INS Filter Aiding Sources

The INS filter in Subsonus can accept position and velocity aiding from multiple sources. These filter aiding sources can be configured in the web UI - see Filter Aiding

GNSS Compass

A GNSS Compass is most commonly used to provide a vessel mounted Subsonus unit with absolute position, velocity and heading. When using the Advanced Navigation GNSS Compass as an aiding source it will typically initialise within 5 minutes. Detailed information about the satellite constellations, fix type and system health can be viewed in the web UI of the GNSS Compass.

Acoustic Positioning

The USBL hydrophone array in Subsonus resolves angles and distances underwater. Typically a pair of Subsonus units are operated together in bi-directional acoustic communication to resolve relative positioning between the two devices and transfer navigation data.

A Subsonus configured as a slave device is positioned with respect to a master unit that also has access to an absolute world coordinate system reference such as GNSS or a fixed location. The USBL and acoustic modem functions of Subsonus can then transfer the absolute position data from the master Subsonus to the slave Subsonus.

A Subsonus will start acoustic positioning within 10 seconds of the hydrophone array being submerged underwater and acoustic contact with another Subsonus unit being established.

Acoustic Heading

A unique feature of Subsonus is its ability to transfer heading data acoustically. The bi-directional measurement and communication between two Subsonus units equipped with USBL hydrophone arrays allows the known heading of a vessel mounted surface Subsonus unit to be transferred to a subsea Subsonus unit. The integrity of this acoustic heading data is significantly better than magnetic heading sensors which are prone to disturbance from nearby metal objects.

The acoustic heading feature is enabled and active by default.

Pressure Depth

Subsonus contains a pressure depth sensor that can measure up to 100 bar. The sensor can provide both position and velocity aiding to the navigation filter. To use the position aiding capability the pressure sensor offset must be set before submerging Subsonus. This offset can be set on the filter aiding configuration page “Configuration”→”Filter Aiding”, see Filter Aiding.

Magnetic Heading

Subsonus contains a magnetic heading sensor which can be used when a more accurate aiding source such as GNSS or acoustic heading is unavailable. The magnetic heading features automatic calibration that occurs continuously when a second heading source is available. In the event that the Subsonus unit is going to be mounted in the presence of a strong magnetic interference source (such as close to a motor or high current wiring) then the magnetic heading should be disabled. This can be done on the filter aiding configuration page. If magnetic heading is disabled Subsonus will maintain heading using its gyroscopes is conditions where acoustic heading is unavailable.

Internal GNSS

The Subsonus contains an internal GNSS receiver and antenna mounted in the top of the hydrophone array. If the Subsonus is out of the water with the hydrophone array facing the sky the system will typically acquire a 3D GNSS fix within 30 seconds. This will be displayed as an aiding source on the “view”→”status” page. The internal GNSS receiver can be disabled on the filter aiding page. See Filter Aiding.

When Subsonus is taken below the water level the GNSS positioning will stop since the GNSS satellite signals cannot penetrate water. The USBL acoustic positioning will take over at this point. When the unit breaches the water surface again the acoustic positioning will cease and Subsonus will automatically start using the internal GNSS positioning again.

External Data Sources

Subsonus can be configured to use external aiding data from other instruments such as external velocity from a DVL. Please contact support@advancednavigation.com for further information about using external data aiding with Subsonus.