Multibeam analysis variables

Multibeam data can be analyzed via 3D objects. The following types of 3D object analysis variables are available:

3D_region metrics
3D region integration analysis variables

Surface metrics

3D region track metrics

Multibeam target detection properties are automatically exported with single targets data.

3D region metrics

These variables can be viewed on the General page of the (3D Object) Properties dialog box.

The following variables are output when you export 3D regions analysis.

Variable

Unit

Description

Region_class_name

-

Name of the class the 3D region belongs to.

Region_name

-

Name of the 3D region.

Region_id

-

Identification number of the 3D region.

Vertices

-

Number of vertices in the 3D region. This includes the vertices of any vacuoles in the 3D region.

Triangles

-

Number of triangles in the 3D region. This includes the triangles of any vacuoles in the 3D region.

Surface_area

m2

Surface area of the 3D region. This includes the surface area of any vacuoles in the 3D region.

Length_NS

m

Maximum length of the 3D region in the north/south axis.

Length_EW

m

Maximum length of the 3D region in the east/west axis.

Depth_minimum

m

Minimum depth (below mean sea level) of the 3D object

Depth_maximum

m

Maximum depth of the 3D region.

Height

m

Height of the 3D region (Depth_maximum-Depth_minimum).

Volume

m3

Volume of the 3D region. This does not include the volume of any vacuoles in the 3D region. To include the volume of vacuoles add Total_vacuoles_volume (below).

Geometric_center_latitude

degrees

Latitude of the point at the geometric center of the 3D region.

Geometric_center_longitude

degrees

Longitude of the point at the geometric center of the 3D region.

Geometric_center_depth

m

Geographic depth (below mean sea level) at the geometric center of the 3D region.

OBB_length1

m

Longest dimension of the object-aligned bounding box.

OBB_length2

m

Next longest dimension of the object-aligned bounding box.

OBB_length3

m

Shortest dimension of the object-aligned bounding box.

OBB_axis1_elevation

degrees

The angle between the longest axis of the object-aligned bounding box and the horizontal. Ranges from -90 (vertical downwards) through 0 (horizontal) to 90 (vertical upwards).

OBB_axis1_azimuth

degrees

The angle between the longest axis of the object-aligned bounding box and north. Ranges from 0 (north) through 90 (east) and 180 (south) to 360 (north)

OBB_axis2_rotation

degrees

The angle of rotation of the second longest axis of the object-aligned bounding box about the longest axis when viewed in the upward sense of the longest axis. Ranges from 0 (horizontal) to 90 (most upward direction) to 180 (horizontal).

Intersection_area_first_ping

m2

Intersection area between the 3D region and first ping in the variable used to create it (by detecting schools). This is intended to provide some suggestion as to how much of the detected school may lie outside of the available data (have not been insonified). Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Intersection_area_last_ping

m2

Intersection area between the 3D region and last ping in the variable used to create it (by detecting schools). This is intended to provide some suggestion as to how much of the detected school may lie outside of the available data (have not been insonified). Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Intersection_area_first_beam

m2

Intersection area between the 3D region and first beam in the variable used to create it (by detecting schools). This is intended to provide some suggestion as to how much of the detected school may lie outside of the available data (have not been insonified). Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Intersection_area_last_beam

m2

Intersection area between the 3D region and last beam in the variable used to create it (by detecting schools). This is intended to provide some suggestion as to how much of the detected school may lie outside of the available data (have not been insonified). Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Intersection_area_maximum_range

m2

Intersection area between the 3D region and the furthest sample range in the variable used to create it (by detecting schools). This is intended to provide some suggestion as to how much of the detected school may lie outside of the available data (have not been insonified). Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Roughness

/m

Surface area of the 3D region divided by volume of the 3D region.

Acquisition_start_date

yyyymmdd

The date of the first ping that contained the 3D region. Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Acquisition_start_time

hh:mm:ss

The number of hours, minutes and seconds since midnight of the first ping that contained the 3D region. Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Acquisition_start_ms

ms

Number of milliseconds after the Acquisition start time of the first ping that contained the 3D region. Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Acquisition_stop_date

yyyymmdd

The date of the last ping that contained the 3D region. Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Acquisition_stop_time

hh:mm:ss

The number of hours, minutes and seconds since midnight of the last ping that contained the 3D region. Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Acquisition_stop_ms

ms

Number of milliseconds after the Acquisition stop time of the last ping that contained the 3D region. Note: this does not refer to pings in the variable chosen for analysis, but pings in the variable used for school detection.

Vacuoles

-

Number of vacuoles in the 3D region.

Total_vacuole_volume

m3

The total volume of the vacuoles in the 3D region. Add this to Volume (above) to determine the total volume enclosed by the 3D region.

3D region integration variables

The following integration variables are output when you export a 3D regions analysis but only if an Analysis variable and Integration algorithm are chosen on the Analysis page of the Scene Properties dialog box. See Preparation for exporting integrations from scenes.

Variable

Unit

Description

Sample_mean

same units as the variable chosen for analysis.

The mean value of all the sample values contained within the region. This mean is taken in the linear domain if the variable being analyzed is in dB.

N_sigma_bs

m2

An analysis variable useful for the purposes of biomass estimation.

Volume_integration

m3

An estimate of the physical volume contained within the domain being analyzed.

Sv_mean

dB re 1m-1

Sv mean is the mean Sv within the domain.

Mass_center_latitude

 

The latitude, longitude and depth (below mean sea level) respectively of the calculated center of mass of the domain.

Mass_center_longitude

 

Mass_center_depth

 

Samples

-

Number of "good" data samples within the domain. That is samples which do not have a value of no_data.

No_data_samples

-

The number of samples within the domain which have a value of no_data.

Pings

-

Number of pings in the variable being analyzed which intersect with the domain being analyzed.

Beams

-

Number of beams in the variable being analyzed which intersect with the domain being analyzed. See also About multibeam echograms.

Sv_min

dB re 1m-1

Minimum Sv value within the domain

Sv_max

dB re 1m-1

Maximum Sv value within the domain

Species_ID

-

Species ID number.

Species_name

-

The name of a species as defined on the Species Properties dialog box.

Species_percent

%

Expected proportion of individual members of this species (identified by Species_name) to the whole (all specimens in the domain) - as defined on the Species Properties dialog box)

Species_TS

m2

Expected Target Strength of individual members of the species (as defined on the Species Properties dialog box)

Species_weight

kg

Expected weight of individual members of the species (as defined on the Species Properties dialog box).

Density_number

/m3

The volumetric density of fish expressed in fish numbers.

Density_weight

kg/m3

The volumetric density of fish expressed in mass units.

Fish_number

-

The number of fish of this species (identified by Species_name) in the domain.

Fish_weight

kg

The weight of fish of this species (identified by Species_name) in the domain.

Surface metrics

The following variables are output for each point in a surface when you export a surface to a .csv file.

Variable

Unit

Description

Latitude

Degrees

The latitude of the point.

Longitude

Degrees

The longitude of the point.

Depth

m

The depth (below mean sea level) of the point.

Also on the General page of the (3D Object) Properties dialog box the following analysis variables can be viewed:

Variable

Unit

Description

Vertices

-

Number of vertices in the surface.

Triangles

-

Number of triangles in the surface.

Surface_area

m2

Surface area of the surface.

Length_NS

m

Maximum length of the surface in the north/south axis.

Length_EW

m

Maximum length of the surface in the east/west axis.

Depth_minimum

m

Minimum depth (below mean sea level) of the surface.

Depth_maximum

m

Maximum depth (below mean sea level) of the surface.

Height

m

Height of the surface (Depth_maximum-Depth_minimum).

3D region track metrics

The following variables are output for each point in a 3D region track when you export a region tracks analysis to a .csv file (one line per 3D point in the track).

Variable

Unit

Description

Region_track_group_name

-

Region track_group name.

Region_track_group_id

-

Identification number of the 3D Region track group.

Region_track_name

-

Region track name.

Region_track_id

-

Identification number of the 3D Region track.

Track_point_index

-

Index number of the 3D point in the 3D Region track. The first point is numbered 0.

Track_point_latitude

degree

Latitude of the 3D point.

Track_point_longitude

degree

Longitude of the 3D point.

Track_point_depth

m

Depth (below mean sea level) of the 3D point.

Track_point_velocity_latitude

m/s

Speed in the latitude dimension measured between the current and the previous points in the track.

Track_point_velocity_longitude

m/s

Speed in the longitude dimension measured the current and the previous points in the track.

Track_point_velocity_depth

m/s

Speed in the depth dimension measured the current and the previous points in the track.

See also

About exporting analyses
Exporting integrations

About interval and layer values in export files

About analysis domains

Exporting data

Export file formats

Export variable lists