About speed data

A speed variable is a time series of the water current speed, and is derived from speed data added to a fileset. The range for speed data is [0, +inf]. The variable can be used with a fixed platform.

What is affected by speed data?

• Grid page Show time/distance grid list.
• Water current speed source on the Position page of the Platform Properties dialog box for a fixed platform.
  • Affects 2D school detection calculations when single beam school Distance mode is set to Water current distance, on the Schools page of the EV File Properties dialog box (Press F6).
  • 2D school detection settings for horizontal lengths are expressed in meters. Also affects the integration schools analysis variables 3D_school_volume and Uncorrected_area.
  • Affects fish tracking analysis variables for horizontal fish track speed, direction and tortuosity.
  • Affects noise removal when backscatter changes with the speed variable.

Calculation of distance from speed data

Where:

dLatest is the latest distance (m)

u is speedLatest the latest speed (ms-1)

t = timeLatest - timePrevious is the difference between the latest and previous times (seconds)

a = (speedLatest - speedPrevious)/(timeLatest - timePrevious) is the acceleration between the latest and previous speeds (ms-2)

dPrevious is the previous (cumulative) distance (m)

Notes:

• When the ping time is before the first speed datum, the first speed datum of the speed variable is used.
• When the ping time is after the last speed datum, the last speed datum of the speed variable is used.

See also

Exporting speed data
Speed graph
Speed data file format
Platform Properties dialog box
2D school detection
Fish tracking