Importing Bathymetric Datasets
Multiple Bathymetric Datasets
Limited bay bathymetry
- NOAA – Offshore datasets
- LIDAR – Shoreline and nearshore (important for structure resolution)
- Channel
NJ State maintains north channel and north bay channel
Federally maintained entrance and south channel (15 years)
- NAN-supported field data collection
Included bathymetry of the backbay (Spring High Tide)
Common Spatial Reference Datum & Vertical Datum
Tides and Currents (NOAA)
https://tidesandcurrents.noaa.gov/
Vertical Datum Conversions
Prep for the Coastal Modeling System
- Based off of a Cartesian grid
- Planar coordinate system
- Model computation is in metric and depths are positive from zero (elevations are flipped)
- Grid is generated based off of a single bathymetry file stored in SMS scatterset file format
- Vertical datum is not specified and is assumed local
- The boundary condition forcing (tidal) must be in the same datum as the bathymetry
- Typically modeling grids are brought to a mean datum such as mean sea level (msl) or mean tide level (mtl)
- This requires that all datasets are brought in to unified projection, datum, and units
- Shark River Inlet bathymetry will be converted to State Plane horizontal coordinates in meters with the vertical datum set to MSL in meters
Reprojecting Coordinates and Changing Datums
Object Projection tells SMS what the coordinates are to be project in. This can modify the location that SMS will display the dataset. Checking “Specify” Project Projection is how coordinates are converted to a different projection and vertical datum.
Converting Elevations to Depths (CMS Requirement)
Data Transform Can adjust scatterset data by scaling, translating (adding/subtracting), or rotating horizontal or veritcal
Select Depths Elevations Flips negative elevations to positive depths. Necessary for CMS model calculation.
NAN Channel Surveys
- Horizontal Datum:
State Plane NAD27 New Jersey 2900 (ft)
- Vertical Datum:
MLW (ft) – COE Datum (not local NOAA benchmark)
Conversions
NAN Channel Surveys Extended in to Bay
- Horizontal Datum:
State Plane NAD27 New Jersey 2900 (ft)
- Vertical Datum:
MLW (ft) – COE Datum (not local NOAA benchmark)
Dataset Calculator
NJ DEP Channel Surveys
- XYZ pulled out of drawing and changed to ascii format
Provided conversion from local datum to NAVD88: MLW à NAVD88 + 2.41 ft (0.735 m) MLW à MSL + 2.17 ft (0.661 m)
Field Data Collection – Multibeam Bay Bathymetry (August 2009)
Horizontal Datum: State Plane NAD83 New Jersey 2900 (m) Vertical Datum: NAVD88 (m)
LIDAR
- Files are emailed in separate sections from the NOAA CSC Archive
- Typically several to 10s of files that are 5 - 100 mb in size
- Compiling takes time
- Points have been sampled/filtered and cropped to area of interest
- Horizontal Datum:
State Plane NAD83 New Jersey 2900 (ft) Vertical Datum: NAVD88 (ft)
Coastal Relief Model (DTM/DEM)
- Generate a 3 sec (pt/3rd second) grid
Coastal Relief Model
- Horizontal Datum:
Geographic NAD83
- Vertical Datum:
MSL (m) – Not accurate for shallow bathymetry (used for offshore)
Extra Bathymetry
- Convert shoreline shapefile in SMS
- Horizontal Datum:
State Plane NAD83 New Jersey 2900 (ft)
- Added extra bay contour (set to -0.75 m)
Convert a Shapefile to Map
- Drag and drop the shapefile (.shp)
- Highlight all Coastline Mapping – Shapes and Feature Objects
- Turn off GIS Data Arcs generated where GIS polylines
Convert a Map to Scatter
- Highlight all Arcs, Rt-Click Redistribute Vertices Specified Spacing (spacing in spatial coordinates)
- Feature Objects Map à Scatter Include all feature points and vertices (vertices spacing was set to 10)
- Modify as necessary (i.e. remove entrance channel shoreline because it is old seawall and jetty configuration – LIDAR used here)
Create a Contour Polyline in the Map Module
Select Default Coverage under Map Data
- Type à Generic à Mapping/Observation/Shoals
- Draw arcs (polylines) feature with tool
- Select arcs and convert the z elevation to the desired contour elevation
Create Scatterset Points from Map Data
- Select arcs to redistribute the spacing of vertices Feature Objects à Redistribute Vertices Specify Spacing based on horizontal coordinate system units (metric in this case)
- Feature Objects à Map>Scatter Include Feature Pts and vertices and the Arc Elevations
All Files Referenced to Same Horizontal and Vertical Datum
- Delete unnecessary data points (check alignment and elevations in overlapping datasets)
Merging Scattersets
- Merging all scattersets will integrate all points. Overlapping areas of scattersets should either be deleted, or use a separate method of merging (by prioritizing using triangles).
Surface-water Modeling System (SMS)
Questions?
Tanya Beck Tanya.m.beck@usace.army.mil
Or
Mitch Brown Mitchell.e.brown@usace.army.mil