Mission Modes

Multiple mission modes are available. Each includes Mission Settings and Mission Tasks.

The workflow is slightly different for each.

Mission Mode	Configured from web UI	Controlled from web UI
GNSS / Dead Reckoning	Hydrus: Plan Mission	Hydrus: Run
Subsonus Assisted	Hydrus: Plan Mission	Subsonus: Deployment
Spot Inspection	Subsonus: Deployment	Subsonus: Deployment
Hull Inspection	Subsonus: Deployment	Subsonus: Deployment
Tank Inspection	Hydrus: Run Mission	Hydrus: Run
Pool Inspection	Hydrus: Run Mission	Hydrus: Run

Subsonus Assisted Mission Mode

This mission mode requires a Subsonus USBL. Missions are deployed and tracked from within the Subsonus web interface, which communicates directly with the Hydrus.

The integration of the Hydrus and Subsonus systems enables accurate positioning and mid-water vehicle tracking, even in the presence of varied bottom currents. By utilising the Subsonus acoustic positioning capabilities, a precise location of Hydrus can be determined and monitored in real-time. This ensures that Hydrus stays on track during missions. In case of prolonged acoustic communication outage, Hydrus will autonomously enter dead reckoning navigation mode and navigate independently.

From the Subsonus web interface, you can initiate acoustic communication with the Hydrus. Acoustic communication is used for transmitting mission instructions, receiving status updates, and making any necessary adjustments to the course or operations of the Hydrus.

GNSS / Dead Reckoning Mission Mode

This mission mode allows for missions to be carried out with a standalone Hydrus unit, and is configured and initiated from the Hydrus web UI.

In GNSS / Dead Reckoning mission mode, without the aid of a Subsonus, Hydrus will acquire a GNSS fix at the surface, and then carry out the mission based on dead reckoning navigation, with the autopilot relying on the sensor data from the INS and DVL. At regular intervals throughout the mission, or when accuracy is deemed poor, the unit will resurface in order to acquire a GNSS fix. This will give Hydrus an exact position reference and will enable the system to make any navigation adjustments if required.

Within the Mission Planner, access “Menu → Edit Advanced Settings… → Behaviour" to show:

Current mission’s mode
Travel Tilt
Transit Vertical
If “Transit at Surface” is selected, Hydrus will travel at the water surface when performing transit sections of the mission.

Upon completion of the mission, Hydrus will return to the planned recovery location and automatically surface at that location. Once at the surface, it will utilise its thrusters to stay directly above the recovery location based on its current GNSS position. In case Hydrus is tipped upside down while at the surface, it will dive down, correct its orientation and then resurface again.

GNSS / Dead Reckoning missions are:

Suitable for shallow waters and locations that are difficult or impossible to reach with a boat equipped with Subsonus.
Suitable for mission depths up to 30 metres. Deeper missions are possible, however, the deeper the mission in standalone mode, the more drift prone the accuracy is. If available, consider Subsonus assisted mission mode for deeper missions.
Suitable when launching missions from shore, a jetty, small boat.
Not recommended in open water scenarios with large swell or choppy conditions.

Note that at the end of a mission, Hydrus will go straight to the surface in the specified recovery location. Consequently, it is important that the area around the retrieval point is clear of overhead obstacles, for example a jetty or a boat.

Spot Inspection

Spot Inspection is a mission task designed for quickly inspecting a small, specific area of interest in the vertical plane. This task is executed via Manual Control . With this mode engaged, Hydrus will dive to a pre-set depth, orient its camera horizontally with a heading in the forwards direction, and then rotate on the spot to capture video and images of the target. This is ideal for rapid assessments of underwater assets or points of interest without the need to define a complex survey pattern.

Tank Inspection

Tank Inspection is a standalone mission mode optimized for enclosed, GNSS-denied environments where surface tracking is infeasible.

It is configured and initiated from the Hydrus web interface without requiring a Subsonus transceiver array. It is recommended to be run in conjunction with a tether to facilitate retrieval. Tracing accounts for a tether and adjusts to minimize tether entanglement.

This mode requires purchasing an additional firmware license to unlock the Hull Inspection functionality.

Hull Inspection

Hull Inspection mode is used to track a pattern under the hull of a vessel, and is typically set up next to a ship at dock. It requires pairing with a Subsonus which is typically mounted on the neighboring wharf. It is initiated and controlled from the Subsonus web interface.

The Hydrus calculates absolute and relative position from the hull using distance from the Subsonus when in line-of-sight to the Subsonus, and additionally uses dead-reckoning with DVL and inertial sensors when on the far side of the hull.

This mode requires purchasing an additional firmware license to unlock the Hull Inspection functionality.

Pool Inspection Mission Mode

The Pool Inspection mission mode is used when using the Hydrus in a swimming pool without a GNSS position solution.

In this mode the Hydrus will initialise the position at the location of the first waypoint with the Hydrus using dead reckoning navigation for the remainder of the test.