Data Formats

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
D_s (m)	D_d (m)	Range Interval (m)	D_s (m)	D_d (m)	Range Interval (m)	Res (m)	Ratio²
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]