How-to Kongsberg Multibeam - Reference Position

Starting with version 8.16 Qinsy switched to using the Kongsberg reference position as the node location for shallow water multibeam systems.

On this page:

Applicable models

The reference position is used for the following models:

• EM2040P
• EM2040C
• EM3002

In other words combined Tx/Rx transducer arrays.

Explanation

In previous releases, clients would need to enter the actual Tx/Rx phase center locations or a common acoustic center.  These were offset from the geometric center of the sonar head surface.
From now on (from Qinsy 8.16) Qinsy uses Kongsberg's reference positions of the transducers and then computes the actual phase centers of the Transmit and Receive array relative to the reference position (typically the geometric center of the transducers). 
For systems that are configured as having a common acoustic center this means that we are able to perform better footprint calculation. This does mean that the resulting data is different from previous Qinsy releases. 
This change brings Qinsy in line with how Kongsberg SIS and Qimera handle the data.

For the setup of a multibeam it is now necessary to set a model. In the wizard a selection of the model can be made.

Transition of old databases

Warning

If previously you were using EM2040C with separate Tx/Rx nodes you can choose to not update the nodes (use "Other" for model) or you can determine the new reference position.

When template databases are detected with a Kongsberg system then it is detected when the model is not set. A wizard will then start that helps in making the transition.

1. Backup of databases.
   
   A backup is made of each database that is updated. The backup file is located in the same location as the original database file. 
   The backup database will have a *.db_backup file extension.
   

   

   
   
   
2. Select the model
   

   

   
   
   
3. The node changes are shown and can be verified
   
   During any installation pitch, roll and heading angles of the sonar heads will be automatically taken care of.
   

   

   
   
   New nodes have been added to Database Setup and they have been selected in the multibeam system setup, see below.
   

   

With version 8.16 and up the new calculation method will always be used.
This means that the template databases must be modified in order to finally output correct results.

Replay of old recorded databases with a new version

Recorded databases can still be replayed with newer versions and the same results will be generated.

For obtaining new results with the new calculation method the following method needs to be used:

1. Start the update utility from the Program folder
2. The utility will show the recorded databases and Model selection can be done
3. Replay the data

Actual differences

The differences that were found between old and new calculations are really small: The largest differences were found in EM3002 dual head data with differences around 1 or 2 centimeters at a depth of 15 meters.
At other depths and with other systems the differences are negligible. 

Documentation

The Drivers Manual has been updated to indicate that the Kongsberg reference position needs to be used from now on. 

Qinsy supports the following units:

• EM122
• EM302
• EM710
• EM3000
• EM3002
• EM2040
• EM2040C
• EM2040P
• EM2040M
  
  Note that the EM122, EM302 and EM710 systems do not have phase center offsets and are unaffected.
  The EM3000 is also unaffected.

Tip

In case users doubt the offsets then it is recommended to consult the original ship survey documentation to determine the surveyed offsets to the center of the transducers.

Please use these offsets in Qinsy now and make sure that the correct model is set.

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