitesets for the same site

Costs