Waterline Height

The Waterline Height component defines long-period changes in the vessel draft due to fuel burn or other loading changes. Specifically, it defines the height of the waterline below the Reference Point (RP).

If you want the waterline height to be applied during the Georeference Bathymetry process, you must enter it here. If the waterline height is not entered here, HIPS uses a default of zero as the height.

No interpolation of waterline height is done during sound velocity correction.

The Waterline Height component has the following attributes in the Attributes window:

• Date: The year and Julian day of the current waterline time stamp (see Component Time Stamps).

• Time: The hour and minute of the current waterline time stamp (see Component Time Stamps).

• Waterline: The vertical distance from the waterline to the RP. This is positive when the waterline is below the RP.

For Kongsberg data, Waterline must be set to the same value recorded as WLZ in the Kongsberg Installation Datagram.

• Apply: Select Yes to apply Waterline to the processed depths during Georeference Bathymetry (see the table below for details).

The Waterline attribute is used during the Georeference Bathymetry process as described in the table below. The table uses the following terms:

• “Observed depths” describe soundings relative to the position of the sonar. These depths can be either raw depths that were derived from the range and angle information and had just a basic refraction correction applied, or they can be refined depths that have undergone full sound velocity correction during acquisition or in HIPS and SIPS.

• “Processed depths” describe soundings that have been fully corrected and stored in a global coordinate system. They are the result of georeferencing the observed depths using the position and orientation system of the vessel.

HIPS SVC Enabled in Vessel File	SVC in Current Run of Georeference Bathymetry	Previous Runs of Georeference Bathymetry	Apply in Waterline Height	Behaviour of Georeference Bathymetry
True	Enabled	Any	Any	Georeference Bathymetry uses Waterline to position the sonar head in the sound velocity profile (SVP). It also applies Waterline to the observed depths. Georeference Bathymetry does not directly apply Waterline to the processed depths, but the corrections from Waterline are carried over when it georeferences the observed depths into processed depths.
True	Disabled	Georeference Bathymetry was previously run with SVC enabled.	Any	Georeference Bathymetry detects that SVC was already performed on the data, so it does not apply Waterline to the observed depths and processed depths.
False	Disabled	Georeference Bathymetry was never previously run with SVC enabled.	True	Georeference Bathymetry does not apply Waterline to the observed depths but does apply it to the processed depths. If your sonar applies its own waterline value to the observed depths during acquisition, then the processed data will incorrectly have two waterlines applied to it. See the note below for details.
False	Disabled		False	Georeference Bathymetry does not apply Waterline to the observed depths and processed depths.

Some sonar systems (such as Kongsberg) apply their own waterline value to their observed depths during acquisition. The Georeference Bathymetry process can either keep the sonar’s waterline value or apply the Waterline value set in the Waterline Height component of the vessel file. As of version 12 of HIPS and SIPS, this is controlled by the vessel’s HIPS SVC Enabled property (see Vessel).

If the vessel’s HIPS SVC Enabled property is set to True and you run Georeference Bathymetry with SVC enabled, then it will recreate the observed depths while applying the Waterline value from the vessel file’s Waterline Height component instead. Note that in this case Georeference Bathymetry applies the Waterline value even if its Apply attribute is set to False.

If HIPS SVC Enabled is set to False, Georeference Bathymetry uses the observed depths that were directly imported from the sonar (which already include the sonar’s own waterline value). Note that it is possible to accidentally apply both the sonar’s and the vessel file’s waterline values if all of the following are true:

• The vessel file has HIPS SVC Enabled set to False, and;

• The vessel file’s Waterline Height component has Apply set to True, and;

• Georeference Bathymetry has never been previously run on the dataset with SVC enabled, and;

• Georeference Bathymetry is run on the dataset with SVC disabled.

In such a case, Georeference Bathymetry will keep the sonar’s waterline value in the observed depths and also add the vessel file’s Waterline value to the processed depths, resulting in incorrect data. To avoid this, set Apply to False in the Waterline Height component of the vessel file.

The HIPS SVC Enabled property is read-only. When you create a new vessel file, the New Vessel Wizard asks you to specify whether to enable HIPS SVC. When you upgrade a vessel file created with an earlier version of HIPS and SIPS, HIPS SVC Enabled is set to True if the existing vessel file was set up for SVC. In both cases, HIPS SVC Enabled cannot be changed later.