ONC currently deploys two different types of hydrophone arrays: the Tetrahedron Array and the Box Array. The individual hydrophones are mounted in different positions as outlined in the sections below.

Hydrophone Array Positions

Hydrophones in an array are mounted in designated positions that are labeled as A, B, C, or D. This naming convention is used for both the older tetrahedron array design and the new box array design, however the exact A, B, C, D positions differ slightly in each array design, which is outlined further below.

The A, B, C, or D positions can be found on the hydrophone's attributes page when searching with it's device ID. This URL can be assembled such as: https://data.oceannetworks.ca/DeviceAttributesService?deviceId=50320 where 50320 is an example of a hydrophone device ID. The position attribute code is named "HydrophoneArrayPosition" and the value is listed as "deviceAttributeValue". In this example case it would be A.

Tetrahedron Array

• B and D would always be on the same side as the bullhorns (the bullhorns with the cable wrapped around them, if there is more than one side with bullhorns)
• B would be on the right, D would be on the left, as you look at the platform from that side

For the older JASCO ECHO/ULS hydrophone platforms, this used a slightly different naming convention which used labels 1, 2, 3, and 4 instead of A, B, C, and D, and the positions between C/D and 3/4 were swapped.

Box Array

• A is always directly above C in this setup

Heading

The local North direction is taken as the perpendicular to the line between B and D, in the direction of A/C.

Note that the heading is recorded by an ROV in Degrees True North as opposed to Degrees Magnetic North. See below section on how to find this value on the Oceans 3.0 site.

Hydrophone Array Coordinates

The coordinates refer to the x, y, and z distance from the origin point to each hydrophone positions A, B, C, and D. For both array designs, the point of the x, y, z origin is directly beneath A on the seafloor. For the HydrophoneArrayCoordinates attribute, this is expressed as a string of comma separated numbers "x,y,z" where x, y, and z are in meters from the origin to the hydrophone position.

Similar to the array positions, the coordinates can be found on the hydrophone's attributes page when searching with it's device ID. This URL can be assembled such as: https://data.oceannetworks.ca/DeviceAttributesService?deviceId=50320 where 50320 is an example of a hydrophone device ID. The position attribute code is named "HydrophoneArrayCoordinates" and the value is listed as "deviceAttributeValue". In this example case it would be 0,0,2.175.

For both array designs:

• The X-axis is parallel to the line between B and D
• The Y-axis is perpendicular to the X-axis in line with A/C
• The Z-axis is the vertical distance from seafloor (up is positive)

Below is an example for how the coordinates are determined from engineering diagrams for a Box Array

The left diagram shows the array in the XY plane (ie. top down view) where the x and y values can be determined.

• Hydrophones A and C are at the point of origin in this plane, so they both have X=0 and Y=0.
• Hydrophone B has an x value of -0.70m and a y value of +0.71m
• Hydrophone D has an x value of +0.70m and a y value of +0.71m

The right diagram shows the array in the XZ plane (ie. front view) where the z values can be determined (Note: the diagram shows dY but our conventions use height as the z-axis)

• Hydrophone A has a z value of +2.175m (total of both distances from seafloor)
• Hydrophones B, C, and D have a z value of +1.175m

Therefore the HydrophoneArrayCoordinates are determined to be the following

An example of a deployed hydrophone array:

How to find position and heading information in Oceans 3.0

Once you have selected a hydrophone device from the Data Search page, you can navigate to its Device Listing page for detailed metadata information by clicking the Details link in the highlighted window

From the opened Device Listing page, you can navigate to the Site tab to find additional site metadata.

Under the Site tab, you can find a list of all the previous sites the hydrophone has been deployed to, including when the hydrophone was recovered back to the Marine Technology Center. By selecting a Site you can find more detailed information such as the site's latitude and longitude coordinates, depth, and heading. More specific details on the heading including how it is recorded can be found in the above section.