Triton Isis and Triton SS-Logger now support (from v7.1) the logging and replay of XTF data with the Edgetech weighting factor. Storing and using weighting in the XTFPINGCHANHEADER allows the data to be processed through floating point expansion, in this case the displayed sample value is equal to <16bit sample value>*Pow(2,-Weight) This allows for floating point granularity in the data while storing the data as 16 bit integers.
Edgetech "Discover" version note: Make sure you are running Discover version 5.30 or higher.
From the users point if view the implementation of the weighting factor means that there is now no need to manually set a fixed gain in the 4200 (or MPX) servers. The bar graphs associated with that setting have disappeared from the 4200 server.
There is now a second Normalize slider that is accessed from the Waterfall Display dialog (right click in the Isis waterfall window). The control will only be available when Isis detects that the sonar type supports weighting. XTF files recorded with other sonar types are unaffected. The normal setting will be Auto, however the user also has the ability to force the weighting to be On or Off:
At the time of writing the Normalizer setting defaults to zero which usually results in a completely black record, the settings will need be determined by the user, however most data seen so far require the slider to be set around 13 or 14.
In later versions of Isis the values for threshold and weighting will default to 1 (threshold) and 9 (weighting)
Isis cannot determine if the data actually contain the weighting factor. It will always assume that data from Edgetech sonars that support weighting will have weighting, so the slider will be enabled. However, in a file from an Edgetech sonar that supports weighting but does not have weighted data the weighting read from the XTF file will be a constant value of zero. The Normalization slider will simply change the perceived gain of the display in a similar way to the Threshold slider.
Playing back a file that has weighting and forcing the weight to OFF will result in bands of strong and weak data where the 16bit weighted signal value is changing but the appropriate weighting value is not being applied (see below)
Fig 1 File with weighting played back with weighting OFF (wrong)
Fig 2 The same file with weighting ON (correct)
In record mode the user has no control over the raw data written to the XTF file, if the sonar supports weighting the data will be logged with weighting values. If an incorrect Normalize setting should used during logging this has no affect on the data logged to the XTF file, since it is simply a waterfall display function.
NOTE: using earlier versions of Isis or SS-Logger to play back Edgetech data stored with a weighting value will result in a display similar to Figure 1.