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Raw variables derived from Navico Group Lowrance (sonar log) data files

Raw variables derived from Navico Group Lowrance (sonar log) data files

This page describes the variables that Echoview can derive from Navico Lowrance data files.

*.slg data
*.sl2 data
*.sl3 data
Using raw variables from Navico Group Lowrance (sonar log) data files

Data processing
Calibration settings
Fileset date and time
Downscan, Sidescan and Sidescan left/right raw variables
Track course raw variables

See also

*.slg data

Derived raw variable may include:

heading data
position GPS fixes
line data sounder detected bottom
unspecified dB single beam pings Primary
unspecified dB single beam pings Secondary

*.sl2 data

Derived raw variable may include:

heading data
track course data (channel n)
position GPS fixes
line data sounder detected bottom
unspecified dB single beam pings Primary
unspecified dB single beam pings Secondary
unspecified dB single beam pings Downscan
unspecified dB single beam pings Sidescan (channel n)
unspecified dB single beam pings Sidescan left (channel n)
unspecified dB single beam pings Sidescan right (channel n)

*.sl3 data

Derived raw variable may include:

heading data
track course data (channel n)
position GPS fixes
line data sounder detected bottom
unspecified dB single beam pings Primary
unspecified dB single beam pings Secondary
unspecified dB single beam pings Downscan
unspecified dB single beam pings Sidescan (channel n)
unspecified dB single beam pings Sidescan left (channel n)
unspecified dB single beam pings Sidescan right (channel n)

n is an integer for the channel ID.

Using raw variables from Navico Group Lowrance (sonar log) data files

Raw variable transducer names may include Echosounder, Image Scan or Transducer. When initally created transducer objects fail to suit your processing needs, use the Dataflow window to associate raw variables with a new custom transducer object.

Many operators in Echoview do not process the unspecified dB format raw variables read from Lowrance data files.

Use the Type conversion operator to convert from unspecified dB to another format. For example, to TS before single target detection or target tracking.

Note: GPS fixes are included and read for every ping. This can result in duplicate fixes that may cause issues for calculations that relate to distance or speed. If this is encountered, export Position GPS fixes to CSV, remove duplicates, then add the cleaned CSV file to a second fileset and use it as the position source for your Platform object.

Note that Bottom classification and vegetation analysis features are not available for Lowrance data.

Read the Downscan and sidescan raw variables section below before undertaking data processing with these raw variables.

Calibration settings

The sample values for the raw variables read from Lowrance data files may exceed the threshold for Echoview's operators.

Use the CalibrationOffsetUnspecifieddB and PulseDuration (e.g., 0.1 ms) calibration settings to adjust the sample values for use with Echoview's operators. When available, PulseDuration is automatically read from Lowrance .sl2 and .sl3 sonar log files via the BurstLength field (pulse duration, in microseconds). Echoview converts BurstLength to milliseconds and uses it to populate the PulseDuration calibration setting for the associated raw variables. Files that report a BurstLength of 0 are treated as not supplying a pulse duration, and PulseDuration can be entered or adjusted manually as needed.

Fileset date and time

*.slg files record a time offset relative to the start time of data recording. The absolute start time is not recorded in the file and must be specified. Do this by using the Fileset Properties dialog box and the options to specify a Start time and/or an Apply time offset. If the Start time is not set, Echoview uses a default date of 1/01/1970 and the time offset read from the file. This information is displayed in the Filesets window and on the Details dialog box.

*.sl2 and *.sl3 files record accurate time stamp information and do not require the user to specify a Start time. The start time recorded in the Fileset window includes the time offset of the first ping.

Downscan, Sidescan and Sidescan left/right raw variables

If available, Echoview reads Downscan and Sidescan raw variables from the data file, and dervies Sidescan left/right raw variables from the latter. However, these are mainly for visualization or experimentation only.

In particular, Sidescan raw variables extend from negative to positive ranges, making them incompatible with many of Echoview's operators. In deriving the Sidescan left and Sidescan right variables, Echoview assumes that the two sides are symmetric and centered at 0 m in range. Echoview inverts the sample range and depth for Sidescan left variables so that they are positive.

Track course raw variables

This is heading data.