How-to Monitor Seabed Collision Avoidance

Seabed Collision Avoidance Monitoring is intended to warn if there will be a collision with the seabed / terrain ahead within a certain time.

E.g. for a deeptow towfish, based on current towfish 3D position, speed over ground and course over ground the function tests to see if there will be a collision with the selected seabed model within the entered time.
When the seabed is at the same depth or shallower than the current towfish depth and within the maximum time, then an alarm is generated in different displays (navigation, profile, generic and alert).

Any node can be selected for this, it doesn't have to be a deeptow towfish.
The seabed model can be the current sounding grid, an additional terrain or a user defined sounding grid.

Page contents:

Online

Controller

In the Controller go to Session Setup - Monitoring.

• Select 'Seabed Collision Avoidance' as Type.
  • (Read the How-to Monitor Dynamic Moon Pool Area for the 'Dynamic Moon Pool Area' Type.)
• Select the object and the node for which you want to know if it will collide.
• Set the Maximum Time (e.g. when the Maximum Time is set to 45 minutes and the expected time to collision is more than 45 minutes, no alarm will be shown).
• Select the Seabed Model Source.
  • Three different seabed model sources can be used:
    • Storage Grid (as specified in Session Setup - Storage - Sounding Grid)
    • Additional Terrain (as specified in Session Setup - Planning - Additional Terrains)
    • User Defined Grid (browse for an existing grid)

Tip

Storage Grid can be used e.g. when there is a multibeam system in front of the node that is used for the seabed collision monitoring (e.g. the multibeam can be at the front of the vessel and a side scan sonar fish is towed behind the vessel).

Tip

The 'Seabed Model Source' that is selected needs to contain a layer of the 'Bathymetry' type.
The algorithm will use the following search order:

1. Maximum height (= shallowest depth) attribute
2. Mean height attribute
3. Value attribute

Navigation Display

No additional settings need to be made in the Navigation Display.

No Alert

When there is no alert, a dashed green line will be shown in the Navigation Display which represents the Maximum Time calculated based on COG and SOG.

Alarm

When there will be a collision within the Maximum Time, the collision point will be shown, together with distance and time until collision.

Profile Display

In the Profile Display Seabed Collision should be enabled.
This can be done under View Properties - Monitors.

No Alert

When there is no alert, the Profile Display will show nothing extra.

Alarm

When there will be a collision within the Maximum Time, a red line and the collision point will be shown, together with distance and time until collision.

Alert Display

In the Alert Display an alert should be created of the Category Computation Result and the Type Monitor.

No Alert

When there is no alert, the status is OK and the Collision-Monitor alert is green.

Alarm

When there will be a collision within the Maximum Time, the status will change to Alarm and the Collision-Monitor alert is red.

Generic Display

Under Result Data - Monitoring, all the Monitoring related items can be selected.
See the online Help file 'Monitoring' in which all the items are explained.

No Alert

When there is no alert, the Collision Status is OK and shown in green.

Alarm

Info

The Collision Status can also be 'Warning' or 'Error'.

A 'Warning' status may be generated when:

1. No sounding grid information is available for some of the sample points along the vector which is traveled with the Maximum Time.

An 'Error' status may be generated when:

1. No position was found for the selected node. 
2. An invalid position was found for the selected node.
3. The computed sample interval is equal to or less than zero.
4. More than 100000 sample positions would be needed. This may be prevented by decreasing the 'Maximum Time' field.