Processing

Data sources

Data required for creating L3 products are the L2 MBES (reduced to EGM2008) in proprietary format of the processing software used e.g. Caris HDCS_Data or in gsf format.

Processing steps

Steps for determining Grid Resolution (using Teledyne Caris)

Grid bathymetry according to the AusSeabed Depth Ranges Guide 2019 (Table 12) and apply associated AusSeabed CUBE parameters (Table 13). In configuration method, select browse button and select CUBEParams_AusSeabed_2019.xml and select appropriate configuration according to grid resolution e.g., Configuration = AusSeabed_0.5m (Figure 2). Utilise the AusSeabed CUBE parameters for optimised results.
Choose one grid for one survey area (do not subdivide) except when:
1. areas have large depth variations (e.g. from a continental shelf to an abyssal plane while transiting), and/or the resultant dataset will be split into multiple geotiffs and calculated for the best resolution for the area based on the geometry.
2. When gridding, break up at the end of the line if exceeding the boundary.
Every grid must not exceed depth variations more than 5 depth range intervals of the AusSeabed Depth Ranges Guide 2019 e.g., -20m to - 160m (Table 12).
For each grid, run first an auto-resolution grid in HIPS which will determine the best resolution for the chosen grid. Then round it to the nearest band in Table 12 and re-grid accordingly to this grid size.

Table 11. Simplified AusSeabed depth bands and associated grid resolutions.

Depth (m)	Resolution (m)
-20	0.5
-40	1
-80	2
-120	3
-160	4
-200	5
-240	6
-280	7
-320	8
-360	9
-400	10
-440	11
-480	12
-520	13
-560	14
-600	15
-640	16
-1280	32
-2560	64
-5120	128
-12000	210

Table 12. AusSeabed CUBE parameters[1].

Grid Resolution (m)	Minimum Capture Distance[2]	Capture Distance Scale (<=1%)[3]	Horizontal Error Scalar[4]
0.5	0.3535	0.5	1.96
1	0.707	0.5	1.96
2	1.414	0.5	1.96
3	2.121	0.5	1.96
4	2.828	0.5	1.96
5	3.535	0.5	1.96
6	4.242	0.5	1.96
7	4.949	0.5	1.96
8	5.656	0.5	1.96
9	6.363	0.5	1.96
10	7.07	0.5	1.96
11	7.777	0.5	1.96
12	8.484	0.5	1.96
13	9.191	0.5	1.96
14	9.898	0.5	1.96
15	10.605	0.5	1.96
16	11.312	0.5	1.96
32	22.624	0.5	1.96
64	45.248	0.5	1.96
128	90.496	0.5	1.96
210	148.47⁵	0.5	1.96

Figure 2. AusSeabed CUBE Parameters as a function of grid resolution as provided in the Australian Multibeam guidelines (https://australian-multibeam-guidelines.github.io/acquisition).

Decision tree for Processing

For some legacy data, CUBE cannot be performed, and Swath Angle is the preferred alternative. Decision tree is provided to help decide gridding algorithm.

Figure 3. Decision tree for gridding. *See dot points 3 and 4 in Section 6.2. ^Reduced to EGM2008, expecting L2 in EGM2008

[1] Based on NOAA’s, AHO’s HIPP and correspondences with Dr Calder.

[2] ²0.707xGrid_Resulution (NOAA, 2014; HIPP version 1.2).

[3] HIPP version 1.2 and NOAA (2014).

[4] CARIS automatically reset to 100, a maximum value allowed