Ba k a e -A aly e 
HN104 — 06/2016 
11 
Adjustment of backscatter data 
oollected by multi sector multi s/vath 
multibeam echo sounders 
A a lebyJB\n-Qjynl9AD 
Introduction 
Qven the capability of modem swath bathymetry 
multibeam echo soundersto collect co registered 
backscatter data of the seabed, it has become a 
common task for many surveying organisations to 
collect this information in an opportunistic manner. 
While technological innovation and good survey 
practice has rendered bathymetric data collection 
more e dent and measurementsboth precise and 
accurate, so much cannot be said of backscatter 
data Indeed, lack of well establidned measurement 
references and dataprocessng standardshasled to 
a situation where backscatter data may not meet 
predsion and accuracy requirements 
A major detrimental component on backscatter 
measurement is the modulating e ect of the 
echo sounder’s transmission sector pattern(s). In 
post processing, this modulation cannot be dis 
tinguished from the angular dependence of the 
backscatter strength (BE), a best estimate of the 
sea oor acoustic re ectivity, itself an inherent 
property of the sea oor that varies only with the 
incidence angle to the sea oor for a given acous 
tic signal frequency. Traditional statistical angular 
correction methods simply compensate for both 
e ects simultaneously. However, as the BSangu 
lar response should be considered the de facto 
backscatter measurement reference, there is a 
need to separate the respective contributions of 
the BSand the transmission sector pattern®. Only 
through a dedicated eld calibration procedure 
can the latter be accounted for and compensated. 
Wiile the modulating e ect of angle sector 
multibeam echo sounders is not visibly apparent in 
real time backscatter measurements, poorly oom 
pensated or uncompensated transmission sector 
patterns of multi sector multi swath multibeams 
may be visibly apparent. SLich was the case for the 
Canadian ice breaker and research vessel Canadian 
Cbast Guard Snip (C03E) »Amundsen«. Using a eld 
calibration procedure developed by the Institut 
français de recherche pour l’exploitation de la mer 
(IFREMEF), an attempt was undertaken to properly 
While technological innovation and good survey practice has rendered bathymetric 
data collection moree dent and measurementsboth precise and accurate, so much 
cannot be said about backscatter data. Indeed, being more sensitive to geometrical, 
environmental and system-dependent e ects, backscatter measurementssu erfrom 
poor quality when the 
backscatter strength | SbnarStope | multibeam echo sounder latter e ects are not 
accounted for in data 
collection and process 
ing steps A major det 
rimental component on 
backscatter measure 
ments is the modulat 
ing e ect of the echo 
sounder’s transmission 
sector pattern®. This 
e ect is dearly seen 
in backscatter images 
from echo sounders 
with multi-sector and 
multi-swath capabilities 
calibrate the transmission sector patterns of the 
diip’smultibeam echo sounder. Thisartide presents 
the method, analysisand resultsof thisattempt. 
Multi-year surveys in the Canadian 
Arctic Archipelago 
Snce the year , the Canadian ice breaker 
and research vessel 003S »Amundsen« has been 
conducting continuous seabed mapping opera 
tions as part of a multi disciplinary research pro 
gramme. For seabed mapping operations, the ship 
is tted with a Kangsberg Maritime (KM) EM 
kHz multibeam echo sounder (MBEE). The 
EM is a mid ocean depth, multi sector, multi 
swath multibeam echo sounder suitable for the 
depth range of the Canadian Arctic Archipelago 
( to ~ metre$. Rg. presents ’ longitude 
by ’ latitude bathymetry and backscatter maps 
of multibeam data collected on two occasions 
(September nd and th, ) while the ship 
was transiting in the southern Beaufort Sea Wiile 
the digital terrain model (DIM) of Rg. a demon 
strates good consistency, the backscatter mosaic 
ofRg. b does not. 
The backscatter mosaic of Rg. b is the result 
of the Kengsberg real time data reduction proc 
ess, which aims at obtaining a best estimate of the 
angular compensated BSby accounting for all sys 
tern dependent, geometrical and environmental 
components inherent in a complete transmission 
reception cycle. The angular dependence of the 
BS is removed using a simpli ed Lambertian de 
crease model. Qven their geometry and orienta 
tion, changes in BSvalues visible in the backscatter 
mosaic cannot be correlated to changes in the 
composition of the substrate, but rather to inac 
curadesin the Kangsberg real timedatareduction 
process These changes occur both between sur 
vey lines and within individual survey lines Being 
more fundamental, the intra line artefacts need to 
be addressed rst. 
Intra line artefacts taking the form of along 
track bands can easily be traced back to changes 
Author 
Jean Qjy Nistad graduated 
from HCU in Hamburg in 
0 6 with a M.St. degree in 
Gsomaticswith special isation 
in Hydrography. He is currently 
employed by the Federal 
Maritime and Hydrographic 
Agency (BSH) in Fbstock 
jean guy.nistad(§bdi.de 
Nominiert f ür den 
DHyGStudent Excellence 
Award