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This format is further described in the manufacturer's documentation: 900-00007904-2.1.pdf. (Here's a more recent version: Singlebeam_SMB_V0230.pdf, however, our SMB format is based on the older format specification.) The MATLAB library we use to produce MAT file and plots from SMB files is available upon request. In the replication of the SMB file, the sonarAngle, also known as the startAngle from EXTRA_HIGH_FREQ_SONAR_TUPLE_DATA is corrected to a bearing relative to true North. The correction from instrument relative bearing to true bearing uses the following, in descending order:

  • device true heading from Oceans 2.0 metadata, specified using a fixed heading or a mobile position sensor plus the sitedevice offset. For example: https://data.oceannetworks.ca/DeviceListing?DeviceId=11401 → site tab → https://data.oceannetworks.ca/Sites?siteId=1000659 where offset heading 181 degrees (site fixed heading is not required - only one of site heading or offset heading are, but are additive if both provided).
  • onboard compass, if equipped (new for spring 2021). If the device attribute compass is "ON", the instrument driver software will poll the compass at the start of each SWEEP or SCAN and that data is passed into the SMB file as a DATA_TYPE_HDM tuple, specifying the magnetic heading. A declination correction is applied for the latitude of the device.

This differs from the operation of a rotary sonar onboard a moving vehicle using the MS1000 software: the compass or heading isn't applied to the startAngle, but instead MS1000 rotates the compass rose on the display, keeping the instrument axis pointed up. The compass data appears in the DATA_TYPE_HEAD_SENSORS tuple. In our use case, we're interested in the plot relative to true North, so North is always up. When running an ONC SMB file through MS1000 playback, the software fortunately ignores the compass data, plotting only the sonarAngle/startAngle, which is a true bearing so that the plot on screen is correct.

This data product has been tested mostly with MS 1000 version 4.51, while the new version, 5.2, also tests well. Historic data has been reprocessed and sweep SMB files should be fully available. If a data search returns with 'No data found' when the data availability shows that there is data, please contact us and we will be happy to investigate.

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