Ba  k  a  e  -A  aly  e

HN104  —  06/2016

13

calibrated  setup  is  not  posable  in  a  laboratory  en
vironment  due  to  the  aze  of  the  instruments  and
acoustic  range  requirements  Deviations  from  the
laboratory  measurementsare  also  likely  to  occurfol
lowing  the  nal  installation  con  guration  on  board
a  ship  and  due  to  normal  wear  and  tear  of  elec
tronic  and  acoustic  components  For  these  reasons
it  is  imperative  that  a  eld  calibration  procedure  be
performed  to  account  for  the  sector  patternsof  me
dium  and  deep  seamultibeam  echo  sounders
Thecalibration  proceduredeveloped  bylFFEMER
aims  at  more  accurately  modelling  the  sector  pat
terns  of  multi  sector,  multi  swath  multibeams  by
direct  analysis  on  real  time  collected  backscatter
images  To  be  successfully  completed,  the  proce
dure  requiresacalibration  survey  to  be  performed
and  subsequent  analysisof  the  backscatter  images
using  the  IFPEMERsoftware  SbnarStope.  The  cali
bration  survey  areas  must  be  chosen  carefully  in
order  to  optimise  the  quality  of  the  analysis  Rat,

suitably  deep  and  geologically  uniform  seabed
areas  must  be  pre  selected  for  the  calibration  sur
vey.  A  series  of  opposite  running  survey  lines  are
then  run  for  each  Transmission  Mode.
SLich  a  calibration  survey  and  subsequent
backscatter  data  analysis  was  performed  for  the
EM  of  OOGS>Amundsen«.  The  guresdemon
stratethee  ectivenessof  the  procedure.  The  Shal
low,  Dual,  CWTransmission  Mode  isused  asacase
example.
Rg.  a  shows  the  angular  compensated  ESim
age  in  ping  vs  beam  geometry  resulting  from  the
fongsberg  real  time  data  reduction  process  for
the  Shallow,  Dual,  CWTransmission  Mode.  Rg.  b
shows  the  mean  ESangular  curve  obtained  from
the  EBimage  by  averaging  the  ESvaluesin  °  bins
and  colour  coding  curve  segments  by  unique
transmission  sector.
9ep  of  the  calibration  procedure  consists  in
removing  the  ESangular  response  model  used  in

Rg.  3:  Angular  compensated
ESimage  In  ping  vsbeam
geometry  (a,  left)  and
corresponding  angular
response  (b,  right)  for  the
Shallow  Dual  CWTransmission
Mode

Rg.  4:  Transmission  sector
patterns  Image  In  ping  vs
beam  geometry  (a,  left)
and  corresponding  angular
response  (points)  and  models
01  nes)  (b,  right)  for  the  Shallow
Dual  CWTransmission  Mode

Rg.  5:  Calibrated  and  angular
compensated  BSImage  In
ping  vsbeam  geometry
(a  left)  and  corresponding
angular  response  (b,  right)
forthe  Shallow  Dual  ON
Transmission  Mode