About transducer geometry

Transducer geometry in Echoview refers to the configurable location and orientation of transducers. This page covers:

For information about how transducer geometry affects displayed data and exports, see What is affected by transducer geometry.

Overview of transducer geometry

Each transducer may be located in space and oriented as desired. Illustrated below is a schematic displaying the relative positions in space of a reference point, a GPS antenna and a transducer with non-vertical orientation. How to define location and orientation for each transducer is described below.

Platform system reference point

Transducers are always associated with a platform. The system reference point of the platform is at (0,0,0) by definition and defines the position of the platform in the real world (that is, the platform is considered to be, in the real world, wherever it's reference point is). The position of the system reference point may be specified so that the system reference point is mapped with respect to the WGS84 datum. Transducer location and orientation and the Z coordinate of the water level are entered relative to the system reference point.

For many applications, such as a typical ship based echo integration survey with multiple downward looking transducers, the only aspect of transducer geometry required is the definition of transducer depth (draft), if desired. Other applications, such as multiple frequency TS techniques, surveys with non-vertical transducers, and applications that require the position of samples to be precisely located in the world, Echoview's transducer geometry settings allow full specification of the transducer set up.

Echoview transducer geometry settings allow enough information to be stored about the location and orientation of transducers and platform X-Y position of the GPS antenna to determine the geographic coordinates of any sample or single target in the acoustic beam - given the assumption of a stable platform with no pitch and no roll.

Pitch and roll

Echoview may be able to read pitch and roll from some data file formats or from text files (check the details for your format). Roll may be corrected for in Echoview, but this is not applied to the platform. It is applied to variables directly and makes specific limiting assumptions. Pitch may be corrected for in Echoview, but this is not applied to the platform. It is applied to variables directly and makes specific limiting assumptions. For further information regarding relevant data formats and the effects of using roll and pitch data see About roll data, About pitch data.

Heave

Echoview can apply heave compensation via a Heave source. The application of heave assumes that the motion sensor data represents the movement of the platform system reference point. In effect, the usage of heave data assumes the sensor and transducer experience that same motion. For further information regarding relevant data formats and the effects of using heave data see About heave compensation.

Notes:

About transducer location

The relative location of the water level and GPS antenna are defined on the Position page of the Platform Properties dialog box.

The location and orientation of each transducer is defined on the Transducer Properties dialog box. A platform may support more than one transducer.

Locations are all defined relative to a system reference point. The coordinate system utilizes three axes (X, Y and Z) and their orientation depends upon whether the platform is fixed or mobile.

Fixed Platform

The platform system reference point (0, 0, 0) is in a platform space where:

The geographic location for the platform system reference point is to a specified latitude, longitude and altitude. Positive altitude is upwards.

Mobile Platform

The platform system reference point (0, 0, 0) is in a platform space where:

The geographic location for the platform system reference point (X = 0, Y = 0) is the latitude and longitude of the GPS antenna as measured by a Global Positioning System (GPS) device. The location of the GPS antenna relative to the system reference point is specified in X, Y coordinates in meters. The altitude of the system reference point (Z = 0) may be specified. Positive altitude is upwards.

To determine the geographic location of a sample point or a single target in geographic coordinates it is also necessary to define the orientation of the transducer. 

About transducer orientation

Transducers are not only located, but also oriented - that is, they point somewhere. Like location, orientation requires three parameters to be specified, in this case angles rather than coordinates. The orientation for each transducer is defined on the Orientation page of the Transducer Properties dialog box.

The X-Y-Z axes as defined above are taken as a reference for orientation. In summary:

For fixed platforms:

  • The X axis runs south-north

  • The Y axis runs west-east

  • The Z axis runs up-down

For mobile platforms:

  • The X axis runs stern-bow

  • The Y axis runs port-starboard

  • The Z axis runs up-down

Two angles are used to define the direction in which the acoustic axis is pointing (either elevation and azimuth angles or alongship and athwartship angles). A third angle called the rotation defines the direction of the minor axis of the transducer relative to a vertical plane passing through the beam axis. The rotation of the transducer can only be determined after the definition of the beam direction.

Elevation and Azimuth

The angles are defined as follows:

defines a vertically downward pointing beam

90°

a horizontal beam

180°

a vertically upward pointing beam

defines a northward (or forward) pointing beam

90°

eastward (or starboard) pointing

180°

southward (or aft) pointing

270°

westward (or port) pointing

If the elevation is 0° or 180° then Azimuth is equivalent to a rotation.

Along- and Athwartship (Mobile Platform only)

The angles are defined as follows:

defines a downward pointing beam in the Y-Z plane

-90°

a horizontal aft pointing beam

90°

a horizontal forward pointing beam

-180°

an upward pointing beam in the Y-Z plane

180°

an upward pointing beam in the Y-Z plane

defines a downward pointing beam in the X-Z plane

-90°

a horizontal port pointing beam

90°

degrees a horizontal starboard pointing beam

-180°

an upward pointing beam in the X-Z plane

180°

an upward pointing beam in the X-Z plane

Note: Not all combinations of Alongship and Athwartship angle are valid. If one angle defines a downward pointing beam (-90° to 90°) and the other an upward pointing beam (-180° to -90°or 90°to 180°)  they cannot be describing the same direction!

Rotation

Valid range is 0° to 360°.

an upward pointing positive minor-axis

180°

a downward pointing positive minor-axis

In Summary

To determine the three coordinates defining the beam orientation do the following:

  1. Determine the pointing direction of the beam axis.

    Use your choice of either elevation-azimuth angles or alongship-athwartship angles.
     

  2. Determine the rotation angle of the transducer.

    Remember that the zero reference for the rotation angle is the vertical plane running through the beam axis and therefore that the rotation coordinate can only be meaningfully determined after you have defined the orientation of the beam axis.

Examples:

Notes:

See also

About echograms
EV File Properties, Echogram page

Transducer Properties dialog box

About draft

Logged draft warning

Depth, Range and Altitude

About beam geometry

What is affected by transducer geometry?
About heave compensation
Transducer geometry illustrated - fixed platform