Sound Metrics data files

DIDSON and ARIS position, pitch, roll and heave variables

Echoview examines position, pitch, roll and heave data recorded with the first ten pings of the file. When data values are missing for all of the first 10 pings, no variable is created.

DIDSON (.ddf)

DDF_03

The DDF_03 version of the DIDSON file format is supported in Echoview.

This file format consists of a master file header followed by one or more frames of data. Both snap shot (master header and a single frame) and movie format files (master header and multiple frames) are supported. Data is displayed in a multibeam echogram where frames correspond to pings.

Each 8-bit underlying data sample stores a number from 0 to 255 representing 0 to 90 dB when processed - these can be exported as underlying data. No phase information is available.

The range (see also note) of each data point is calculated as follows:

Start Range = WindowStart * DelayPeriod * C / 2.0;
Stop Range = Start Range + SamplesPerChannel * C / (2.0 * SampleRate);

Where:

WindowStart is determined from the data file and is 0, 1, 2, or 3
SampleRate is determined from the data file (Hz)
SamplesPerChannel is determined from the data file, typically 512 (integer)
C is the sound speed entered on the Calibration page of the Variable properties dialog box (m/s)
DelayPeriod is determined from the data file using the following lookup table:

   
HighResolution
  SN
No
Yes
  <=18 0.001024 0.000512
  >18 0.001144 0.000572

Where:

HighResolution is determined from the data file (yes or no)
SN is determined from the data file (integer)

The range of any one sample then is calculated as:

Range = C / 2.0 * (WindowStart * DelayPeriod + (n + 0.5) / SampleRate)

Where n = 0 to SamplesPerChannel-1

DDF_04

The DDF_04 version of the DIDSON file format is supported in Echoview. This data format accommodates additional information in the frame headers. The major difference from the DDF_03 format defined above is that the master file header has been expanded from 512 bytes to 1024 bytes, and the frame headers have been expanded from 256 bytes to 1024 bytes.

Range calculations are the same as those for the DDF_03 data file format.

Echoview derives position GPS fixes from the frame header fields m_dlatitude and m_dlongitude. These values represent the data from an installed AUX GPS sensor.

When the first ping contains data in the frame header fields m_fSonarPan, m_fSonarRoll, and m_fSonarTilt; Echoview will derive raw variables for heading, roll, and pitch. Heading data affects the platform. Roll data and pitch data can affect variables.

Notes

ARIS data files (.aris)

Echoview supports *.aris format files output by Sound Metrics ARIS imaging sonars. This file format consists of a master file header followed by one or more frames of data. ARIS parameters and data is stored in the master file header and frame headers. Data are displayed in a multibeam echogram where frames correspond to pings. For more information about ARIS instruments refer to the Sound Metrics website.

The Start range and Stop range are calculated as follows:

Start range = DelayPeriod x SoundSpeed / 2.0

Stop range = Start range + WindowLength

where:

DelayPeriod
=

SampleStartDelay * 0.000001, where SampleStartDelay is read from the Frame header in the data file.

SoundSpeed
= SoundSpeed read from the Frame header in the data file.
WindowLength
=

SamplesPerChannel * SoundSpeed / (2.0 * SampleRate), where SamplesPerChannel is read from the Master header and  SamplePeriod is read from the Frame header and SampleRate = 1 / (SamplePeriod * 0.000001)

See also

Raw variables derived from Sound Metrics data files
Calibration settings for DIDSON data

Calibration setting for ARIS data
Multibeam display note
Sound Metrics notes
Multibeam magnitudes to Sv