AusSeabed requires the L3 format to be supplied as GeoTIFFs, however the following formats can also be provided - a single resolution BAG, a variable resolution BAG and LAS/LAZ datafile (Table 10). A 3-band single-resolution GeoTIFF (depth, density, uncertainty) can be provided in addition to the independent single band definitions above and will be integrated into the AusSeabed Portal for simpler visualisation.
Polygons derived from L3 GeoTIFFs are also required to assist in updating the Master Data Holding Coverage. Converting L3 GeoTIFFs to shapefiles can be achieved using ArcGIS or GDAL (See ASB Procedures for Generating Polygons). The shapefile must represent the areal extent of the L3 product, which may not be the entire survey area.
Preferred Format | Specifications | |
Level | Bathymetry | |
L3 |
Priority 1 32-bit floating point GeoTIFF (.tiff)
BAG single-resolution
Priority 2 BAG multi-resolution, LAS/LAZ |
Bathymetry and Backscatter Vertical datums: Ellipsoid and MSL Resolution as per Table 3 Variable: coordinates, depth (m neg value) or intensity (dB), density (sounding/cell), uncertainty, flag (bathymetry in GeoTIFF format requires three separate files: depth, density, uncertainty Coordinate system: Geographic WGS84 or GDA2020 Precision: Metric variables with minimum of 2 decimals, Angular variables deg with 6 decimals Navigation and Ancillaries Date and Time: Calendar and UTC or specify otherwise. Coordinate system: Geographic WGS84 or GDA2020 with an ellipsoid height datum. |
Table 8. Preferred L3 formats.
BAG
The Bathymetric Attributed Grid (BAG) is a hydrographic exchange data format developed and maintained by the ONS-WG (Open Navigation Surface Working Group).
https://www.ngdc.noaa.gov/mgg/bathymetry/noshdb/ons_fsd.pdf
LAS
The LAS (LASer) format is a file format designed for the interchange and archiving of lidar point cloud data. It is an open, binary format specified by the American Society for Photogrammetry and Remote Sensing (ASPRS). (see OGC website for specification - https://www.ogc.org/standards/LAS
Algorithms
CUBE algorithm is highly recommended to produce bathymetry surface unless it is not possible/available. When generating bathymetric surfaces, seabed depths dictate the grid resolution. Grid resolution is determined by AusSeabed depth bands (Table 3). Typically, a single grid is made for a survey, but we also accept multiple grids. It is required that the bathymetry grid(s) extends from the start and end port of the survey (port to port).
Table 9. AusSeabed depth bands and associated grid resolutions. Modified from NOAA (2019)
Normal depth band (≤45°) | Steep slope depth band (>45°)1 | Res (m) | Ratio2 | ||||
Ds (m) | Dd (m) | Range Interval (m) | Ds (m) | Dd (m) | Range Interval (m) | ||
0 | 20 | 20 | 0 | 20 | 20 | 0.5 | 0.0250 |
18 | 40 | 22 | 16 | 40 | 24 | 1 | 0.0250 |
36 | 80 | 44 | 32 | 80 | 48 | 2 | 0.0250 |
72 | 160 | 88 | 64 | 160 | 96 | 4 | 0.0250 |
144 | 320 | 176 | 128 | 320 | 192 | 8 | 0.0250 |
288 | 640 | 352 | 256 | 640 | 384 | 16 | 0.0250 |
576 | 1280 | 704 | 512 | 1280 | 768 | 32 | 0.0250 |
1152 | 2560 | 1408 | 1024 | 2560 | 1536 | 64 | 0.0250 |
2304 | 5120 | 2816 | 2048 | 5120 | 3072 | 128 | 0.0250 |
4608 | 12000 | 7392 | 4096 | 12000 | 7904 | 210 | 0.01753 |
1In cases of steep slopes, the overlap between grids of different resolutions may need to be increased to prevent gaps in their junction. In these cases, the coarser resolution grid should have its shoaler extent modified to prevent this coverage gap. 2Highest resolution at which the dataset can support a minimum of five soundings per node (ideally, twice the maximum standard required survey resolution for the depth of the area, i.e. 2.5% water depth) (NOAA, 2019). 3Based on 1⁰ beamwidth (highest resolution that the current technology of shipborne systems can effort) because of the constraint in the minimum capture distance in CUBE to a maximum of 100.
[Source: https://australian-multibeam-guidelines.github.io/files/Australian-Multibeam-Guidelines-v2.0.pdf]
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