Accuracy and limitations
- AusSeabed
Some MBES and Navigation & Attitude acquisition systems may be incompatible with these specifications and alternative products could still be derived from such data. Acceptance of the data into the AusSeabed DataHub, in this case, would be conditional. The position of all navigational aids shall be determined such that the horizontal and vertical uncertainty meets IHO-2 standard or better (HIPP SOR, 2022).
Care should be taken in areas of rapidly changing depth where the sound velocity profile (SVP) is significantly different in deeper and shallower waters. In such areas, additional SVP may need to be collected. At a minimum, SVPs must be measured at 12-hourly intervals with SV accuracy of better than 0.5 m/s and depth of +/-0.01 m. The SVP should also be configured in ‘smart mode’ such that sound speed is recorded at fixed depth increments (e.g., 0.5m).
A minimum of 35 day observations is required for a single predicted or measured tide time series.
Patch tests determine the misalignment relative to the motion sensor and gyro as well as the time offset to the GPS system. Because misalignment erodes accuracy, it is essential to conduct a patch test prior to data acquisition. This is valid for all multibeam systems permanently mounted, routinely calibrated or installed on a vessel of opportunity.
Systems must be recalibrated following any alteration to the components of a survey system as it may cause a misalignment.
The patch test is essential as it confirms timing and alignment of the MBES sensor, vessel and IMU reference frames. The results of the patch test should be reported in the Mobilisation and Calibration Report. The results must be applied in the acquisition system prior to MBES data acquisition. It is essential that the patch test is conducted according to Refer to Australian Multibeam guidelines 2020 v2.0.
The accuracy of the Navigation and Attitude data vary from sensor to sensor and are available from their respective fact sheets. Teledyne Caris provides summary of all known sensors in their website (https://www.teledynecaris.com/en/products/total-propagated-uncertainty/ ).
© Commonwealth of Australia (Geoscience Australia) year of publication.
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