BioSonics data files

BioSonics .dt4 format (.dt4)

This file format is used by the BioSonics DT and DE series (4000, 5000 and 6000) echosounders. The file format is described in DT4 Data File Format Specification (version 2.3) and .dt4000/DT5000/DT6000 Transducer EEPROM Format Specification (revision 1.3). Both documents are available from

Echoview supports the reading of a wide range of calibration settings from the BioSonics data files. Some settings are calculated from instrument and environmental values in the data files.

The DT4 file format Position tuple is the source for the position GPS fix variable. The file may contain NMEA data from which Echoview can derive position GPS NMEA string variables and raw line depth variables and heading variables.

BioSonics VisualAquisition 6 software can output Transducer orientation tuple data in DT4 files. Echoview can derive heading, pitch and roll variables from such files. Two BioSonics algorithms are available. One algorithm for vertical-looking data and one algorithm for side-looking data. The algorithm used by Echoview is determined by the BioSonics categorization of the elevation angle of the beam axis. For more information about BioSonics transducer orientation data contact BioSonics.

Echoview reads BioSonics Comment tuples recorded for VisualAquisition Event marker items and creates corresponding marker regions.

BioSonics files can be verified by Echocheck.


  • The Simrad EP500 software can also produce files with a .dt4 extension. These files are not supported by Echoview, however the EY500/EP500 .DG4 file with the same name contains the same data, and is supported by Echoview.
  • DT4 files output by Visual Acquisition 6.0.6 allow selectable sampling rates. With the right sampling rate you can collect BioSonics split beam data up to 1000m in range. Echoview applies a proprietary algorithm to handle such data. For more information contact BioSonics.
  • A line depth data GPGGA variable represents altitude data from the GPS antenna. Positive depths are downward. To convert depth values to altitude, where positive altitude is upward, create a virtual line with the Linear offset operator and set Multiply depth by to -1. Next create an editable line based on the Linear offset operator to use with a Platform or a virtual variable chain. This technique may also be useful for Heave source lines.

The discussion on this page includes the following:

  • Time handling
  • Multiplexed dt4 files
  • File naming
  • Underlying data
  • Calculations
    • Calculation of Sv and TS
    • Differences between Visual Analyzer and Echoview
    • Sv Calculation Warning for Echoview version 2.25 and earlier
    • Calculation of R (the range from the transducer)
    • Calculation of angles for split beam transducers
    • Angle calculation warning
    • Calculation of sound speed and absorption coefficient

Time handling

Time handling in .dt4 data files depends on the ping tuple version number.

Special time handling is required for .dt4 files because ping tuples are not tagged with date and time of day.

V1.0 raw ping tuples

Times for pings between TIME tuples are interpolated. If there are pings before the first TIME tuple, or after the last TIME tuple, then the times for those pings are extrapolated.

V2 ping tuples

The computer system time is included in each tuple. To determine the time for a ping Echoview uses the time from the first TIME tuple in a data file as a time reference and uses the difference between the system time for that tuple and the system time for any other tuple to determine the time of day for the other tuple.

Multiplexed dt4 files

Echoview can read multiplexed DT4 files. If Echoview detects pings before the first TIME tuple then the times for those pings are extrapolated using the next TIME tuple in the file.

File naming

The files must be named in such as way as an alphabetical (text) sorting of the file names will sort them into date/time order.  The BioSonics Visual acquisition software does not necessarily create files in a text sorted order.  Please ensure files are correctly named during logging for correct operation with Echoview.

Underlying data

Underlying data are the above threshold values (in not decoded form) from the BioSonics Sample field. Below threshold data are exported as 65,535. Below threshold data in the BioSonics Sample field have RLE (Run Length Encoded) values.


BioSonics Sv, TS, range and angle calculations are presented as a reference. You do not need to be familiar with this information in order to make use of your data.

Support and feedback

While Echoview has been tested on a significant number of .dt4 files, the interpretation of these files is complex and there may be file format variants which we have not encountered during our testing. If you have a .dt4 file that is not correctly handled by Echoview, please send the file to and we will make the necessary changes to Echoview.

See also

Raw Variables derived from BioSonics data files
Calibration settings for BioSonics data

Support for BioSonics model 102 tuples

BioSonics Sv, TS, range and angle calculations