Processing

Data sources

Data required for further processing are L0 MBES (mandatory), L2 SVP (mandatory), L0 Navigation (e.g., Applanix POSMV) (optional), L2 Navigation (e.g., Applanix SBET & SRMS) (optional) and L2 tide (optional).

Processing steps

MBES Conversion – AusSeabed requires the processor to bring in ellipsoid height from the appropriate navigation channel (Figure 2) and to carry over raw data. The former enables ERS processing approach. The latter enables time series backscatter processing. Refer to the manual of the processing software used to meet these two requirements.

Optional Aux Conversion – This step is required only if L0 Navigation (e.g., Applanix POSMV) is available. It is highly recommended to import the following data:

Delayed Heave
Delayed Heave RMS
GPS Height
GPS Height RMS
Navigation
Navigation RMS
Roll RMS
Pitch RMS
Gyro RMS

The following step is only required if L2 Navigation (e.g., Applanix SBET & Applanix SRMS) is available. The following data are highly recommended:

GPS Height
GPS Height RMS
Navigation
Navigation RMS

Refer to the manual of the processing software used to meet these requirements.

Optional Tide Correction – This step only deals with data (usually legacy data) where ellipsoid height is not available (Figure 2). The tidal zone approach (e.g., Caris ZDF) reduced to EGM2008 is highly recommended. The entire MBES mapping area is divided into a subjective set of zones based on the size of the area. For each zone, a primary tide (either predicted or observed) is assigned. Two approaches to reduce to EGM2008 are: 1) all tides used are already in EGM2008 or, 2) in any vertical datum (either MSL or LAT) and appropriate offsets specified in ZDF. Refer to the manual of the processing software used and EGM2008 Approximation Methodology to meet this requirement.

Optional SVP Correction – This step is required when SVP artefacts are visible. Please reapply sound velocity profile to all L2 Survey data using the nearest distance method (within at least 6 hours). Refraction correction is not an alternative approach and is not recommended except where L2 SVP data isn’t available and data required correction for artefacts. Refer to the manual of the processing software used to perform this correction step.

Data Cleaning – Data must be cleaned from outliers and artefacts in the optimal resolution the data can support. There is no standard procedure as to how to achieve this requirement. This can be achieved by automated (surface cleaning) and additional manual cleaning processes as required.

L2 Export – Fully processed L2 data must be exported to gsf format. It is a blackbox operation. Almost all software currently available do not allow users to specify what to export, except adopting their software-specific predefined settings. The only option available for the user to choose is whether or not to include time series backscatter. As such, we have noticed some variations in gsf files between Caris-derived and QIMERA-derived gsf; for example,, while Caris exports ellipsoid height (or GPS height) available in their proprietary format to gsf, QIMERA does not.

Figure 2. Decision tree for choosing appropriate EGM2008 vertical datum approach. See EGM2008 Approximation Methodology.