Note: Simrad is a subsidiary of Kongsberg. See also Simrad data files.
Echoview supports data files from the following Kongsberg echosounders:
These files contain multibeam data logged from an EM 710 echosounder. Data is represented in Echoview on multibeam echograms.
These files contain a series of datagrams. Only the Water column, Position and Heading datagrams are read. All other datagrams are ignored.
The Kongsberg EM 710 echosounder can have up to 512 beams. In all other respects, the data read from EM 710 (.all) files is treated in the same way as EM 3002 (.all) data files.
These files contain multibeam data logged from an EM 3002 echosounder. Data is represented in Echoview on multibeam echograms.
These files contain a series of datagrams. Only the Water column, Position and Heading datagrams are read. All other datagrams are ignored.
The Water column datagram records a single ping, and is interpreted as follows:
The minimum range of a ping is assumed to be 0 meters.
The maximum range for any beam is calculated as:
Maximum Range = Sample Thickness x (Start Range Sample Number + Maximum Number of Samples) x 0.5
Where:
Sample Thickness = Sound Speed / Sampling Frequency (m)
Sound Speed is read from the Water column datagram (m/s)
Sampling Frequency is read from the Water column datagram (Hz)
Start Range Sample Number is read from the Water column datagram (one value per beam)
Maximum Number of Samples is read from the Water column datagram (one value per beam)
The maximum range of a ping is the largest of the maximum ranges for all beams in that ping.
Note: The EM 3002 format supports different ranges for each beam, Echoview supports a uniform range for all beams only. Beams shorter than the longest beam are padded with no data samples by Echoview.
The raw variable "unspecified dB pings " contains the sample amplitudes calculated as follows:
Amplitude = Stored Value * 0.5 (dB)
Where:
Stored Value is an integer from -128 to 127 as read from the Water column datagram.
Note: Amplitudes may therefore range from -64 to 63.5 dB. The reference is currently unknown.
The raw variable "Sv pings" contains Sv data derived from the amplitudes of the unspecified dB variable as described in Multibeam Magnitudes to Sv. Please note that unspecified dB amplitudes of -64dB are interpreted as below threshold data (-999dB) in the derived Sv variable.
The value of TVG embedded in the recorded data is specified by the TVG function applied field in the Water Column datagram.
Individual beams may have different beam widths and ranges. Echoview supports varying beam widths in multibeam data, but currently supports only a constant range for all beams. As a consequence, echograms of EM 3002 data are filled to the maximum range with no data. That is, in Echoview all beams are of equal range and samples which are not available in the Water column datagram are given the value "no data". These samples are typically displayed in the background color, but they are there and will appear in exports and influence the display of echograms.
The beam angles read from .all files are negated (multiplied by -1) in Echoview to ensure that the EM 3002 multibeam echogram display conforms with Echoview norms: Beam 1 being on the far left with a negative beam angle.
Echoview supports two distinct versions of the .all file format. A significant change to the format was introduced on December 17th 2004. Echoview distinguishes between them on the basis of the TVG function applied field in the Water Column datagram. Old format files have 0 for this value (this space in the datagram was occupied by two spare bytes in the old format), and new format files contain a number from 20 to 40. The obtained TVG fuction applied value is used in the calculation of Sv, meaning that old format files will use a TVG correction of 0.
Note: Echocheck will report which format (new or old) is detected.
These files contain multibeam data logged from an EM 3002 echosounder with a dual head (D). Data is represented in Echoview on multibeam echograms. Separate variables are derived from data associated with the second head. In all other respects data is treated as for EM 3002 data files.
The MS 1000 scanning sonar uses a single beam which scans by varying the tilt and bearing of the beam. The resulting data is represented in Echoview by one H-mode ping with no data samples on all beams except the single beam recorded.
You can use the beam scan operator to generate H-mode pings with more than one beam containing data.
Echoview supports 8-bit or 4-bit (compressed) sample data in MS 1000 data files. The 4-bit data is uncompressed using an algorithm provided by Kongsberg.
Note: Prior to Echoview 4.60, 4-bit sample data was not supported. 4-bit sample data was incorrectly read by Echoview and problems with such files only appeared when you scrolled to the end of the echogram.
Echoview reads from the EXTRA_HIGH_FREQ_SONAR_TUPLE_DATA header the values of StepSize and StartAngle.
StepSize is used to calculate the number of H-mode beams used to represent the ping:
Number of beams = 360 / (StepSize x 0.225)
where StepSize is in 0.225ths of a degree.
StartAngle is used to calculate the number of the beam in this H-mode ping which is populated with data:
Beam number = StartAngle x 0.225 x Number of Beams / 360
where StartAngle is in 0.225ths of a degree and beam number 0 is taken to be in the direction of travel (for a moving platform) or north (for a fixed platform).
Echoview reads from the DATA_TYPE_SETTINGS tuple the value of TiltSectorHeading, which is used to calculate the tile angle as follows:
Tilt angle = TiltSectorHeading x 0.225
Where TiltSectorHeading is in 0.225ths of a degree.
Echoview reads from the EXTRA_HIGH_FREQ_SONAR_TUPLE_DATA header the values of SamplingRate and SamplingDelay and from the DATA_TYPE_SETTINGS tuple the value of SampCount.
SamplingRate is used to calculate the sample thickness as follows:
Sample thickness = Sound speed / SamplingRate / 2
where Sound speed is taken to be 1500 m/s and SamplingRate is in Hertz.
SamplingDelay is used to calculate the start range as follows:
Start range = SamplingDelay * Sample thickness
SampCount is used to calculate the stop range as follows:
Stop range = Start Range + SampCount x Sample thickness
The magnitudes are read for the DATA_TYPE_SONAR tuple and stored as single number from 0 to 255 representing the received signal strength with a time varied gain applied.
The received power is calculated for Sv calculations as follows:
Pr = 20log(Magnitude)
where Magnitude is the number form 0 to 255 read from the data file Pr is in dB and used in the Sv equation.
Echoview reads from the DATA_TYPE_SETTINGS tuple the value of TvgAFactor for use in calculating Sv. It is typically 20, 30 or 40.
The Kongsberg SM20 system consists of a Simrad SM2000 multibeam echosounder and an SM20 specific processing PC and software. In Echoview, there may be some small differences between SM20 and SM2000 data files:
Beamformed and unbeamformed data are represented in Echoview as multibeam echograms.
Raw variables derived from Kongsberg data files
Calibration settings for EM 3002 data
Calibration settings for EM 3002D data
Calibration settings for MS 1000 data
Calibration settings for SM20 data