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Ba k a e -A aly e HN104 — 06/2016 15 The modelling proved quite di cult given the poor quality of the real time backscatter measure merits A much more successful approach, and one which is currently being investigated at IFRE MER is to use a BS model obtained from another calibrated echo sounder (single beam or split beam) mechanically steered at several transmis sion angles in order to obtain a more realistic BS angular response curve. Nevertheless, the calibra tion survey and subsequent analysis allowed for a substantial improvement in the precision of the mean BSvalue of the BSmosaics Cbmpared to other multibeam echo sounders previously investigated by the author, the EM installed on OOGS»Amundsen« shows very strong transmission sector patterns modulations Several attempts were made to nd the causes of these modulations During this investigation, it was dis covered that some of the transmit channelsof the EM are in adegraded state. However, the most plausible explanation is the fact that the EM ’s transducers are encased behind a titanium en forced polymer protective window which is likely to a ect the transmitted source level and sector patternssigni cantly more than for normal vessels For operations in ice, this window is however es sential to the protection of the transducers Cbnclusion This project has focused on the application of a unique calibration procedure dedicated to the compensation of transmission sector patterns of multi sector, multi swath multibeam echo sound ers Uncalibrated transmission sector patterns modulate the backscatter reqconse and are visible as intra line artefacts The calibration procedure was applied on backscatter data collected by 003S »Amundsen«. The procedure included the success ful conduct of a calibration survey in the Canadian Arctic and subsequent analysis of the backscatter data usng the software SbnarSCope. The precision of the mean BSvalue of virtually all Transmission Modesisimproved in the to degreesangular range. Ftesidual sector boundary steps remained problematic and visible in the calibrated images, and overall, the calibration could be improved with better estimation of the parameters of the BS model. Indeed, due to the multibeam echo sounder’s protective window deteriorating the raw backscatter measurements, the modelling of the BSfrom empirical data proved di cult. Several investigations were carried out in order to identify the cause of a remaining inter sector bias This lead to the discovery of tranamisaon channel problems However, the cause of the bias was most likely due to ahardware software incompatibility. The fact that this problem did not lead to any discernible artefact on the bathymetry data highlights the fact that backscatter measurementsare more senativeto changesin system dependent parameters Multibeam backscatter o ersseveral applications in seabed dassi cation, habitat mapping and sea bed monitoring. These applications can potentially be very bene dal in fundamental sciencessuch as geology and benthic biology and ecology. Sden tists wishing to mate use of multibeam backscatter must however be fully aware of the limitations and pit fallsof multibeam echo sounder measurements Most notably, the status of the instruments should be well understood, the context under which the datawascollected and the processing applied prior to delivery should be well controlled." Fig. 7: Angular compensated BSmosaic following the transmission sector pattern calibration (a left) and following a statistical compensation to remove the remaining OdBInter line bias (b, right) Acknowledgements The author would like to add ress thanks to the following Individuals: Jean Marie Augustin (IFFBVIB^ for hlsguldance and for providing a loan of SonarSbope for t h Is p roj ect ; Rof. Harald Sernberg (HCU) for his supervision; Rof. Rrtrlck Lajeunesse (Université Laval) for providing the opportunity to participate on an expedition onboard (DOGS »Amundsen«; Gabriel Jeyal (Université Laval) for assisting In the data col lection.