Kongsberg Maritime offers a new solution to improve the quality of Multibeam Backscatter data. The service uses KONGSBERG Multibeam models to produce compensated backscatter data,
with data samples adjusted for mode dependent system parameters, such as:
- Transmitter Source Level
- Receiver sensitivity
- Transmitter and receiver beam pattern
- Receiver gain
- Transmit pulse length and bandwidth
- Spherical spreading and frequency dependent absorption
- Insonified area on bottom
- Incidence angle
- Vessel attitude
The measured backscatter level is also influenced by the actual transducer installation on the vessel. Other factors that can change the backscatter level include e.g., marine growth. To ensure optimum
backscatter level, a calibration at sea should be performed.
The new Backscatter Calibration Service produces calibration table files based on survey lines recorded by the multibeam echo sounders. The service is available for EM 122, EM 302, EM 710 and EM 712
and EM 2040 series multibeams.
The service uses a software package that can reprocess surveyed data by correcting the backscatter levels and making new *.all files. The software package will be compiled by Kongsberg Maritime Customer
Services for the actual echo sounder and will contain the calibration file. The calibration file can be installed on the echo sounder and used in real time*.
The procedure is as follows
- The customer logs the survey lines needed. A procedure for this is available
- The survey lines are transferred to Kongsberg Maritime Customer Services
- Customer Services analyses the data and makes a calibration file
- The calibration file is sent to the customer and installed on the echo sounder
- The calibration file is then used in real time to adjust the backscatter data. The calibration file is logged together with the data (in the *.all file)
Normally the bottom backscatter level (BS) at the test area is unknown. The average BS level of the logged lines is then used as the reference level BSref.
If the test area BS is known, this value can be defined as BSref. By using a common test area for several multibeams, a common reference can then be used, assuring comparable results.
* The EM 2040 series does not currently support use of calibration files in real time. When the new datagram format becomes available, use of calibration data in real time will
be in place also for the EM 2040 series.